extraclangtools - Man Page

This document contains the release notes for the Extra Clang Tools, part of the Clang release 19.1.4. Here we describe the status of the Extra Clang Tools in some detail, including major improvements from the previous release and new feature work. All LLVM releases may be downloaded from the LLVM releases web site.

For more information about Clang or LLVM, including information about the latest release, please see the Clang Web Site or the LLVM Web Site.

Note that if you are reading this file from a Git checkout or the main Clang web page, this document applies to the next release, not the current one. To see the release notes for a specific release, please see the releases page.

Some of the major new features and improvements to Extra Clang Tools are listed here. Generic improvements to Extra Clang Tools as a whole or to its underlying infrastructure are described first, followed by tool-specific sections.

...

• Introduced exmperimental support for C++20 Modules. The experimental support can be enabled by -experimental-modules-support option. It is in an early development stage and may not perform efficiently in real-world scenarios.

• Improved semantic token coverage in some edge cases, e.g. IndirectFieldDecl

• --function-arg-placeholders=0 is now respected for variable template argument lists

  as well

• Macro proposals now use the completion item kind Constant (for object-like macros) or Function (for function-style macros) even for proposals coming from the index

• The "extract variable" tweak is no longer offered for the initializer expression of a declaration
• The tweak for turning unscoped into scoped enums now removes redundant prefixes from the enum values.
• Support "move function body out-of-line" in non-header files as well

• Signature help now shows function argument names for calls through pointers to functions in struct fields

• Improve go-to-definition for some concept references

• Improved precision of document outline information for symbols whose definitions involve macro expansions

• The quick fix for clang-tidy's readability-identifier-naming diagnostic is now hooked to invoke textDocument/rename, renaming the identifier across the whole project rather than just the translation unit of the diagnostic
• misc-const-correctness can now be enabled with FastCheckFilter: None (previously clangd would force it off unconditionally due to its run time)

• Added support for renaming Objective-C methods

• Worked around a clang-format bug that caused memory exhaustion when opening some large .h files due to the formatter's language guessing heuristic (#GH85703)
• Various other stability improvements, e.g. crash fixes
• Added a boolean option AnalyzeAngledIncludes to Includes config section, which allows to enable unused includes detection for all angled ("system") headers. At this moment umbrella headers are not supported, so enabling this option may result in false-positives.

• Added the file command to dynamically load a list of commands and matchers from an external file, allowing the cost of reading the compilation database and building the AST to be imposed just once for faster prototyping.
• Removed support for enable output srcloc. Fixes #GH82591

The improvements are...

• Improved run-clang-tidy.py script. Added argument -source-filter to filter source files from the compilation database, via a RegEx. In a similar fashion to what -header-filter does for header files. Added progress indicator with a number of processed files and the runtime of each invocation after completion.
• Improved check_clang_tidy.py script. Added argument -export-fixes to aid in clang-tidy and test development.
• Fixed bug where big values for unsigned check options overflowed into negative values when being printed with --dump-config.
• Fixed --verify-config option not properly parsing checks when using the literal operator in the .clang-tidy config.
• Added argument --exclude-header-filter and config option ExcludeHeaderFilterRegex to exclude headers from analysis via a RegEx.
• Added argument --allow-no-checks to suppress "no checks enabled" error when disabling all of the checks by --checks='-*'.

• New boost-use-ranges check.

  Detects calls to standard library iterator algorithms that could be replaced with a Boost ranges version instead.

• New bugprone-crtp-constructor-accessibility check.

  Detects error-prone Curiously Recurring Template Pattern usage, when the CRTP can be constructed outside itself and the derived class.

• New bugprone-pointer-arithmetic-on-polymorphic-object check.

  Finds pointer arithmetic performed on classes that contain a virtual function.

• New bugprone-return-const-ref-from-parameter check.

  Detects return statements that return a constant reference parameter as constant reference. This may cause use-after-free errors if the caller uses xvalues as arguments.

• New bugprone-suspicious-stringview-data-usage check.

  Identifies suspicious usages of std::string_view::data() that could lead to reading out-of-bounds data due to inadequate or incorrect string null termination.

• New misc-use-internal-linkage check.

  Detects variables and functions that can be marked as static or moved into an anonymous namespace to enforce internal linkage.

• New modernize-min-max-use-initializer-list check.

  Replaces nested std::min and std::max calls with an initializer list where applicable.

• New modernize-use-designated-initializers check.

  Finds initializer lists for aggregate types that could be written as designated initializers instead.

• New modernize-use-ranges check.

  Detects calls to standard library iterator algorithms that could be replaced with a ranges version instead.

• New modernize-use-std-format check.

  Converts calls to absl::StrFormat, or other functions via configuration options, to C++20's std::format, or another function via a configuration option, modifying the format string appropriately and removing now-unnecessary calls to std::string::c_str() and std::string::data().

• New readability-enum-initial-value check.

  Enforces consistent style for enumerators' initialization, covering three styles: none, first only, or all initialized explicitly.

• New readability-math-missing-parentheses check.

  Check for missing parentheses in mathematical expressions that involve operators of different priorities.

• New readability-use-std-min-max check.

  Replaces certain conditional statements with equivalent calls to std::min or std::max.

• New alias cert-ctr56-cpp to bugprone-pointer-arithmetic-on-polymorphic-object was added.
• New alias cert-int09-c to readability-enum-initial-value was added.

• Improved bugprone-assert-side-effect check by detecting side effect from calling a method with non-const reference parameters.
• Improved bugprone-assignment-in-if-condition check by ignoring assignments in the C++20 requires clause.
• Improved bugprone-casting-through-void check by ignoring casts where source is already a void` pointer, making middle void pointer casts bug-free.
• Improved bugprone-exception-escape  check to correctly detect exception handler of type CV void * as catching all  CV compatible pointer types.
• Improved bugprone-forwarding-reference-overload check to ignore deleted constructors which won't hide other overloads.
• Improved bugprone-implicit-widening-of-multiplication-result check by adding an option to ignore constant expressions of signed integer types that fit in the source expression type.
• Improved bugprone-inc-dec-in-conditions check to ignore code within unevaluated contexts, such as decltype.
• Improved bugprone-lambda-function-name check by ignoring __func__ macro in lambda captures, initializers of default parameters and nested function declarations.
• Improved bugprone-multi-level-implicit-pointer-conversion check by ignoring implicit pointer conversions that are part of a cast expression.
• Improved bugprone-non-zero-enum-to-bool-conversion check by eliminating false positives resulting from direct usage of bitwise operators within parentheses.
• Improved bugprone-optional-value-conversion check by eliminating false positives resulting from use of optionals in unevaluated context.
• Improved bugprone-sizeof-expression check by clarifying the diagnostics, eliminating some false positives and adding a new (off-by-default) option WarnOnSizeOfPointer that reports all sizeof(pointer) expressions (except for a few that are idiomatic).
• Improved bugprone-suspicious-include check by replacing the local options HeaderFileExtensions and ImplementationFileExtensions by the global options of the same name.
• Improved bugprone-too-small-loop-variable check by incorporating better support for const loop boundaries.
• Improved bugprone-unused-local-non-trivial-variable check by ignoring local variable with [maybe_unused] attribute.
• Improved bugprone-unused-return-value check by updating the parameter CheckedFunctions to support regexp, avoiding false positive for function with the same prefix as the default argument, e.g. std::unique_ptr and std::unique, avoiding false positive for assignment operator overloading.
• Improved bugprone-use-after-move check to also handle calls to std::forward. Fixed sequencing of designated initializers. Fixed sequencing of callees: In C++17 and later, the callee of a function is guaranteed to be sequenced before the arguments, so don't warn if the use happens in the callee and the move happens in one of the arguments.
• Improved cppcoreguidelines-avoid-non-const-global-variables check with a new option AllowInternalLinkage to disable the warning for variables with internal linkage.
• Improved cppcoreguidelines-macro-usage check by ignoring macro with hash preprocessing token.
• Improved cppcoreguidelines-missing-std-forward check by no longer giving false positives for deleted functions, by fixing false negatives when only a few parameters are forwarded and by ignoring parameters without a name (unused arguments).
• Improved cppcoreguidelines-owning-memory check to properly handle return type in lambdas and in nested functions.
• Improved cppcoreguidelines-prefer-member-initializer check by removing enforcement of rule C.48, which was deprecated since clang-tidy 17. This rule is now covered by cppcoreguidelines-use-default-member-init. Fixed incorrect hints when using list-initialization.
• Improved cppcoreguidelines-special-member-functions check with a new option AllowImplicitlyDeletedCopyOrMove, which removes the requirement for explicit copy or move special member functions when they are already implicitly deleted.
• Improved google-build-namespaces check by replacing the local option HeaderFileExtensions by the global option of the same name.
• Improved google-explicit-constructor check to better handle C++20 explicit(bool).
• Improved google-global-names-in-headers check by replacing the local option HeaderFileExtensions by the global option of the same name.
• Improved google-runtime-int check performance through optimizations.
• Improved hicpp-signed-bitwise check by ignoring false positives involving positive integer literals behind implicit casts when IgnorePositiveIntegerLiterals is enabled.
• Improved hicpp-ignored-remove-result check by ignoring other functions with same prefixes as the target specific functions.
• Improved linuxkernel-must-check-errs check documentation to consistently use the check's proper name.
• Improved llvm-header-guard check by replacing the local option HeaderFileExtensions by the global option of the same name.
• Improved misc-const-correctness check by avoiding infinite recursion for recursive functions with forwarding reference parameters and reference variables which refer to themselves. Also adapted the check to work with function-try-blocks.
• Improved misc-definitions-in-headers check by replacing the local option HeaderFileExtensions by the global option of the same name. Additionally, the option UseHeaderFileExtensions is removed, so that the check uses the HeaderFileExtensions option unconditionally.
• Improved misc-header-include-cycle check by avoiding crash for self include cycles.
• Improved misc-unused-using-decls check by replacing the local option HeaderFileExtensions by the global option of the same name.
• Improved misc-use-anonymous-namespace check by replacing the local option HeaderFileExtensions by the global option of the same name.
• Improved modernize-avoid-c-arrays check by introducing the new AllowStringArrays option, enabling the exclusion of array types with deduced length initialized from string literals.
• Improved modernize-loop-convert check by ensuring that fix-its don't remove parentheses used in sizeof calls when they have array index accesses as arguments.
• Improved modernize-use-constraints check by fixing a crash that occurred in some scenarios and excluding system headers from analysis.
• Improved modernize-use-nullptr check to include support for C23, which also has introduced the nullptr keyword.
• Improved modernize-use-override check to also remove any trailing whitespace when deleting the virtual keyword.
• Improved modernize-use-starts-ends-with check to also handle calls to compare method.
• Improved modernize-use-std-print check to not crash if the format string parameter of the function to be replaced is not of the expected type.
• Improved modernize-use-using check by adding support for detection of typedefs declared on function level.
• Improved performance-inefficient-vector-operation fixing false negatives caused by different variable definition type and variable initial value type in loop initialization expression.
• Improved performance-move-const-arg check by ignoring std::move() calls when their target is used as an rvalue.
• Improved performance-unnecessary-copy-initialization check by detecting more cases of constant access. In particular, pointers can be analyzed, so the check now handles the common patterns const auto e = (*vector_ptr)[i] and const auto e = vector_ptr->at(i);. Calls to mutable function where there exists a const overload are also handled. Fix crash in the case of a non-member operator call.
• Improved performance-unnecessary-value-param check detecting more cases for template functions including lambdas with auto. E.g., std::sort(a.begin(), a.end(), [](auto x, auto y) { return a > b; }); will be detected for expensive to copy types. Fixed false positives for dependent call expressions.
• Improved readability-avoid-return-with-void-value check by adding fix-its.
• Improved readability-const-return-type check to eliminate false positives when returning types with const not at the top level.
• Improved readability-container-size-empty check to prevent false positives when utilizing size or length methods that accept parameter. Fixed crash when facing template user defined literals.
• Improved readability-duplicate-include check by excluding include directives that form the filename using macro.
• Improved readability-else-after-return check to ignore if consteval statements, for which the else branch must not be removed.
• Improved readability-identifier-naming check in GetConfigPerFile mode by resolving symbolic links to header files. Fixed handling of Hungarian Prefix when configured to LowerCase. Added support for renaming designated initializers. Added support for renaming macro arguments. Fixed renaming conflicts arising from out-of-line member function template definitions.
• Improved readability-implicit-bool-conversion check to provide valid fix suggestions for static_cast without a preceding space and fixed problem with duplicate parentheses in double implicit casts. Corrected the fix suggestions for C23 and later by using C-style casts instead of static_cast. Fixed false positives in C++20 spaceship operator by ignoring casts in implicit and defaulted functions.
• Improved readability-non-const-parameter check to not crash when redeclaration have fewer parameters than expected.
• Improved readability-redundant-inline-specifier check to properly emit warnings for static data member with an in-class initializer.
• Improved readability-redundant-member-init check to avoid false-positives when type of the member does not match the type of the initializer.
• Improved readability-static-accessed-through-instance check to support calls to overloaded operators as base expression and provide fixes to expressions with side-effects.
• Improved readability-simplify-boolean-expr check to avoid to emit warning for macro when IgnoreMacro option is enabled and improve messages when auto-fix does not work.
• Improved readability-static-definition-in-anonymous-namespace check by resolving fix-it overlaps in template code by disregarding implicit instances.
• Improved readability-string-compare check to also detect usages of std::string_view::compare. Added a StringLikeClasses option to detect usages of compare method in custom string-like classes.

• Removed cert-dcl21-cpp, which was deprecated since clang-tidy 17, since the rule DCL21-CPP has been removed from the CERT guidelines.

• Fixed incorrect formatting in clang-apply-replacements when no --format option is specified. Now clang-apply-replacements applies formatting only with the option.

The improvements are...

The improvements are...

The improvements are...

• Clang-Tidy

  • Using clang-tidy
  • Suppressing Undesired Diagnostics

See also:

Suggests switching the initialization pattern of absl::Cleanup instances from the factory function to class template argument deduction (CTAD), in C++17 and higher.

auto c1 = absl::MakeCleanup([] {});

const auto c2 = absl::MakeCleanup(std::function<void()>([] {}));

becomes

absl::Cleanup c1 = [] {};

const absl::Cleanup c2 = std::function<void()>([] {});

Check for cases where addition should be performed in the absl::Time domain. When adding two values, and one is known to be an absl::Time, we can infer that the other should be interpreted as an absl::Duration of a similar scale, and make that inference explicit.

Examples:

// Original - Addition in the integer domain
int x;
absl::Time t;
int result = absl::ToUnixSeconds(t) + x;

// Suggestion - Addition in the absl::Time domain
int result = absl::ToUnixSeconds(t + absl::Seconds(x));

Checks for comparisons which should be in the absl::Duration domain instead of the floating point or integer domains.

N.B.: In cases where a Duration was being converted to an integer and then compared against a floating-point value, truncation during the Duration conversion might yield a different result. In practice this is very rare, and still indicates a bug which should be fixed.

Examples:

// Original - Comparison in the floating point domain
double x;
absl::Duration d;
if (x < absl::ToDoubleSeconds(d)) ...

// Suggested - Compare in the absl::Duration domain instead
if (absl::Seconds(x) < d) ...


// Original - Comparison in the integer domain
int x;
absl::Duration d;
if (x < absl::ToInt64Microseconds(d)) ...

// Suggested - Compare in the absl::Duration domain instead
if (absl::Microseconds(x) < d) ...

Checks for casts of absl::Duration conversion functions, and recommends the right conversion function instead.

Examples:

// Original - Cast from a double to an integer
absl::Duration d;
int i = static_cast<int>(absl::ToDoubleSeconds(d));

// Suggested - Use the integer conversion function directly.
int i = absl::ToInt64Seconds(d);


// Original - Cast from a double to an integer
absl::Duration d;
double x = static_cast<double>(absl::ToInt64Seconds(d));

// Suggested - Use the integer conversion function directly.
double x = absl::ToDoubleSeconds(d);

Note: In the second example, the suggested fix could yield a different result, as the conversion to integer could truncate. In practice, this is very rare, and you should use absl::Trunc to perform this operation explicitly instead.

absl::Duration arithmetic works like it does with integers. That means that division of two absl::Duration objects returns an int64 with any fractional component truncated toward 0. See this link for more information on arithmetic with absl::Duration.

For example:

absl::Duration d = absl::Seconds(3.5);
int64 sec1 = d / absl::Seconds(1);     // Truncates toward 0.
int64 sec2 = absl::ToInt64Seconds(d);  // Equivalent to division.
assert(sec1 == 3 && sec2 == 3);

double dsec = d / absl::Seconds(1);  // WRONG: Still truncates toward 0.
assert(dsec == 3.0);

If you want floating-point division, you should use either the absl::FDivDuration() function, or one of the unit conversion functions such as absl::ToDoubleSeconds(). For example:

absl::Duration d = absl::Seconds(3.5);
double dsec1 = absl::FDivDuration(d, absl::Seconds(1));  // GOOD: No truncation.
double dsec2 = absl::ToDoubleSeconds(d);                 // GOOD: No truncation.
assert(dsec1 == 3.5 && dsec2 == 3.5);

This check looks for uses of absl::Duration division that is done in a floating-point context, and recommends the use of a function that returns a floating-point value.

Checks for cases where the floating-point overloads of various absl::Duration factory functions are called when the more-efficient integer versions could be used instead.

This check will not suggest fixes for literals which contain fractional floating point values or non-literals. It will suggest removing superfluous casts.

Examples:

// Original - Providing a floating-point literal.
absl::Duration d = absl::Seconds(10.0);

// Suggested - Use an integer instead.
absl::Duration d = absl::Seconds(10);


// Original - Explicitly casting to a floating-point type.
absl::Duration d = absl::Seconds(static_cast<double>(10));

// Suggested - Remove the explicit cast
absl::Duration d = absl::Seconds(10);

Checks for cases where arguments to absl::Duration factory functions are scaled internally and could be changed to a different factory function. This check also looks for arguments with a zero value and suggests using absl::ZeroDuration() instead.

Examples:

// Original - Internal multiplication.
int x;
absl::Duration d = absl::Seconds(60 * x);

// Suggested - Use absl::Minutes instead.
absl::Duration d = absl::Minutes(x);


// Original - Internal division.
int y;
absl::Duration d = absl::Milliseconds(y / 1000.);

// Suggested - Use absl:::Seconds instead.
absl::Duration d = absl::Seconds(y);


// Original - Zero-value argument.
absl::Duration d = absl::Hours(0);

// Suggested = Use absl::ZeroDuration instead
absl::Duration d = absl::ZeroDuration();

Checks for cases where subtraction should be performed in the absl::Duration domain. When subtracting two values, and the first one is known to be a conversion from absl::Duration, we can infer that the second should also be interpreted as an absl::Duration, and make that inference explicit.

Examples:

// Original - Subtraction in the double domain
double x;
absl::Duration d;
double result = absl::ToDoubleSeconds(d) - x;

// Suggestion - Subtraction in the absl::Duration domain instead
double result = absl::ToDoubleSeconds(d - absl::Seconds(x));

// Original - Subtraction of two Durations in the double domain
absl::Duration d1, d2;
double result = absl::ToDoubleSeconds(d1) - absl::ToDoubleSeconds(d2);

// Suggestion - Subtraction in the absl::Duration domain instead
double result = absl::ToDoubleSeconds(d1 - d2);

Note: As with other clang-tidy checks, it is possible that multiple fixes may overlap (as in the case of nested expressions), so not all occurrences can be transformed in one run. In particular, this may occur for nested subtraction expressions. Running clang-tidy multiple times will find and fix these overlaps.

Finds and fixes cases where absl::Duration values are being converted to numeric types and back again.

Floating-point examples:

// Original - Conversion to double and back again
absl::Duration d1;
absl::Duration d2 = absl::Seconds(absl::ToDoubleSeconds(d1));

// Suggestion - Remove unnecessary conversions
absl::Duration d2 = d1;

// Original - Division to convert to double and back again
absl::Duration d2 = absl::Seconds(absl::FDivDuration(d1, absl::Seconds(1)));

// Suggestion - Remove division and conversion
absl::Duration d2 = d1;

Integer examples:

// Original - Conversion to integer and back again
absl::Duration d1;
absl::Duration d2 = absl::Hours(absl::ToInt64Hours(d1));

// Suggestion - Remove unnecessary conversions
absl::Duration d2 = d1;

// Original - Integer division followed by conversion
absl::Duration d2 = absl::Seconds(d1 / absl::Seconds(1));

// Suggestion - Remove division and conversion
absl::Duration d2 = d1;

Unwrapping scalar operations:

// Original - Multiplication by a scalar
absl::Duration d1;
absl::Duration d2 = absl::Seconds(absl::ToInt64Seconds(d1) * 2);

// Suggestion - Remove unnecessary conversion
absl::Duration d2 = d1 * 2;

Note: Converting to an integer and back to an absl::Duration might be a truncating operation if the value is not aligned to the scale of conversion. In the rare case where this is the intended result, callers should use absl::Trunc to truncate explicitly.

Finds instances of absl::StrSplit() or absl::MaxSplits() where the delimiter is a single character string literal and replaces with a character. The check will offer a suggestion to change the string literal into a character. It will also catch code using absl::ByAnyChar() for just a single character and will transform that into a single character as well.

These changes will give the same result, but using characters rather than single character string literals is more efficient and readable.

Examples:

// Original - the argument is a string literal.
for (auto piece : absl::StrSplit(str, "B")) {

// Suggested - the argument is a character, which causes the more efficient
// overload of absl::StrSplit() to be used.
for (auto piece : absl::StrSplit(str, 'B')) {


// Original - the argument is a string literal inside absl::ByAnyChar call.
for (auto piece : absl::StrSplit(str, absl::ByAnyChar("B"))) {

// Suggested - the argument is a character, which causes the more efficient
// overload of absl::StrSplit() to be used and we do not need absl::ByAnyChar
// anymore.
for (auto piece : absl::StrSplit(str, 'B')) {


// Original - the argument is a string literal inside absl::MaxSplits call.
for (auto piece : absl::StrSplit(str, absl::MaxSplits("B", 1))) {

// Suggested - the argument is a character, which causes the more efficient
// overload of absl::StrSplit() to be used.
for (auto piece : absl::StrSplit(str, absl::MaxSplits('B', 1))) {

Warns if code using Abseil depends on internal details. If something is in a namespace that includes the word "internal", code is not allowed to depend upon it because it's an implementation detail. They cannot friend it, include it, you mention it or refer to it in any way. Doing so violates Abseil's compatibility guidelines and may result in breakage. See https://abseil.io/about/compatibility for more information.

The following cases will result in warnings:

absl::strings_internal::foo();
// warning triggered on this line
class foo {
  friend struct absl::container_internal::faa;
  // warning triggered on this line
};
absl::memory_internal::MakeUniqueResult();
// warning triggered on this line

Ensures code does not open namespace absl as that violates Abseil's compatibility guidelines. Code should not open namespace absl as that conflicts with Abseil's compatibility guidelines and may result in breakage.

Any code that uses:

namespace absl {
 ...
}

will be prompted with a warning.

See the full Abseil compatibility guidelines for more information.

Suggests removal of unnecessary calls to absl::StrCat when the result is being passed to another call to absl::StrCat or absl::StrAppend.

The extra calls cause unnecessary temporary strings to be constructed. Removing them makes the code smaller and faster.

Examples:

std::string s = absl::StrCat("A", absl::StrCat("B", absl::StrCat("C", "D")));
//before

std::string s = absl::StrCat("A", "B", "C", "D");
//after

absl::StrAppend(&s, absl::StrCat("E", "F", "G"));
//before

absl::StrAppend(&s, "E", "F", "G");
//after

Flags uses of absl::StrCat() to append to a std::string. Suggests absl::StrAppend() should be used instead.

The extra calls cause unnecessary temporary strings to be constructed. Removing them makes the code smaller and faster.

a = absl::StrCat(a, b); // Use absl::StrAppend(&a, b) instead.

Does not diagnose cases where absl::StrCat() is used as a template argument for a functor.

Checks whether a std::string::find() or std::string::rfind() (and corresponding std::string_view methods) result is compared with 0, and suggests replacing with absl::StartsWith(). This is both a readability and performance issue.

starts_with was added as a built-in function on those types in C++20. If available, prefer enabling modernize-use-starts-ends-with instead of this check.

string s = "...";
if (s.find("Hello World") == 0) { /* do something */ }
if (s.rfind("Hello World", 0) == 0) { /* do something */ }

becomes

string s = "...";
if (absl::StartsWith(s, "Hello World")) { /* do something */ }
if (absl::StartsWith(s, "Hello World")) { /* do something */ }

StringLikeClasses

Semicolon-separated list of names of string-like classes. By default both std::basic_string and std::basic_string_view are considered. The list of methods to be considered is fixed.

IncludeStyle

A string specifying which include-style is used, llvm or google. Default is llvm.

AbseilStringsMatchHeader

The location of Abseil's strings/match.h. Defaults to absl/strings/match.h.

Finds s.find(...) == string::npos comparisons (for various string-like types) and suggests replacing with absl::StrContains().

This improves readability and reduces the likelihood of accidentally mixing find() and npos from different string-like types.

By default, "string-like types" includes ::std::basic_string, ::std::basic_string_view, and ::absl::string_view. See the StringLikeClasses option to change this.

std::string s = "...";
if (s.find("Hello World") == std::string::npos) { /* do something */ }

absl::string_view a = "...";
if (absl::string_view::npos != a.find("Hello World")) { /* do something */ }

becomes

std::string s = "...";
if (!absl::StrContains(s, "Hello World")) { /* do something */ }

absl::string_view a = "...";
if (absl::StrContains(a, "Hello World")) { /* do something */ }

StringLikeClasses

Semicolon-separated list of names of string-like classes. By default includes ::std::basic_string, ::std::basic_string_view, and ::absl::string_view.

IncludeStyle

A string specifying which include-style is used, llvm or google. Default is llvm.

AbseilStringsMatchHeader

The location of Abseil's strings/match.h. Defaults to absl/strings/match.h.

Prefer comparisons in the absl::Time domain instead of the integer domain.

N.B.: In cases where an absl::Time is being converted to an integer, alignment may occur. If the comparison depends on this alignment, doing the comparison in the absl::Time domain may yield a different result. In practice this is very rare, and still indicates a bug which should be fixed.

Examples:

// Original - Comparison in the integer domain
int x;
absl::Time t;
if (x < absl::ToUnixSeconds(t)) ...

// Suggested - Compare in the absl::Time domain instead
if (absl::FromUnixSeconds(x) < t) ...

Finds and fixes absl::Time subtraction expressions to do subtraction in the Time domain instead of the numeric domain.

There are two cases of Time subtraction in which deduce additional type information:

• When the result is an absl::Duration and the first argument is an absl::Time.
• When the second argument is a absl::Time.

In the first case, we must know the result of the operation, since without that the second operand could be either an absl::Time or an absl::Duration. In the second case, the first operand must be an absl::Time, because subtracting an absl::Time from an absl::Duration is not defined.

Examples:

int x;
absl::Time t;

// Original - absl::Duration result and first operand is an absl::Time.
absl::Duration d = absl::Seconds(absl::ToUnixSeconds(t) - x);

// Suggestion - Perform subtraction in the Time domain instead.
absl::Duration d = t - absl::FromUnixSeconds(x);


// Original - Second operand is an absl::Time.
int i = x - absl::ToUnixSeconds(t);

// Suggestion - Perform subtraction in the Time domain instead.
int i = absl::ToInt64Seconds(absl::FromUnixSeconds(x) - t);

Finds calls to absl::Duration arithmetic operators and factories whose argument needs an explicit cast to continue compiling after upcoming API changes.

The operators *=, /=, *, and / for absl::Duration currently accept an argument of class type that is convertible to an arithmetic type. Such a call currently converts the value to an int64_t, even in a case such as std::atomic<float> that would result in lossy conversion.

Additionally, the absl::Duration factory functions (absl::Hours, absl::Minutes, etc) currently accept an int64_t or a floating-point type. Similar to the arithmetic operators, calls with an argument of class type that is convertible to an arithmetic type go through the int64_t path.

These operators and factories will be changed to only accept arithmetic types to prevent unintended behavior. After these changes are released, passing an argument of class type will no longer compile, even if the type is implicitly convertible to an arithmetic type.

Here are example fixes created by this check:

std::atomic<int> a;
absl::Duration d = absl::Milliseconds(a);
d *= a;

becomes

std::atomic<int> a;
absl::Duration d = absl::Milliseconds(static_cast<int64_t>(a));
d *= static_cast<int64_t>(a);

Note that this check always adds a cast to int64_t in order to preserve the current behavior of user code. It is possible that this uncovers unintended behavior due to types implicitly convertible to a floating-point type.

Finds ID-dependent variables and fields that are used within loops. This causes branches to occur inside the loops, and thus leads to performance degradation.

// The following code will produce a warning because this ID-dependent
// variable is used in a loop condition statement.
int ThreadID = get_local_id(0);

// The following loop will produce a warning because the loop condition
// statement depends on an ID-dependent variable.
for (int i = 0; i < ThreadID; ++i) {
  std::cout << i << std::endl;
}

// The following loop will not produce a warning, because the ID-dependent
// variable is not used in the loop condition statement.
for (int i = 0; i < 100; ++i) {
  std::cout << ThreadID << std::endl;
}

Based on the Altera SDK for OpenCL: Best Practices Guide.

Finds kernel files and include directives whose filename is kernel.cl, Verilog.cl, or VHDL.cl. The check is case insensitive.

Such kernel file names cause the offline compiler to generate intermediate design files that have the same names as certain internal files, which leads to a compilation error.

Based on the Guidelines for Naming the Kernel section in the Intel FPGA SDK for OpenCL Pro Edition: Programming Guide.

Finds OpenCL kernel functions that call a barrier function but do not call an ID function (get_local_id, get_local_id, get_group_id, or get_local_linear_id).

These kernels may be viable single work-item kernels, but will be forced to execute as NDRange kernels if using a newer version of the Altera Offline Compiler (>= v17.01).

If using an older version of the Altera Offline Compiler, these kernel functions will be treated as single work-item kernels, which could be inefficient or lead to errors if NDRange semantics were intended.

Based on the Altera SDK for OpenCL: Best Practices Guide.

Examples:

// error: function calls barrier but does not call an ID function.
void __kernel barrier_no_id(__global int * foo, int size) {
  for (int i = 0; i < 100; i++) {
    foo[i] += 5;
  }
  barrier(CLK_GLOBAL_MEM_FENCE);
}

// ok: function calls barrier and an ID function.
void __kernel barrier_with_id(__global int * foo, int size) {
  for (int i = 0; i < 100; i++) {
    int tid = get_global_id(0);
    foo[tid] += 5;
  }
  barrier(CLK_GLOBAL_MEM_FENCE);
}

// ok with AOC Version 17.01: the reqd_work_group_size turns this into
// an NDRange.
__attribute__((reqd_work_group_size(2,2,2)))
void __kernel barrier_with_id(__global int * foo, int size) {
  for (int i = 0; i < 100; i++) {
    foo[tid] += 5;
  }
  barrier(CLK_GLOBAL_MEM_FENCE);
}

AOCVersion

Defines the version of the Altera Offline Compiler. Defaults to 1600 (corresponding to version 16.00).

Finds structs that are inefficiently packed or aligned, and recommends packing and/or aligning of said structs as needed.

Structs that are not packed take up more space than they should, and accessing structs that are not well aligned is inefficient.

Fix-its are provided to fix both of these issues by inserting and/or amending relevant struct attributes.

Based on the Altera SDK for OpenCL: Best Practices Guide.

// The following struct is originally aligned to 4 bytes, and thus takes up
// 12 bytes of memory instead of 10. Packing the struct will make it use
// only 10 bytes of memory, and aligning it to 16 bytes will make it
// efficient to access.
struct example {
  char a;    // 1 byte
  double b;  // 8 bytes
  char c;    // 1 byte
};

// The following struct is arranged in such a way that packing is not needed.
// However, it is aligned to 4 bytes instead of 8, and thus needs to be
// explicitly aligned.
struct implicitly_packed_example {
  char a;  // 1 byte
  char b;  // 1 byte
  char c;  // 1 byte
  char d;  // 1 byte
  int e;   // 4 bytes
};

// The following struct is explicitly aligned and packed.
struct good_example {
  char a;    // 1 byte
  double b;  // 8 bytes
  char c;    // 1 byte
} __attribute__((packed)) __attribute__((aligned(16));

// Explicitly aligning a struct to the wrong value will result in a warning.
// The following example should be aligned to 16 bytes, not 32.
struct badly_aligned_example {
  char a;    // 1 byte
  double b;  // 8 bytes
  char c;    // 1 byte
} __attribute__((packed)) __attribute__((aligned(32)));

Finds inner loops that have not been unrolled, as well as fully unrolled loops with unknown loop bounds or a large number of iterations.

Unrolling inner loops could improve the performance of OpenCL kernels. However, if they have unknown loop bounds or a large number of iterations, they cannot be fully unrolled, and should be partially unrolled.

Notes:

• This check is unable to determine the number of iterations in a while or do..while loop; hence if such a loop is fully unrolled, a note is emitted advising the user to partially unroll instead.
• In for loops, our check only works with simple arithmetic increments ( +, -, *, /). For all other increments, partial unrolling is advised.
• Depending on the exit condition, the calculations for determining if the number of iterations is large may be off by 1. This should not be an issue since the cut-off is generally arbitrary.

Based on the Altera SDK for OpenCL: Best Practices Guide.

for (int i = 0; i < 10; i++) {  // ok: outer loops should not be unrolled
   int j = 0;
   do {  // warning: this inner do..while loop should be unrolled
      j++;
   } while (j < 15);

   int k = 0;
   #pragma unroll
   while (k < 20) {  // ok: this inner loop is already unrolled
      k++;
   }
}

int A[1000];
#pragma unroll
// warning: this loop is large and should be partially unrolled
for (int a : A) {
   printf("%d", a);
}

#pragma unroll 5
// ok: this loop is large, but is partially unrolled
for (int a : A) {
   printf("%d", a);
}

#pragma unroll
// warning: this loop is large and should be partially unrolled
for (int i = 0; i < 1000; ++i) {
   printf("%d", i);
}

#pragma unroll 5
// ok: this loop is large, but is partially unrolled
for (int i = 0; i < 1000; ++i) {
   printf("%d", i);
}

#pragma unroll
// warning: << operator not supported, recommend partial unrolling
for (int i = 0; i < 1000; i<<1) {
   printf("%d", i);
}

std::vector<int> someVector (100, 0);
int i = 0;
#pragma unroll
// note: loop may be large, recommend partial unrolling
while (i < someVector.size()) {
   someVector[i]++;
}

#pragma unroll
// note: loop may be large, recommend partial unrolling
while (true) {
   printf("In loop");
}

#pragma unroll 5
// ok: loop may be large, but is partially unrolled
while (i < someVector.size()) {
   someVector[i]++;
}

MaxLoopIterations

Defines the maximum number of loop iterations that a fully unrolled loop can have. By default, it is set to 100.

In practice, this refers to the integer value of the upper bound within the loop statement's condition expression.

The usage of accept() is not recommended, it's better to use accept4(). Without this flag, an opened sensitive file descriptor would remain open across a fork+exec to a lower-privileged SELinux domain.

Examples:

accept(sockfd, addr, addrlen);

// becomes

accept4(sockfd, addr, addrlen, SOCK_CLOEXEC);

accept4() should include SOCK_CLOEXEC in its type argument to avoid the file descriptor leakage. Without this flag, an opened sensitive file would remain open across a fork+exec to a lower-privileged SELinux domain.

Examples:

accept4(sockfd, addr, addrlen, SOCK_NONBLOCK);

// becomes

accept4(sockfd, addr, addrlen, SOCK_NONBLOCK | SOCK_CLOEXEC);

The usage of creat() is not recommended, it's better to use open().

Examples:

int fd = creat(path, mode);

// becomes

int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, mode);

The usage of dup() is not recommended, it's better to use fcntl(), which can set the close-on-exec flag. Otherwise, an opened sensitive file would remain open across a fork+exec to a lower-privileged SELinux domain.

Examples:

int fd = dup(oldfd);

// becomes

int fd = fcntl(oldfd, F_DUPFD_CLOEXEC);

The usage of epoll_create() is not recommended, it's better to use epoll_create1(), which allows close-on-exec.

Examples:

epoll_create(size);

// becomes

epoll_create1(EPOLL_CLOEXEC);

epoll_create1() should include EPOLL_CLOEXEC in its type argument to avoid the file descriptor leakage. Without this flag, an opened sensitive file would remain open across a fork+exec to a lower-privileged SELinux domain.

Examples:

epoll_create1(0);

// becomes

epoll_create1(EPOLL_CLOEXEC);

fopen() should include e in their mode string; so re would be valid. This is equivalent to having set FD_CLOEXEC on that descriptor.

Examples:

fopen("fn", "r");

// becomes

fopen("fn", "re");

The usage of inotify_init() is not recommended, it's better to use inotify_init1().

Examples:

inotify_init();

// becomes

inotify_init1(IN_CLOEXEC);

inotify_init1() should include IN_CLOEXEC in its type argument to avoid the file descriptor leakage. Without this flag, an opened sensitive file would remain open across a fork+exec to a lower-privileged SELinux domain.

Examples:

inotify_init1(IN_NONBLOCK);

// becomes

inotify_init1(IN_NONBLOCK | IN_CLOEXEC);

memfd_create() should include MFD_CLOEXEC in its type argument to avoid the file descriptor leakage. Without this flag, an opened sensitive file would remain open across a fork+exec to a lower-privileged SELinux domain.

Examples:

memfd_create(name, MFD_ALLOW_SEALING);

// becomes

memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);

A common source of security bugs is code that opens a file without using the O_CLOEXEC flag. Without that flag, an opened sensitive file would remain open across a fork+exec to a lower-privileged SELinux domain, leaking that sensitive data. Open-like functions including open(), openat(), and open64() should include O_CLOEXEC in their flags argument.

Examples:

open("filename", O_RDWR);
open64("filename", O_RDWR);
openat(0, "filename", O_RDWR);

// becomes

open("filename", O_RDWR | O_CLOEXEC);
open64("filename", O_RDWR | O_CLOEXEC);
openat(0, "filename", O_RDWR | O_CLOEXEC);

This check detects usage of pipe(). Using pipe() is not recommended, pipe2() is the suggested replacement. The check also adds the O_CLOEXEC flag that marks the file descriptor to be closed in child processes. Without this flag a sensitive file descriptor can be leaked to a child process, potentially into a lower-privileged SELinux domain.

Examples:

pipe(pipefd);

Suggested replacement:

pipe2(pipefd, O_CLOEXEC);

This check ensures that pipe2() is called with the O_CLOEXEC flag. The check also adds the O_CLOEXEC flag that marks the file descriptor to be closed in child processes. Without this flag a sensitive file descriptor can be leaked to a child process, potentially into a lower-privileged SELinux domain.

Examples:

pipe2(pipefd, O_NONBLOCK);

Suggested replacement:

pipe2(pipefd, O_NONBLOCK | O_CLOEXEC);

socket() should include SOCK_CLOEXEC in its type argument to avoid the file descriptor leakage. Without this flag, an opened sensitive file would remain open across a fork+exec to a lower-privileged SELinux domain.

Examples:

socket(domain, type, SOCK_STREAM);

// becomes

socket(domain, type, SOCK_STREAM | SOCK_CLOEXEC);

Diagnoses comparisons that appear to be incorrectly placed in the argument to the TEMP_FAILURE_RETRY macro. Having such a use is incorrect in the vast majority of cases, and will often silently defeat the purpose of the TEMP_FAILURE_RETRY macro.

For context, TEMP_FAILURE_RETRY is a convenience macro provided by both glibc and Bionic. Its purpose is to repeatedly run a syscall until it either succeeds, or fails for reasons other than being interrupted.

Example buggy usage looks like:

char cs[1];
while (TEMP_FAILURE_RETRY(read(STDIN_FILENO, cs, sizeof(cs)) != 0)) {
  // Do something with cs.
}

Because TEMP_FAILURE_RETRY will check for whether the result of the comparison is -1, and retry if so.

If you encounter this, the fix is simple: lift the comparison out of the TEMP_FAILURE_RETRY argument, like so:

char cs[1];
while (TEMP_FAILURE_RETRY(read(STDIN_FILENO, cs, sizeof(cs))) != 0) {
  // Do something with cs.
}

RetryMacros

A comma-separated list of the names of retry macros to be checked.

Detects calls to standard library iterator algorithms that could be replaced with a Boost ranges version instead.

auto Iter1 = std::find(Items.begin(), Items.end(), 0);
auto AreSame = std::equal(Items1.cbegin(), Items1.cend(), std::begin(Items2),
                          std::end(Items2));

Transforms to:

auto Iter1 = boost::range::find(Items, 0);
auto AreSame = boost::range::equal(Items1, Items2);

Calls to the following std library algorithms are checked:

std::accumulate, std::adjacent_difference, std::adjacent_find, std::all_of, std::any_of, std::binary_search, std::copy_backward, std::copy_if, std::copy, std::count_if, std::count, std::equal_range, std::equal, std::fill, std::find_end, std::find_first_of, std::find_if_not, std::find_if, std::find, std::for_each, std::generate, std::includes, std::iota, std::is_partitioned, std::is_permutation, std::is_sorted_until, std::is_sorted, std::lexicographical_compare, std::lower_bound, std::make_heap, std::max_element, std::merge, std::min_element, std::mismatch, std::next_permutation, std::none_of, std::parital_sum, std::partial_sort_copy, std::partition_copy, std::partition_point, std::partition, std::pop_heap, std::prev_permutation, std::push_heap, std::random_shuffle, std::reduce, std::remove_copy_if, std::remove_copy, std::remove_if, std::remove, std::replace_copy_if, std::replace_copy, std::replace_if, std::replace, std::reverse_copy, std::reverse, std::search, std::set_difference, std::set_intersection, std::set_symmetric_difference, std::set_union, std::sort_heap, std::sort, std::stable_partition, std::stable_sort, std::transform, std::unique_copy, std::unique, std::upper_bound.

The check will also look for the following functions from the boost::algorithm namespace:

all_of_equal, any_of_equal, any_of, apply_permutation, apply_reverse_permutation, clamp_range, copy_if_until, copy_if_while, copy_if, copy_until, copy_while, find_backward, find_if_backward, find_if_not_backward, find_if_not, find_not_backward, hex_lower, hex, iota, all_of, is_decreasing, is_increasing, is_palindrome, is_partitioned_until, is_partitioned, is_permutation, is_sorted_until, is_sorted, is_strictly_decreasing, is_strictly_increasing, none_of_equal, none_of, one_of_equal, one_of, partition_copy, partition_point, reduce, unhex.

If calls are made using reverse iterators on containers, The code will be fixed using the boost::adaptors::reverse adaptor.

auto AreSame = std::equal(Items1.rbegin(), Items1.rend(),
                          std::crbegin(Items2), std::crend(Items2));

Transforms to:

auto AreSame = boost::range::equal(boost::adaptors::reverse(Items1),
                                   boost::adaptors::reverse(Items2));

IncludeStyle

A string specifying which include-style is used, llvm or google. Default is llvm.

IncludeBoostSystem

If true (default value) the boost headers are included as system headers with angle brackets (#include <boost.hpp>), otherwise quotes are used (#include "boost.hpp").

UseReversePipe

When true (default false), fixes which involve reverse ranges will use the pipe adaptor syntax instead of the function syntax.

std::find(Items.rbegin(), Items.rend(), 0);

Transforms to:

boost::range::find(Items | boost::adaptors::reversed, 0);

This check finds conversion from integer type like int to std::string or std::wstring using boost::lexical_cast, and replace it with calls to std::to_string and std::to_wstring.

It doesn't replace conversion from floating points despite the to_string overloads, because it would change the behavior.

auto str = boost::lexical_cast<std::string>(42);
auto wstr = boost::lexical_cast<std::wstring>(2137LL);

// Will be changed to
auto str = std::to_string(42);
auto wstr = std::to_wstring(2137LL);

Checks that argument comments match parameter names.

The check understands argument comments in the form /*parameter_name=*/ that are placed right before the argument.

void f(bool foo);

...

f(/*bar=*/true);
// warning: argument name 'bar' in comment does not match parameter name 'foo'

The check tries to detect typos and suggest automated fixes for them.

StrictMode

When false (default value), the check will ignore leading and trailing underscores and case when comparing names -- otherwise they are taken into account.

IgnoreSingleArgument

When true, the check will ignore the single argument.

CommentBoolLiterals

When true, the check will add argument comments in the format /*ParameterName=*/ right before the boolean literal argument.

Before:

void foo(bool TurnKey, bool PressButton);

foo(true, false);

After:

void foo(bool TurnKey, bool PressButton);

foo(/*TurnKey=*/true, /*PressButton=*/false);

CommentIntegerLiterals

When true, the check will add argument comments in the format /*ParameterName=*/ right before the integer literal argument.

Before:

void foo(int MeaningOfLife);

foo(42);

After:

void foo(int MeaningOfLife);

foo(/*MeaningOfLife=*/42);

CommentFloatLiterals

When true, the check will add argument comments in the format /*ParameterName=*/ right before the float/double literal argument.

Before:

void foo(float Pi);

foo(3.14159);

After:

void foo(float Pi);

foo(/*Pi=*/3.14159);

CommentStringLiterals

When true, the check will add argument comments in the format /*ParameterName=*/ right before the string literal argument.

Before:

void foo(const char *String);
void foo(const wchar_t *WideString);

foo("Hello World");
foo(L"Hello World");

After:

void foo(const char *String);
void foo(const wchar_t *WideString);

foo(/*String=*/"Hello World");
foo(/*WideString=*/L"Hello World");

CommentCharacterLiterals

When true, the check will add argument comments in the format /*ParameterName=*/ right before the character literal argument.

Before:

void foo(char *Character);

foo('A');

After:

void foo(char *Character);

foo(/*Character=*/'A');

CommentUserDefinedLiterals

When true, the check will add argument comments in the format /*ParameterName=*/ right before the user defined literal argument.

Before:

void foo(double Distance);

double operator"" _km(long double);

foo(402.0_km);

After:

void foo(double Distance);

double operator"" _km(long double);

foo(/*Distance=*/402.0_km);

CommentNullPtrs

When true, the check will add argument comments in the format /*ParameterName=*/ right before the nullptr literal argument.

Before:

void foo(A* Value);

foo(nullptr);

After:

void foo(A* Value);

foo(/*Value=*/nullptr);

Finds assert() with side effect.

The condition of assert() is evaluated only in debug builds so a condition with side effect can cause different behavior in debug / release builds.

AssertMacros

A comma-separated list of the names of assert macros to be checked.

CheckFunctionCalls

Whether to treat non-const member and non-member functions as they produce side effects. Disabled by default because it can increase the number of false positive warnings.

IgnoredFunctions

A semicolon-separated list of the names of functions or methods to be considered as not having side-effects. Regular expressions are accepted, e.g. [Rr]ef(erence)?$ matches every type with suffix Ref, ref, Reference and reference. The default is empty. If a name in the list contains the sequence :: it is matched against the qualified typename (i.e. namespace::Type, otherwise it is matched against only the type name (i.e. Type).

Finds assignments within conditions of if statements. Such assignments are bug-prone because they may have been intended as equality tests.

This check finds all assignments within if conditions, including ones that are not flagged by -Wparentheses due to an extra set of parentheses, and including assignments that call an overloaded operator=(). The identified assignments violate BARR group "Rule 8.2.c".

int f = 3;
if(f = 4) { // This is identified by both `Wparentheses` and this check - should it have been: `if (f == 4)` ?
  f = f + 1;
}

if((f == 5) || (f = 6)) { // the assignment here `(f = 6)` is identified by this check, but not by `-Wparentheses`. Should it have been `(f == 6)` ?
  f = f + 2;
}

Finds pthread_kill function calls when a thread is terminated by raising SIGTERM signal and the signal kills the entire process, not just the individual thread. Use any signal except SIGTERM.

pthread_kill(thread, SIGTERM);

This check corresponds to the CERT C Coding Standard rule POS44-C. Do not use signals to terminate threads.

cert-pos44-c redirects here as an alias of this check.

Checks for conditions based on implicit conversion from a bool pointer to bool.

Example:

bool *p;
if (p) {
  // Never used in a pointer-specific way.
}

Checks for repeated branches in if/else if/else chains, consecutive repeated branches in switch statements and identical true and false branches in conditional operators.

if (test_value(x)) {
  y++;
  do_something(x, y);
} else {
  y++;
  do_something(x, y);
}

In this simple example (which could arise e.g. as a copy-paste error) the then and else branches are identical and the code is equivalent the following shorter and cleaner code:

test_value(x); // can be omitted unless it has side effects
y++;
do_something(x, y);

If this is the intended behavior, then there is no reason to use a conditional statement; otherwise the issue can be solved by fixing the branch that is handled incorrectly.

The check also detects repeated branches in longer if/else if/else chains where it would be even harder to notice the problem.

In switch statements the check only reports repeated branches when they are consecutive, because it is relatively common that the case: labels have some natural ordering and rearranging them would decrease the readability of the code. For example:

switch (ch) {
case 'a':
  return 10;
case 'A':
  return 10;
case 'b':
  return 11;
case 'B':
  return 11;
default:
  return 10;
}

Here the check reports that the 'a' and 'A' branches are identical (and that the 'b' and 'B' branches are also identical), but does not report that the default: branch is also identical to the first two branches. If this is indeed the correct behavior, then it could be implemented as:

switch (ch) {
case 'a':
case 'A':
  return 10;
case 'b':
case 'B':
  return 11;
default:
  return 10;
}

Here the check does not warn for the repeated return 10;, which is good if we want to preserve that 'a' is before 'b' and default: is the last branch.

Switch cases marked with the [[fallthrough]] attribute are ignored.

Finally, the check also examines conditional operators and reports code like:

return test_value(x) ? x : x;

Unlike if statements, the check does not detect chains of conditional operators.

Note: This check also reports situations where branches become identical only after preprocessing.

Detects unsafe or redundant two-step casting operations involving void*.

Two-step type conversions via void* are discouraged for several reasons.

• They obscure code and impede its understandability, complicating maintenance.
• These conversions bypass valuable compiler support, erasing warnings related to pointer alignment. It may violate strict aliasing rule and leading to undefined behavior.
• In scenarios involving multiple inheritance, ambiguity and unexpected outcomes can arise due to the loss of type information, posing runtime issues.

In summary, avoiding two-step type conversions through void* ensures clearer code, maintains essential compiler warnings, and prevents ambiguity and potential runtime errors, particularly in complex inheritance scenarios.

Examples:

using IntegerPointer = int *;
double *ptr;

static_cast<IntegerPointer>(static_cast<void *>(ptr)); // WRONG
reinterpret_cast<IntegerPointer>(reinterpret_cast<void *>(ptr)); // WRONG
(IntegerPointer)(void *)ptr; // WRONG
IntegerPointer(static_cast<void *>(ptr)); // WRONG

Check detects chained comparison operators that can lead to unintended behavior or logical errors.

Chained comparisons are expressions that use multiple comparison operators to compare three or more values. For example, the expression a < b < c compares the values of a, b, and c. However, this expression does not evaluate as (a < b) && (b < c), which is probably what the developer intended. Instead, it evaluates as (a < b) < c, which may produce unintended results, especially when the types of a, b, and c are different.

To avoid such errors, the check will issue a warning when a chained comparison operator is detected, suggesting to use parentheses to specify the order of evaluation or to use a logical operator to separate comparison expressions.

Consider the following examples:

int a = 2, b = 6, c = 4;
if (a < b < c) {
    // This block will be executed
}

In this example, the developer intended to check if a is less than b and b is less than c. However, the expression a < b < c is equivalent to (a < b) < c. Since a < b is true, the expression (a < b) < c is evaluated as 1 < c, which is equivalent to true < c and is invalid in this case as b < c is false.

Even that above issue could be detected as comparison of int to bool, there is more dangerous example:

bool a = false, b = false, c = true;
if (a == b == c) {
    // This block will be executed
}

In this example, the developer intended to check if a, b, and c are all equal. However, the expression a == b == c is evaluated as (a == b) == c. Since a == b is true, the expression (a == b) == c is evaluated as true == c, which is equivalent to true == true. This comparison yields true, even though a and b are false, and are not equal to c.

To avoid this issue, the developer can use a logical operator to separate the comparison expressions, like this:

if (a == b && b == c) {
    // This block will not be executed
}

Alternatively, use of parentheses in the comparison expressions can make the developer's intention more explicit and help avoid misunderstanding.

if ((a == b) == c) {
    // This block will be executed
}

Detects unspecified behavior about equality comparison between pointer to member virtual function and anything other than null-pointer-constant.

struct A {
  void f1();
  void f2();
  virtual void f3();
  virtual void f4();

  void g1(int);
};

void fn() {
  bool r1 = (&A::f1 == &A::f2);  // ok
  bool r2 = (&A::f1 == &A::f3);  // bugprone
  bool r3 = (&A::f1 != &A::f3);  // bugprone
  bool r4 = (&A::f3 == nullptr); // ok
  bool r5 = (&A::f3 == &A::f4);  // bugprone

  void (A::*v1)() = &A::f3;
  bool r6 = (v1 == &A::f1); // bugprone
  bool r6 = (v1 == nullptr); // ok

  void (A::*v2)() = &A::f2;
  bool r7 = (v2 == &A::f1); // false positive, but potential risk if assigning other value to v2.

  void (A::*v3)(int) = &A::g1;
  bool r8 = (v3 == &A::g1); // ok, no virtual function match void(A::*)(int) signature.
}

Provide warnings on equality comparisons involve pointers to member virtual function or variables which is potential pointer to member virtual function and any entity other than a null-pointer constant.

In certain compilers, virtual function addresses are not conventional pointers but instead consist of offsets and indexes within a virtual function table (vtable). Consequently, these pointers may vary between base and derived classes, leading to unpredictable behavior when compared directly. This issue becomes particularly challenging when dealing with pointers to pure virtual functions, as they may not even have a valid address, further complicating comparisons.

Instead, it is recommended to utilize the typeid operator or other appropriate mechanisms for comparing objects to ensure robust and predictable behavior in your codebase. By heeding this detection and adopting a more reliable comparison method, you can mitigate potential issues related to unspecified behavior, especially when dealing with pointers to member virtual functions or pure virtual functions, thereby improving the overall stability and maintainability of your code. In scenarios involving pointers to member virtual functions, it's only advisable to employ nullptr for comparisons.

Does not analyze values stored in a variable. For variable, only analyze all virtual methods in the same class or struct and diagnose when assigning a pointer to member virtual function to this variable is possible.

Finds copy constructors where the constructor doesn't call the copy constructor of the base class.

class Copyable {
public:
  Copyable() = default;
  Copyable(const Copyable &) = default;

  int memberToBeCopied = 0;
};

class X2 : public Copyable {
  X2(const X2 &other) {} // Copyable(other) is missing
};

Also finds copy constructors where the constructor of the base class don't have parameter.

class X3 : public Copyable {
  X3(const X3 &other) : Copyable() {} // other is missing
};

Failure to properly initialize base class sub-objects during copy construction can result in undefined behavior, crashes, data corruption, or other unexpected outcomes. The check ensures that the copy constructor of a derived class properly calls the copy constructor of the base class, helping to prevent bugs and improve code quality.

Limitations:

• It won't generate warnings for empty classes, as there are no class members (including base class sub-objects) to worry about.
• It won't generate warnings for base classes that have copy constructor private or deleted.
• It won't generate warnings for base classes that are initialized using other non-default constructor, as this could be intentional.

The check also suggests a fix-its in some cases.

Detects error-prone Curiously Recurring Template Pattern usage, when the CRTP can be constructed outside itself and the derived class.

The CRTP is an idiom, in which a class derives from a template class, where itself is the template argument. It should be ensured that if a class is intended to be a base class in this idiom, it can only be instantiated if the derived class is it's template argument.

Example:

template <typename T> class CRTP {
private:
  CRTP() = default;
  friend T;
};

class Derived : CRTP<Derived> {};

Below can be seen some common mistakes that will allow the breaking of the idiom.

If the constructor of a class intended to be used in a CRTP is public, then it allows users to construct that class on its own.

Example:

template <typename T> class CRTP {
public:
  CRTP() = default;
};

class Good : CRTP<Good> {};
Good GoodInstance;

CRTP<int> BadInstance;

If the constructor is protected, the possibility of an accidental instantiation is prevented, however it can fade an error, when a different class is used as the template parameter instead of the derived one.

Example:

template <typename T> class CRTP {
protected:
  CRTP() = default;
};

class Good : CRTP<Good> {};
Good GoodInstance;

class Bad : CRTP<Good> {};
Bad BadInstance;

To ensure that no accidental instantiation happens, the best practice is to make the constructor private and declare the derived class as friend. Note that as a tradeoff, this also gives the derived class access to every other private members of the CRTP.

Example:

template <typename T> class CRTP {
  CRTP() = default;
  friend T;
};

class Good : CRTP<Good> {};
Good GoodInstance;

class Bad : CRTP<Good> {};
Bad CompileTimeError;

CRTP<int> AlsoCompileTimeError;

Limitations:

• The check is not supported below C++11
• The check does not handle when the derived class is passed as a variadic template argument
• Accessible functions that can construct the CRTP, like factory functions are not checked

The check also suggests a fix-its in some cases.

Detect dangling references in value handles like std::string_view. These dangling references can be a result of constructing handles from temporary values, where the temporary is destroyed soon after the handle is created.

Examples:

string_view View = string();  // View will dangle.
string A;
View = A + "A";  // still dangle.

vector<string_view> V;
V.push_back(string());  // V[0] is dangling.
V.resize(3, string());  // V[1] and V[2] will also dangle.

string_view f() {
  // All these return values will dangle.
  return string();
  string S;
  return S;
  char Array[10]{};
  return Array;
}

HandleClasses

A semicolon-separated list of class names that should be treated as handles. By default only std::basic_string_view and std::experimental::basic_string_view are considered.

Finds instances of static variables that are dynamically initialized in header files.

This can pose problems in certain multithreaded contexts. For example, when disabling compiler generated synchronization instructions for static variables initialized at runtime (e.g. by -fno-threadsafe-statics), even if a particular project takes the necessary precautions to prevent race conditions during initialization by providing their own synchronization, header files included from other projects may not. Therefore, such a check is helpful for ensuring that disabling compiler generated synchronization for static variable initialization will not cause problems.

Consider the following code:

int foo() {
  static int k = bar();
  return k;
}

When synchronization of static initialization is disabled, if two threads both call foo for the first time, there is the possibility that k will be double initialized, creating a race condition.

Finds function definitions where parameters of convertible types follow each other directly, making call sites prone to calling the function with swapped (or badly ordered) arguments.

void drawPoint(int X, int Y) { /* ... */ }
FILE *open(const char *Dir, const char *Name, Flags Mode) { /* ... */ }

A potential call like drawPoint(-2, 5) or openPath("a.txt", "tmp", Read) is perfectly legal from the language's perspective, but might not be what the developer of the function intended.

More elaborate and type-safe constructs, such as opaque typedefs or strong types should be used instead, to prevent a mistaken order of arguments.

struct Coord2D { int X; int Y; };
void drawPoint(const Coord2D Pos) { /* ... */ }

FILE *open(const Path &Dir, const Filename &Name, Flags Mode) { /* ... */ }

Due to the potentially elaborate refactoring and API-breaking that is necessary to strengthen the type safety of a project, no automatic fix-its are offered.

Relaxation (or extension) options can be used to broaden the scope of the analysis and fine-tune the enabling of more mixes between types. Some mixes may depend on coding style or preference specific to a project, however, it should be noted that enabling all of these relaxations model the way of mixing at call sites the most. These options are expected to make the check report for more functions, and report longer mixable ranges.

QualifiersMix

Whether to consider parameters of some cvr-qualified T and a differently cvr-qualified T (i.e. T and const T, const T and volatile T, etc.) mixable between one another. If false, the check will consider differently qualified types unmixable. True turns the warnings on. Defaults to false.

The following example produces a diagnostic only if QualifiersMix is enabled:

void *memcpy(const void *Destination, void *Source, std::size_t N) { /* ... */ }

ModelImplicitConversions

Whether to consider parameters of type T and U mixable if there exists an implicit conversion from T to U and U to T. If false, the check will not consider implicitly convertible types for mixability. True turns warnings for implicit conversions on. Defaults to true.

The following examples produce a diagnostic only if ModelImplicitConversions is enabled:

void fun(int Int, double Double) { /* ... */ }
void compare(const char *CharBuf, std::string String) { /* ... */ }

NOTE:

Changing the qualifiers of an expression's type (e.g. from int to const int) is defined as an implicit conversion in the C++ Standard. However, the check separates this decision-making on the mixability of differently qualified types based on whether QualifiersMix was enabled.

For example, the following code snippet will only produce a diagnostic if both QualifiersMix and ModelImplicitConversions are enabled:

void fun2(int Int, const double Double) { /* ... */ }

Filtering options can be used to lessen the size of the diagnostics emitted by the checker, whether the aim is to ignore certain constructs or dampen the noisiness.

MinimumLength

The minimum length required from an adjacent parameter sequence to be diagnosed. Defaults to 2. Might be any positive integer greater or equal to 2. If 0 or 1 is given, the default value 2 will be used instead.

For example, if 3 is specified, the examples above will not be matched.

IgnoredParameterNames

The list of parameter names that should never be considered part of a swappable adjacent parameter sequence. The value is a ;-separated list of names. To ignore unnamed parameters, add "" to the list verbatim (not the empty string, but the two quotes, potentially escaped!). This option is case-sensitive!

By default, the following parameter names, and their Uppercase-initial variants are ignored: "" (unnamed parameters), iterator, begin, end, first, last, lhs, rhs.

IgnoredParameterTypeSuffixes

The list of parameter type name suffixes that should never be considered part of a swappable adjacent parameter sequence. Parameters which type, as written in the source code, end with an element of this option will be ignored. The value is a ;-separated list of names. This option is case-sensitive!

By default, the following, and their lowercase-initial variants are ignored: bool, It, Iterator, InputIt, ForwardIt, BidirIt, RandomIt, random_iterator, ReverseIt, reverse_iterator, reverse_const_iterator, RandomIt, random_iterator, ReverseIt, reverse_iterator, reverse_const_iterator, Const_Iterator, ConstIterator, const_reverse_iterator, ConstReverseIterator. In addition, _Bool (but not _bool) is also part of the default value.

SuppressParametersUsedTogether

Suppresses diagnostics about parameters that are used together or in a similar fashion inside the function's body. Defaults to true. Specifying false will turn off the heuristics.

Currently, the following heuristics are implemented which will suppress the warning about the parameter pair involved:

• The parameters are used in the same expression, e.g. f(a, b) or a < b.

• The parameters are further passed to the same function to the same parameter of that function, of the same overload. E.g. f(a, 1) and f(b, 2) to some f(T, int).

  NOTE:

  The check does not perform path-sensitive analysis, and as such, "same function" in this context means the same function declaration. If the same member function of a type on two distinct instances are called with the parameters, it will still be regarded as "same function".

• The same member field is accessed, or member method is called of the two parameters, e.g. a.foo() and b.foo().
• Separate return statements return either of the parameters on different code paths.

NamePrefixSuffixSilenceDissimilarityTreshold

The number of characters two parameter names might be different on either the head or the tail end with the rest of the name the same so that the warning about the two parameters are silenced. Defaults to 1. Might be any positive integer. If 0, the filtering heuristic based on the parameters' names is turned off.

This option can be used to silence warnings about parameters where the naming scheme indicates that the order of those parameters do not matter.

For example, the parameters LHS and RHS are 1-dissimilar suffixes of each other: L and R is the different character, while HS is the common suffix. Similarly, parameters text1, text2, text3 are 1-dissimilar prefixes of each other, with the numbers at the end being the dissimilar part. If the value is at least 1, such cases will not be reported.

This check is designed to check function signatures!

The check does not investigate functions that are generated by the compiler in a context that is only determined from a call site. These cases include variadic functions, functions in C code that do not have an argument list, and C++ template instantiations. Most of these cases, which are otherwise swappable from a caller's standpoint, have no way of getting "fixed" at the definition point. In the case of C++ templates, only primary template definitions and explicit specializations are matched and analyzed.

None of the following cases produce a diagnostic:

int printf(const char *Format, ...) { /* ... */ }
int someOldCFunction() { /* ... */ }

template <typename T, typename U>
int add(T X, U Y) { return X + Y };

void theseAreNotWarnedAbout() {
    printf("%d %d\n", 1, 2);   // Two ints passed, they could be swapped.
    someOldCFunction(1, 2, 3); // Similarly, multiple ints passed.

    add(1, 2); // Instantiates 'add<int, int>', but that's not a user-defined function.
}

Due to the limitation above, parameters which type are further dependent upon template instantiations to prove that they mix with another parameter's is not diagnosed.

template <typename T>
struct Vector {
  typedef T element_type;
};

// Diagnosed: Explicit instantiation was done by the user, we can prove it
// is the same type.
void instantiated(int A, Vector<int>::element_type B) { /* ... */ }

// Diagnosed: The two parameter types are exactly the same.
template <typename T>
void exact(typename Vector<T>::element_type A,
           typename Vector<T>::element_type B) { /* ... */ }

// Skipped: The two parameters are both 'T' but we cannot prove this
// without actually instantiating.
template <typename T>
void falseNegative(T A, typename Vector<T>::element_type B) { /* ... */ }

In the context of implicit conversions (when ModelImplicitConversions is enabled), the modelling performed by the check warns if the parameters are swappable and the swapped order matches implicit conversions. It does not model whether there exists an unrelated third type from which both parameters can be given in a function call. This means that in the following example, even while strs() clearly carries the possibility to be called with swapped arguments (as long as the arguments are string literals), will not be warned about.

struct String {
    String(const char *Buf);
};

struct StringView {
    StringView(const char *Buf);
    operator const char *() const;
};

// Skipped: Directly swapping expressions of the two type cannot mix.
// (Note: StringView -> const char * -> String would be **two**
// user-defined conversions, which is disallowed by the language.)
void strs(String Str, StringView SV) { /* ... */ }

// Diagnosed: StringView implicitly converts to and from a buffer.
void cStr(StringView SV, const char *Buf() { /* ... */ }

Detects and suggests addressing issues with empty catch statements.

try {
  // Some code that can throw an exception
} catch(const std::exception&) {
}

Having empty catch statements in a codebase can be a serious problem that developers should be aware of. Catch statements are used to handle exceptions that are thrown during program execution. When an exception is thrown, the program jumps to the nearest catch statement that matches the type of the exception.

Empty catch statements, also known as "swallowing" exceptions, catch the exception but do nothing with it. This means that the exception is not handled properly, and the program continues to run as if nothing happened. This can lead to several issues, such as:

• Hidden Bugs: If an exception is caught and ignored, it can lead to hidden bugs that are difficult to diagnose and fix. The root cause of the problem may not be apparent, and the program may continue to behave in unexpected ways.
• Security Issues: Ignoring exceptions can lead to security issues, such as buffer overflows or null pointer dereferences. Hackers can exploit these vulnerabilities to gain access to sensitive data or execute malicious code.
• Poor Code Quality: Empty catch statements can indicate poor code quality and a lack of attention to detail. This can make the codebase difficult to maintain and update, leading to longer development cycles and increased costs.
• Unreliable Code: Code that ignores exceptions is often unreliable and can lead to unpredictable behavior. This can cause frustration for users and erode trust in the software.

To avoid these issues, developers should always handle exceptions properly. This means either fixing the underlying issue that caused the exception or propagating the exception up the call stack to a higher-level handler. If an exception is not important, it should still be logged or reported in some way so that it can be tracked and addressed later.

If the exception is something that can be handled locally, then it should be handled within the catch block. This could involve logging the exception or taking other appropriate action to ensure that the exception is not ignored.

Here is an example:

try {
  // Some code that can throw an exception
} catch (const std::exception& ex) {
  // Properly handle the exception, e.g.:
  std::cerr << "Exception caught: " << ex.what() << std::endl;
}

If the exception cannot be handled locally and needs to be propagated up the call stack, it should be re-thrown or new exception should be thrown.

Here is an example:

try {
  // Some code that can throw an exception
} catch (const std::exception& ex) {
  // Re-throw the exception
  throw;
}

In some cases, catching the exception at this level may not be necessary, and it may be appropriate to let the exception propagate up the call stack. This can be done simply by not using try/catch block.

Here is an example:

void function() {
  // Some code that can throw an exception
}

void callerFunction() {
  try {
    function();
  } catch (const std::exception& ex) {
    // Handling exception on higher level
    std::cerr << "Exception caught: " << ex.what() << std::endl;
  }
}

Other potential solution to avoid empty catch statements is to modify the code to avoid throwing the exception in the first place. This can be achieved by using a different API, checking for error conditions beforehand, or handling errors in a different way that does not involve exceptions. By eliminating the need for try-catch blocks, the code becomes simpler and less error-prone.

Here is an example:

// Old code:
try {
  mapContainer["Key"].callFunction();
} catch(const std::out_of_range&) {
}

// New code
if (auto it = mapContainer.find("Key"); it != mapContainer.end()) {
  it->second.callFunction();
}

In conclusion, empty catch statements are a bad practice that can lead to hidden bugs, security issues, poor code quality, and unreliable code. By handling exceptions properly, developers can ensure that their code is robust, secure, and maintainable.

IgnoreCatchWithKeywords

This option can be used to ignore specific catch statements containing certain keywords. If a catch statement body contains (case-insensitive) any of the keywords listed in this semicolon-separated option, then the catch will be ignored, and no warning will be raised. Default value: @TODO;@FIXME.

AllowEmptyCatchForExceptions

This option can be used to ignore empty catch statements for specific exception types. By default, the check will raise a warning if an empty catch statement is detected, regardless of the type of exception being caught. However, in certain situations, such as when a developer wants to intentionally ignore certain exceptions or handle them in a different way, it may be desirable to allow empty catch statements for specific exception types. To configure this option, a semicolon-separated list of exception type names should be provided. If an exception type name in the list is caught in an empty catch statement, no warning will be raised. Default value: empty string.

Finds functions which may throw an exception directly or indirectly, but they should not. The functions which should not throw exceptions are the following:

• Destructors
• Move constructors
• Move assignment operators
• The main() functions
• swap() functions
• iter_swap() functions
• iter_move() functions
• Functions marked with throw() or noexcept
• Other functions given as option

A destructor throwing an exception may result in undefined behavior, resource leaks or unexpected termination of the program. Throwing move constructor or move assignment also may result in undefined behavior or resource leak. The swap() operations expected to be non throwing most of the cases and they are always possible to implement in a non throwing way. Non throwing swap() operations are also used to create move operations. A throwing main() function also results in unexpected termination.

Functions declared explicitly with noexcept(false) or throw(exception) will be excluded from the analysis, as even though it is not recommended for functions like swap(), main(), move constructors, move assignment operators and destructors, it is a clear indication of the developer's intention and should be respected.

WARNING! This check may be expensive on large source files.

FunctionsThatShouldNotThrow

Comma separated list containing function names which should not throw. An example value for this parameter can be WinMain which adds function WinMain() in the Windows API to the list of the functions which should not throw. Default value is an empty string.

IgnoredExceptions

Comma separated list containing type names which are not counted as thrown exceptions in the check. Default value is an empty string.

The check flags type mismatches in folds like std::accumulate that might result in loss of precision. std::accumulate folds an input range into an initial value using the type of the latter, with operator+ by default. This can cause loss of precision through:

• Truncation: The following code uses a floating point range and an int initial value, so truncation will happen at every application of operator+ and the result will be 0, which might not be what the user expected.

  auto a = {0.5f, 0.5f, 0.5f, 0.5f};
  return std::accumulate(std::begin(a), std::end(a), 0);

• Overflow: The following code also returns 0.

  auto a = {65536LL * 65536 * 65536};
  return std::accumulate(std::begin(a), std::end(a), 0);

Checks if an unused forward declaration is in a wrong namespace.

The check inspects all unused forward declarations and checks if there is any declaration/definition with the same name existing, which could indicate that the forward declaration is in a potentially wrong namespace.

namespace na { struct A; }
namespace nb { struct A {}; }
nb::A a;
// warning : no definition found for 'A', but a definition with the same name
// 'A' found in another namespace 'nb::'

This check can only generate warnings, but it can't suggest a fix at this point.

The check looks for perfect forwarding constructors that can hide copy or move constructors. If a non const lvalue reference is passed to the constructor, the forwarding reference parameter will be a better match than the const reference parameter of the copy constructor, so the perfect forwarding constructor will be called, which can be confusing. For detailed description of this issue see: Scott Meyers, Effective Modern C++, Item 26.

Consider the following example:

class Person {
public:
  // C1: perfect forwarding ctor
  template<typename T>
  explicit Person(T&& n) {}

  // C2: perfect forwarding ctor with parameter default value
  template<typename T>
  explicit Person(T&& n, int x = 1) {}

  // C3: perfect forwarding ctor guarded with enable_if
  template<typename T, typename X = enable_if_t<is_special<T>, void>>
  explicit Person(T&& n) {}

  // C4: variadic perfect forwarding ctor guarded with enable_if
  template<typename... A,
    enable_if_t<is_constructible_v<tuple<string, int>, A&&...>, int> = 0>
  explicit Person(A&&... a) {}

  // C5: perfect forwarding ctor guarded with requires expression
  template<typename T>
  requires requires { is_special<T>; }
  explicit Person(T&& n) {}

  // C6: perfect forwarding ctor guarded with concept requirement
  template<Special T>
  explicit Person(T&& n) {}

  // (possibly compiler generated) copy ctor
  Person(const Person& rhs);
};

The check warns for constructors C1 and C2, because those can hide copy and move constructors. We suppress warnings if the copy and the move constructors are both disabled (deleted or private), because there is nothing the perfect forwarding constructor could hide in this case. We also suppress warnings for constructors like C3-C6 that are guarded with an enable_if or a concept, assuming the programmer was aware of the possible hiding.

For deciding whether a constructor is guarded with enable_if, we consider the types of the constructor parameters, the default values of template type parameters and the types of non-type template parameters with a default literal value. If any part of these types is std::enable_if or std::enable_if_t, we assume the constructor is guarded.

The check diagnoses instances where a result of a multiplication is implicitly widened, and suggests (with fix-it) to either silence the code by making widening explicit, or to perform the multiplication in a wider type, to avoid the widening afterwards.

This is mainly useful when operating on very large buffers. For example, consider:

void zeroinit(char* base, unsigned width, unsigned height) {
  for(unsigned row = 0; row != height; ++row) {
    for(unsigned col = 0; col != width; ++col) {
      char* ptr = base + row * width + col;
      *ptr = 0;
    }
  }
}

This is fine in general, but if width * height overflows, you end up wrapping back to the beginning of base instead of processing the entire requested buffer.

Indeed, this only matters for pretty large buffers (4GB+), but that can happen very easily for example in image processing, where for that to happen you "only" need a ~269MPix image.

UseCXXStaticCastsInCppSources

When suggesting fix-its for C++ code, should C++-style static_cast<>()'s be suggested, or C-style casts. Defaults to true.

UseCXXHeadersInCppSources

When suggesting to include the appropriate header in C++ code, should <cstddef> header be suggested, or <stddef.h>. Defaults to true.

IgnoreConstantIntExpr

If the multiplication operands are compile-time constants (like literals or are constexpr) and fit within the source expression type, do not emit a diagnostic or suggested fix.  Only considers expressions where the source expression is a signed integer type.  Defaults to false.

Examples:

long mul(int a, int b) {
  return a * b; // warning: performing an implicit widening conversion to type 'long' of a multiplication performed in type 'int'
}

char* ptr_add(char *base, int a, int b) {
  return base + a * b; // warning: result of multiplication in type 'int' is used as a pointer offset after an implicit widening conversion to type 'ssize_t'
}

char ptr_subscript(char *base, int a, int b) {
  return base[a * b]; // warning: result of multiplication in type 'int' is used as a pointer offset after an implicit widening conversion to type 'ssize_t'
}

Checks for inaccurate use of the erase() method.

Algorithms like remove() do not actually remove any element from the container but return an iterator to the first redundant element at the end of the container. These redundant elements must be removed using the erase() method. This check warns when not all of the elements will be removed due to using an inappropriate overload.

For example, the following code erases only one element:

std::vector<int> xs;
...
xs.erase(std::remove(xs.begin(), xs.end(), 10));

Call the two-argument overload of erase() to remove the subrange:

std::vector<int> xs;
...
xs.erase(std::remove(xs.begin(), xs.end(), 10), xs.end());

Detects when a variable is both incremented/decremented and referenced inside a complex condition and suggests moving them outside to avoid ambiguity in the variable's value.

When a variable is modified and also used in a complex condition, it can lead to unexpected behavior. The side-effect of changing the variable's value within the condition can make the code difficult to reason about. Additionally, the developer's intended timing for the modification of the variable may not be clear, leading to misunderstandings and errors. This can be particularly problematic when the condition involves logical operators like && and ||, where the order of evaluation can further complicate the situation.

Consider the following example:

int i = 0;
// ...
if (i++ < 5 && i > 0) {
  // do something
}

In this example, the result of the expression may not be what the developer intended. The original intention of the developer could be to increment i after the entire condition is evaluated, but in reality, i will be incremented before i > 0 is executed. This can lead to unexpected behavior and bugs in the code. To fix this issue, the developer should separate the increment operation from the condition and perform it separately. For example, they can increment i in a separate statement before or after the condition is evaluated. This ensures that the value of i is predictable and consistent throughout the code.

int i = 0;
// ...
i++;
if (i <= 5 && i > 0) {
  // do something
}

Another common issue occurs when multiple increments or decrements are performed on the same variable inside a complex condition. For example:

int i = 4;
// ...
if (i++ < 5 || --i > 2) {
  // do something
}

There is a potential issue with this code due to the order of evaluation in C++. The || operator used in the condition statement guarantees that if the first operand evaluates to true, the second operand will not be evaluated. This means that if i were initially 4, the first operand i < 5 would evaluate to true and the second operand i > 2 would not be evaluated. As a result, the decrement operation --i would not be executed and i would hold value 5, which may not be the intended behavior for the developer.

To avoid this potential issue, the both increment and decrement operation on i should be moved outside the condition statement.

Detects incorrect usages of std::enable_if that don't name the nested type type.

In C++11 introduced std::enable_if as a convenient way to leverage SFINAE. One form of using std::enable_if is to declare an unnamed template type parameter with a default type equal to typename std::enable_if<condition>::type. If the author forgets to name the nested type type, then the code will always consider the candidate template even if the condition is not met.

Below are some examples of code using std::enable_if correctly and incorrect examples that this check flags.

template <typename T, typename = typename std::enable_if<T::some_trait>::type>
void valid_usage() { ... }

template <typename T, typename = std::enable_if_t<T::some_trait>>
void valid_usage_with_trait_helpers() { ... }

// The below code is not a correct application of SFINAE. Even if
// T::some_trait is not true, the function will still be considered in the
// set of function candidates. It can either incorrectly select the function
// when it should not be a candidates, and/or lead to hard compile errors
// if the body of the template does not compile if the condition is not
// satisfied.
template <typename T, typename = std::enable_if<T::some_trait>>
void invalid_usage() { ... }

// The tool suggests the following replacement for 'invalid_usage':
template <typename T, typename = typename std::enable_if<T::some_trait>::type>
void fixed_invalid_usage() { ... }

C++14 introduced the trait helper std::enable_if_t which reduces the likelihood of this error. C++20 introduces constraints, which generally supersede the use of std::enable_if. See modernize-type-traits for another tool that will replace std::enable_if with std::enable_if_t, and see modernize-use-constraints for another tool that replaces std::enable_if with C++20 constraints. Consider these newer mechanisms where possible.

Checks the usage of patterns known to produce incorrect rounding. Programmers often use:

(int)(double_expression + 0.5)

to round the double expression to an integer. The problem with this:

1. It is unnecessarily slow.
2. It is incorrect. The number 0.499999975 (smallest representable float number below 0.5) rounds to 1.0. Even worse behavior for negative numbers where both -0.5f and -1.4f both round to 0.0.

Finds obvious infinite loops (loops where the condition variable is not changed at all).

Finding infinite loops is well-known to be impossible (halting problem). However, it is possible to detect some obvious infinite loops, for example, if the loop condition is not changed. This check detects such loops. A loop is considered infinite if it does not have any loop exit statement (break, continue, goto, return, throw or a call to a function called as [[noreturn]]) and all of the following conditions hold for every variable in the condition:

• It is a local variable.
• It has no reference or pointer aliases.
• It is not a structure or class member.

Furthermore, the condition must not contain a function call to consider the loop infinite since functions may return different values for different calls.

For example, the following loop is considered infinite i is not changed in the body:

int i = 0, j = 0;
while (i < 10) {
  ++j;
}

Finds cases where integer division in a floating point context is likely to cause unintended loss of precision.

No reports are made if divisions are part of the following expressions:

• operands of operators expecting integral or bool types,
• call expressions of integral or bool types, and
• explicit cast expressions to integral or bool types,

as these are interpreted as signs of deliberateness from the programmer.

Examples:

float floatFunc(float);
int intFunc(int);
double d;
int i = 42;

// Warn, floating-point values expected.
d = 32 * 8 / (2 + i);
d = 8 * floatFunc(1 + 7 / 2);
d = i / (1 << 4);

// OK, no integer division.
d = 32 * 8.0 / (2 + i);
d = 8 * floatFunc(1 + 7.0 / 2);
d = (double)i / (1 << 4);

// OK, there are signs of deliberateness.
d = 1 << (i / 2);
d = 9 + intFunc(6 * i / 32);
d = (int)(i / 32) - 8;

Checks for attempts to get the name of a function from within a lambda expression. The name of a lambda is always something like operator(), which is almost never what was intended.

Example:

void FancyFunction() {
  [] { printf("Called from %s\n", __func__); }();
  [] { printf("Now called from %s\n", __FUNCTION__); }();
}

Output:

Called from operator()
Now called from operator()

Likely intended output:

Called from FancyFunction
Now called from FancyFunction

IgnoreMacros

The value true specifies that attempting to get the name of a function from within a macro should not be diagnosed. The default value is false.

Finds macros that can have unexpected behavior due to missing parentheses.

Macros are expanded by the preprocessor as-is. As a result, there can be unexpected behavior; operators may be evaluated in unexpected order and unary operators may become binary operators, etc.

When the replacement list has an expression, it is recommended to surround it with parentheses. This ensures that the macro result is evaluated completely before it is used.

It is also recommended to surround macro arguments in the replacement list with parentheses. This ensures that the argument value is calculated properly.

This check corresponds to the CERT C Coding Standard rule PRE20-C. Macro replacement lists should be parenthesized.

Checks for repeated argument with side effects in macros.

Finds cases where 1 is added to the string in the argument to strlen(), strnlen(), strnlen_s(), wcslen(), wcsnlen(), and wcsnlen_s() instead of the result and the value is used as an argument to a memory allocation function (malloc(), calloc(), realloc(), alloca()) or the new[] operator in C++. The check detects error cases even if one of these functions (except the new[] operator) is called by a constant function pointer. Cases where 1 is added both to the parameter and the result of the strlen()-like function are ignored, as are cases where the whole addition is surrounded by extra parentheses.

C example code:

void bad_malloc(char *str) {
  char *c = (char*) malloc(strlen(str + 1));
}

The suggested fix is to add 1 to the return value of strlen() and not to its argument. In the example above the fix would be

char *c = (char*) malloc(strlen(str) + 1);

C++ example code:

void bad_new(char *str) {
  char *c = new char[strlen(str + 1)];
}

As in the C code with the malloc() function, the suggested fix is to add 1 to the return value of strlen() and not to its argument. In the example above the fix would be

char *c = new char[strlen(str) + 1];

Example for silencing the diagnostic:

void bad_malloc(char *str) {
  char *c = (char*) malloc(strlen((str + 1)));
}

Finds cases where an integer expression is added to or subtracted from the result of a memory allocation function (malloc(), calloc(), realloc(), alloca()) instead of its argument. The check detects error cases even if one of these functions is called by a constant function pointer.

Example code:

void bad_malloc(int n) {
  char *p = (char*) malloc(n) + 10;
}

The suggested fix is to add the integer expression to the argument of malloc and not to its result. In the example above the fix would be

char *p = (char*) malloc(n + 10);

This check will warn when there is a cast of a calculation result to a bigger type. If the intention of the cast is to avoid loss of precision then the cast is misplaced, and there can be loss of precision. Otherwise the cast is ineffective.

Example code:

long f(int x) {
    return (long)(x * 1000);
}

The result x * 1000 is first calculated using int precision. If the result exceeds int precision there is loss of precision. Then the result is casted to long.

If there is no loss of precision then the cast can be removed or you can explicitly cast to int instead.

If you want to avoid loss of precision then put the cast in a proper location, for instance:

long f(int x) {
    return (long)x * 1000;
}

Forgetting to place the cast at all is at least as dangerous and at least as common as misplacing it. If CheckImplicitCasts is enabled the check also detects these cases, for instance:

long f(int x) {
    return x * 1000;
}

Currently warnings are only written for integer conversion. No warning is written for this code:

double f(float x) {
    return (double)(x * 10.0f);
}

CheckImplicitCasts

If true, enables detection of implicit casts. Default is false.

Warns if std::move is called on a forwarding reference, for example:

template <typename T>
void foo(T&& t) {
  bar(std::move(t));
}

Forwarding references should typically be passed to std::forward instead of std::move, and this is the fix that will be suggested.

(A forwarding reference is an rvalue reference of a type that is a deduced function template argument.)

In this example, the suggested fix would be

bar(std::forward<T>(t));

Code like the example above is sometimes written with the expectation that T&& will always end up being an rvalue reference, no matter what type is deduced for T, and that it is therefore not possible to pass an lvalue to foo(). However, this is not true. Consider this example:

std::string s = "Hello, world";
foo(s);

This code compiles and, after the call to foo(), s is left in an indeterminate state because it has been moved from. This may be surprising to the caller of foo() because no std::move was used when calling foo().

The reason for this behavior lies in the special rule for template argument deduction on function templates like foo() -- i.e. on function templates that take an rvalue reference argument of a type that is a deduced function template argument. (See section [temp.deduct.call]/3 in the C++11 standard.)

If foo() is called on an lvalue (as in the example above), then T is deduced to be an lvalue reference. In the example, T is deduced to be std::string &. The type of the argument t therefore becomes std::string& &&; by the reference collapsing rules, this collapses to std::string&.

This means that the foo(s) call passes s as an lvalue reference, and foo() ends up moving s and thereby placing it into an indeterminate state.

Detects implicit conversions between pointers of different levels of indirection.

Conversions between pointer types of different levels of indirection can be dangerous and may lead to undefined behavior, particularly if the converted pointer is later cast to a type with a different level of indirection. For example, converting a pointer to a pointer to an int (int**) to a void* can result in the loss of information about the original level of indirection, which can cause problems when attempting to use the converted pointer. If the converted pointer is later cast to a type with a different level of indirection and dereferenced, it may lead to access violations, memory corruption, or other undefined behavior.

Consider the following example:

void foo(void* ptr);

int main() {
  int x = 42;
  int* ptr = &x;
  int** ptr_ptr = &ptr;
  foo(ptr_ptr); // warning will trigger here
  return 0;
}

In this example, foo() is called with ptr_ptr as its argument. However, ptr_ptr is a int** pointer, while foo() expects a void* pointer. This results in an implicit pointer level conversion, which could cause issues if foo() dereferences the pointer assuming it's a int* pointer.

Using an explicit cast is a recommended solution to prevent issues caused by implicit pointer level conversion, as it allows the developer to explicitly state their intention and show their reasoning for the type conversion. Additionally, it is recommended that developers thoroughly check and verify the safety of the conversion before using an explicit cast. This extra level of caution can help catch potential issues early on in the development process, improving the overall reliability and maintainability of the code.

Finds multiple new operator calls in a single expression, where the allocated memory by the first new may leak if the second allocation fails and throws exception.

C++ does often not specify the exact order of evaluation of the operands of an operator or arguments of a function. Therefore if a first allocation succeeds and a second fails, in an exception handler it is not possible to tell which allocation has failed and free the memory. Even if the order is fixed the result of a first new may be stored in a temporary location that is not reachable at the time when a second allocation fails. It is best to avoid any expression that contains more than one operator new call, if exception handling is used to check for allocation errors.

Different rules apply for are the short-circuit operators || and && and the , operator, where evaluation of one side must be completed before the other starts. Expressions of a list-initialization (initialization or construction using { and } characters) are evaluated in fixed order. Similarly, condition of a ? operator is evaluated before the branches are evaluated.

The check reports warning if two new calls appear in one expression at different sides of an operator, or if new calls appear in different arguments of a function call (that can be an object construction with () syntax). These new calls can be nested at any level. For any warning to be emitted the new calls should be in a code block where exception handling is used with catch for std::bad_alloc or std::exception. At ||, &&, ,, ? (condition and one branch) operators no warning is emitted. No warning is emitted if both of the memory allocations are not assigned to a variable or not passed directly to a function. The reason is that in this case the memory may be intentionally not freed or the allocated objects can be self-destructing objects.

Examples:

struct A {
  int Var;
};
struct B {
  B();
  B(A *);
  int Var;
};
struct C {
  int *X1;
  int *X2;
};

void f(A *, B *);
int f1(A *);
int f1(B *);
bool f2(A *);

void foo() {
  A *PtrA;
  B *PtrB;
  try {
    // Allocation of 'B'/'A' may fail after memory for 'A'/'B' was allocated.
    f(new A, new B); // warning: memory allocation may leak if an other allocation is sequenced after it and throws an exception; order of these allocations is undefined

    // List (aggregate) initialization is used.
    C C1{new int, new int}; // no warning

    // Allocation of 'B'/'A' may fail after memory for 'A'/'B' was allocated but not yet passed to function 'f1'.
    int X = f1(new A) + f1(new B); // warning: memory allocation may leak if an other allocation is sequenced after it and throws an exception; order of these allocations is undefined

    // Allocation of 'B' may fail after memory for 'A' was allocated.
    // From C++17 on memory for 'B' is allocated first but still may leak if allocation of 'A' fails.
    PtrB = new B(new A); // warning: memory allocation may leak if an other allocation is sequenced after it and throws an exception

    // 'new A' and 'new B' may be performed in any order.
    // 'new B'/'new A' may fail after memory for 'A'/'B' was allocated but not assigned to 'PtrA'/'PtrB'.
    (PtrA = new A)->Var = (PtrB = new B)->Var; // warning: memory allocation may leak if an other allocation is sequenced after it and throws an exception; order of these allocations is undefined

    // Evaluation of 'f2(new A)' must be finished before 'f1(new B)' starts.
    // If 'new B' fails the allocated memory for 'A' is supposedly handled correctly because function 'f2' could take the ownership.
    bool Z = f2(new A) || f1(new B); // no warning

    X = (f2(new A) ? f1(new A) : f1(new B)); // no warning

    // No warning if the result of both allocations is not passed to a function
    // or stored in a variable.
    (new A)->Var = (new B)->Var; // no warning

    // No warning if at least one non-throwing allocation is used.
    f(new(std::nothrow) A, new B); // no warning
  } catch(std::bad_alloc) {
  }

  // No warning if the allocation is outside a try block (or no catch handler exists for std::bad_alloc).
  // (The fact if exceptions can escape from 'foo' is not taken into account.)
  f(new A, new B); // no warning
}

Detect multiple statement macros that are used in unbraced conditionals. Only the first statement of the macro will be inside the conditional and the other ones will be executed unconditionally.

Example:

#define INCREMENT_TWO(x, y) (x)++; (y)++
if (do_increment)
  INCREMENT_TWO(a, b);  // (b)++ will be executed unconditionally.

The bugprone-narrowing-conversions check is an alias, please see cppcoreguidelines-narrowing-conversions for more information.

Finds pointers with the noescape attribute that are captured by an asynchronously-executed block. The block arguments in dispatch_async() and dispatch_after() are guaranteed to escape, so it is an error if a pointer with the noescape attribute is captured by one of these blocks.

The following is an example of an invalid use of the noescape attribute.

void foo(__attribute__((noescape)) int *p) {
  dispatch_async(queue, ^{
    *p = 123;
  });
});

Detect implicit and explicit casts of enum type into bool where enum type doesn't have a zero-value enumerator. If the enum is used only to hold values equal to its enumerators, then conversion to bool will always result in true value. This can lead to unnecessary code that reduces readability and maintainability and can result in bugs.

May produce false positives if the enum is used to store other values (used as a bit-mask or zero-initialized on purpose). To deal with them, // NOLINT or casting first to the underlying type before casting to bool can be used.

It is important to note that this check will not generate warnings if the definition of the enumeration type is not available. Additionally, C++11 enumeration classes are supported by this check.

Overall, this check serves to improve code quality and readability by identifying and flagging instances where implicit or explicit casts from enumeration types to boolean could cause potential issues.

enum EStatus {
  OK = 1,
  NOT_OK,
  UNKNOWN
};

void process(EStatus status) {
  if (!status) {
    // this true-branch won't be executed
    return;
  }
  // proceed with "valid data"
}

EnumIgnoreList

Option is used to ignore certain enum types when checking for implicit/explicit casts to bool. It accepts a semicolon-separated list of (fully qualified) enum type names or regular expressions that match the enum type names. The default value is an empty string, which means no enums will be ignored.

Finds function calls where it is possible to cause a not null-terminated result. Usually the proper length of a string is strlen(src) + 1 or equal length of this expression, because the null terminator needs an extra space. Without the null terminator it can result in undefined behavior when the string is read.

The following and their respective wchar_t based functions are checked:

memcpy, memcpy_s, memchr, memmove, memmove_s, strerror_s, strncmp, strxfrm

The following is a real-world example where the programmer forgot to increase the passed third argument, which is size_t length. That is why the length of the allocated memory is not enough to hold the null terminator.

static char *stringCpy(const std::string &str) {
  char *result = reinterpret_cast<char *>(malloc(str.size()));
  memcpy(result, str.data(), str.size());
  return result;
}

In addition to issuing warnings, fix-it rewrites all the necessary code. It also tries to adjust the capacity of the destination array:

static char *stringCpy(const std::string &str) {
  char *result = reinterpret_cast<char *>(malloc(str.size() + 1));
  strcpy(result, str.data());
  return result;
}

Note: It cannot guarantee to rewrite every of the path-sensitive memory allocations.

It is possible to rewrite the memcpy() and memcpy_s() calls as the following four functions:  strcpy(), strncpy(), strcpy_s(), strncpy_s(), where the latter two are the safer versions of the former two. It rewrites the wchar_t based memory handler functions respectively.

• If copy to the destination array cannot overflow [1] the new function should be the older copy function (ending with cpy), because it is more efficient than the safe version.
• If copy to the destination array can overflow [1] and WantToUseSafeFunctions is set to true and it is possible to obtain the capacity of the destination array then the new function could be the safe version (ending with cpy_s).
• If the new function is could be safe version and C++ files are analyzed and the destination array is plain char/wchar_t without un/signed then the length of the destination array can be omitted.
• If the new function is could be safe version and the destination array is un/signed it needs to be casted to plain char */wchar_t *.

[1] It is possible to overflow:

• If the capacity of the destination array is unknown.
• If the given length is equal to the destination array's capacity.

• If the given length is strlen(source) or equal length of this expression then the new function should be the older copy function (ending with cpy), as it is more efficient than the safe version (ending with cpy_s).
• Otherwise we assume that the programmer wanted to copy 'N' characters, so the new function is ncpy-like which copies 'N' characters.

It transforms the wchar_t based memory and string handler functions respectively (where only strerror_s does not have wchar_t based alias).

memcpy Please visit the Transformation rules of 'memcpy()' section.

memchr Usually there is a C-style cast and it is needed to be removed, because the new function strchr's return type is correct. The given length is going to be removed.

memmove If safe functions are available the new function is memmove_s, which has a new second argument which is the length of the destination array, it is adjusted, and the length of the source string is incremented by one. If safe functions are not available the given length is incremented by one.

memmove_s The given length is incremented by one.

strerror_s The given length is incremented by one.

strncmp If the third argument is the first or the second argument's length + 1 it has to be truncated without the + 1 operation.

strxfrm The given length is incremented by one.

WantToUseSafeFunctions

The value true specifies that the target environment is considered to implement '_s' suffixed memory and string handler functions which are safer than older versions (e.g. 'memcpy_s()'). The default value is true.

Detects potentially unintentional and redundant conversions where a value is extracted from an optional-like type and then used to create a new instance of the same optional-like type.

These conversions might be the result of developer oversight, leftovers from code refactoring, or other situations that could lead to unintended exceptions or cases where the resulting optional is always initialized, which might be unexpected behavior.

To illustrate, consider the following problematic code snippet:

#include <optional>

void print(std::optional<int>);

int main()
{
  std::optional<int> opt;
  // ...

  // Unintentional conversion from std::optional<int> to int and back to
  // std::optional<int>:
  print(opt.value());

  // ...
}

A better approach would be to directly pass opt to the print function without extracting its value:

#include <optional>

void print(std::optional<int>);

int main()
{
  std::optional<int> opt;
  // ...

  // Proposed code: Directly pass the std::optional<int> to the print
  // function.
  print(opt);

  // ...
}

By passing opt directly to the print function, unnecessary conversions are avoided, and potential unintended behavior or exceptions are minimized.

Value extraction using operator * is matched by default. The support for non-standard optional types such as boost::optional or absl::optional may be limited.

OptionalTypes

Semicolon-separated list of (fully qualified) optional type names or regular expressions that match the optional types. Default value is ::std::optional;::absl::optional;::boost::optional.

ValueMethods

Semicolon-separated list of (fully qualified) method names or regular expressions that match the methods. Default value is ::value$;::get$.

Detects and fixes calls to grand-...parent virtual methods instead of calls to overridden parent's virtual methods.

struct A {
  int virtual foo() {...}
};

struct B: public A {
  int foo() override {...}
};

struct C: public B {
  int foo() override { A::foo(); }
//                     ^^^^^^^^
// warning: qualified name A::foo refers to a member overridden in subclass; did you mean 'B'?  [bugprone-parent-virtual-call]
};

Finds pointer arithmetic performed on classes that contain a virtual function.

Pointer arithmetic on polymorphic objects where the pointer's static type is different from its dynamic type is undefined behavior, as the two types could have different sizes, and thus the vtable pointer could point to an invalid address.

Finding pointers where the static type contains a virtual member function is a good heuristic, as the pointer is likely to point to a different, derived object.

Example:

struct Base {
  virtual void ~Base();
};

struct Derived : public Base {};

void foo() {
  Base *b = new Derived[10];

  b += 1;
  // warning: pointer arithmetic on class that declares a virtual function can
  // result in undefined behavior if the dynamic type differs from the
  // pointer type

  delete[] static_cast<Derived*>(b);
}

IgnoreInheritedVirtualFunctions

When true, objects that only inherit a virtual function are not checked. Classes that do not declare a new virtual function are excluded by default, as they make up the majority of false positives. Default: false.

void bar() {
  Base *b = new Base[10];
  b += 1; // warning, as Base declares a virtual destructor

  delete[] b;

  Derived *d = new Derived[10]; // Derived overrides the destructor, and
                                // declares no other virtual functions
  d += 1; // warning only if IgnoreVirtualDeclarationsOnly is set to false

  delete[] d;
}

This check corresponds to the SEI Cert rule CTR56-CPP. Do not use pointer arithmetic on polymorphic objects.

Checks if any calls to pthread_* or posix_* functions (except posix_openpt) expect negative return values. These functions return either 0 on success or an errno on failure, which is positive only.

Example buggy usage looks like:

if (posix_fadvise(...) < 0) {

This will never happen as the return value is always non-negative. A simple fix could be:

if (posix_fadvise(...) > 0) {

Finds condition variables in nested if statements that were also checked in the outer if statement and were not changed.

Simple example:

bool onFire = isBurning();
if (onFire) {
  if (onFire)
    scream();
}

Here onFire is checked both in the outer if and the inner if statement without a possible change between the two checks. The check warns for this code and suggests removal of the second checking of variable onFire.

The checker also detects redundant condition checks if the condition variable is an operand of a logical "and" (&&) or a logical "or" (||) operator:

bool onFire = isBurning();
if (onFire) {
  if (onFire && peopleInTheBuilding > 0)
    scream();
}

bool onFire = isBurning();
if (onFire) {
  if (onFire || isCollapsing())
    scream();
}

In the first case (logical "and") the suggested fix is to remove the redundant condition variable and keep the other side of the &&. In the second case (logical "or") the whole if is removed similarly to the simple case on the top.

The condition of the outer if statement may also be a logical "and" (&&) expression:

bool onFire = isBurning();
if (onFire && fireFighters < 10) {
  if (someOtherCondition()) {
    if (onFire)
      scream();
  }
}

The error is also detected if both the outer statement is a logical "and" (&&) and the inner statement is a logical "and" (&&) or "or" (||). The inner if statement does not have to be a direct descendant of the outer one.

No error is detected if the condition variable may have been changed between the two checks:

bool onFire = isBurning();
if (onFire) {
  tryToExtinguish(onFire);
  if (onFire && peopleInTheBuilding > 0)
    scream();
}

Every possible change is considered, thus if the condition variable is not a local variable of the function, it is a volatile or it has an alias (pointer or reference) then no warning is issued.

The else branch is not checked currently for negated condition variable:

bool onFire = isBurning();
if (onFire) {
  scream();
} else {
  if (!onFire) {
    continueWork();
  }
}

The checker currently only detects redundant checking of single condition variables. More complex expressions are not checked:

if (peopleInTheBuilding == 1) {
  if (peopleInTheBuilding == 1) {
    doSomething();
  }
}

cert-dcl37-c and cert-dcl51-cpp redirect here as an alias for this check.

Checks for usages of identifiers reserved for use by the implementation.

The C and C++ standards both reserve the following names for such use:

• identifiers that begin with an underscore followed by an uppercase letter;
• identifiers in the global namespace that begin with an underscore.

The C standard additionally reserves names beginning with a double underscore, while the C++ standard strengthens this to reserve names with a double underscore occurring anywhere.

Violating the naming rules above results in undefined behavior.

namespace NS {
  void __f(); // name is not allowed in user code
  using _Int = int; // same with this
  #define cool__macro // also this
}
int _g(); // disallowed in global namespace only

The check can also be inverted, i.e. it can be configured to flag any identifier that is _not_ a reserved identifier. This mode is for use by e.g. standard library implementors, to ensure they don't infringe on the user namespace.

This check does not (yet) check for other reserved names, e.g. macro names identical to language keywords, and names specifically reserved by language standards, e.g. C++ 'zombie names' and C future library directions.

This check corresponds to CERT C Coding Standard rule DCL37-C. Do not declare or define a reserved identifier as well as its C++ counterpart, DCL51-CPP. Do not declare or define a reserved identifier.

Invert

If true, inverts the check, i.e. flags names that are not reserved. Default is false.

AllowedIdentifiers

Semicolon-separated list of regular expressions that the check ignores. Default is an empty list.

Detects return statements that return a constant reference parameter as constant reference. This may cause use-after-free errors if the caller uses xvalues as arguments.

In C++, constant reference parameters can accept xvalues which will be destructed after the call. When the function returns such a parameter also as constant reference, then the returned reference can be used after the object it refers to has been destroyed.

struct S {
  int v;
  S(int);
  ~S();
};

const S &fn(const S &a) {
  return a;
}

const S& s = fn(S{1});
s.v; // use after free

Finds initializations of C++ shared pointers to non-array type that are initialized with an array.

If a shared pointer std::shared_ptr<T> is initialized with a new-expression new T[] the memory is not deallocated correctly. The pointer uses plain delete in this case to deallocate the target memory. Instead a delete[] call is needed. A std::shared_ptr<T[]> calls the correct delete operator.

The check offers replacement of shared_ptr<T> to shared_ptr<T[]> if it is used at a single variable declaration (one variable in one statement).

Example:

std::shared_ptr<Foo> x(new Foo[10]); // -> std::shared_ptr<Foo[]> x(new Foo[10]);
//                     ^ warning: shared pointer to non-array is initialized with array [bugprone-shared-ptr-array-mismatch]
std::shared_ptr<Foo> x1(new Foo), x2(new Foo[10]); // no replacement
//                                   ^ warning: shared pointer to non-array is initialized with array [bugprone-shared-ptr-array-mismatch]

std::shared_ptr<Foo> x3(new Foo[10], [](const Foo *ptr) { delete[] ptr; }); // no warning

struct S {
  std::shared_ptr<Foo> x(new Foo[10]); // no replacement in this case
  //                     ^ warning: shared pointer to non-array is initialized with array [bugprone-shared-ptr-array-mismatch]
};

This check partially covers the CERT C++ Coding Standard rule MEM51-CPP. Properly deallocate dynamically allocated resources However, only the std::shared_ptr case is detected by this check.

Finds specific constructs in signal handler functions that can cause undefined behavior. The rules for what is allowed differ between C++ language versions.

Checked signal handler rules for C:

• Calls to non-asynchronous-safe functions are not allowed.

Checked signal handler rules for up to and including C++14:

• Calls to non-asynchronous-safe functions are not allowed.
• C++-specific code constructs are not allowed in signal handlers. In other words, only the common subset of C and C++ is allowed to be used.
• Calls to functions with non-C linkage are not allowed (including the signal handler itself).

The check is disabled on C++17 and later.

Asynchronous-safety is determined by comparing the function's name against a set of known functions. In addition, the function must come from a system header include and in a global namespace. The (possible) arguments passed to the function are not checked. Any function that cannot be determined to be asynchronous-safe is assumed to be non-asynchronous-safe by the check, including user functions for which only the declaration is visible. Calls to user-defined functions with visible definitions are checked recursively.

This check implements the CERT C Coding Standard rule SIG30-C. Call only asynchronous-safe functions within signal handlers and the rule MSC54-CPP. A signal handler must be a plain old function. It has the alias names cert-sig30-c and cert-msc54-cpp.

AsyncSafeFunctionSet

Selects which set of functions is considered as asynchronous-safe (and therefore allowed in signal handlers). It can be set to the following values:

minimal

Selects a minimal set that is defined in the CERT SIG30-C rule. and includes functions abort(), _Exit(), quick_exit() and signal().

POSIX

Selects a larger set of functions that is listed in POSIX.1-2017 (see this link for more information). The following functions are included: _Exit, _exit, abort, accept, access, aio_error, aio_return, aio_suspend, alarm, bind, cfgetispeed, cfgetospeed, cfsetispeed, cfsetospeed, chdir, chmod, chown, clock_gettime, close, connect, creat, dup, dup2, execl, execle, execv, execve, faccessat, fchdir, fchmod, fchmodat, fchown, fchownat, fcntl, fdatasync, fexecve, ffs, fork, fstat, fstatat, fsync, ftruncate, futimens, getegid, geteuid, getgid, getgroups, getpeername, getpgrp, getpid, getppid, getsockname, getsockopt, getuid, htonl, htons, kill, link, linkat, listen, longjmp, lseek, lstat, memccpy, memchr, memcmp, memcpy, memmove, memset, mkdir, mkdirat, mkfifo, mkfifoat, mknod, mknodat, ntohl, ntohs, open, openat, pause, pipe, poll, posix_trace_event, pselect, pthread_kill, pthread_self, pthread_sigmask, quick_exit, raise, read, readlink, readlinkat, recv, recvfrom, recvmsg, rename, renameat, rmdir, select, sem_post, send, sendmsg, sendto, setgid, setpgid, setsid, setsockopt, setuid, shutdown, sigaction, sigaddset, sigdelset, sigemptyset, sigfillset, sigismember, siglongjmp, signal, sigpause, sigpending, sigprocmask, sigqueue, sigset, sigsuspend, sleep, sockatmark, socket, socketpair, stat, stpcpy, stpncpy, strcat, strchr, strcmp, strcpy, strcspn, strlen, strncat, strncmp, strncpy, strnlen, strpbrk, strrchr, strspn, strstr, strtok_r, symlink, symlinkat, tcdrain, tcflow, tcflush, tcgetattr, tcgetpgrp, tcsendbreak, tcsetattr, tcsetpgrp, time, timer_getoverrun, timer_gettime, timer_settime, times, umask, uname, unlink, unlinkat, utime, utimensat, utimes, wait, waitpid, wcpcpy, wcpncpy, wcscat, wcschr, wcscmp, wcscpy, wcscspn, wcslen, wcsncat, wcsncmp, wcsncpy, wcsnlen, wcspbrk, wcsrchr, wcsspn, wcsstr, wcstok, wmemchr, wmemcmp, wmemcpy, wmemmove, wmemset, write

The function quick_exit is not included in the POSIX list but it is included here in the set of safe functions.

The default value is POSIX.

cert-str34-c redirects here as an alias for this check. For the CERT alias, the DiagnoseSignedUnsignedCharComparisons option is set to false.

Finds those signed char -> integer conversions which might indicate a programming error. The basic problem with the signed char, that it might store the non-ASCII characters as negative values. This behavior can cause a misunderstanding of the written code both when an explicit and when an implicit conversion happens.

When the code contains an explicit signed char -> integer conversion, the human programmer probably expects that the converted value matches with the character code (a value from [0..255]), however, the actual value is in [-128..127] interval. To avoid this kind of misinterpretation, the desired way of converting from a signed char to an integer value is converting to unsigned char first, which stores all the characters in the positive [0..255] interval which matches the known character codes.

In case of implicit conversion, the programmer might not actually be aware that a conversion happened and char value is used as an integer. There are some use cases when this unawareness might lead to a functionally imperfect code. For example, checking the equality of a signed char and an unsigned char variable is something we should avoid in C++ code. During this comparison, the two variables are converted to integers which have different value ranges. For signed char, the non-ASCII characters are stored as a value in [-128..-1] interval, while the same characters are stored in the [128..255] interval for an unsigned char.

It depends on the actual platform whether plain char is handled as signed char by default and so it is caught by this check or not. To change the default behavior you can use -funsigned-char and -fsigned-char compilation options.

Currently, this check warns in the following cases: - signed char is assigned to an integer variable - signed char and unsigned char are compared with equality/inequality operator - signed char is converted to an integer in the array subscript

See also: STR34-C. Cast characters to unsigned char before converting to larger integer sizes

A good example from the CERT description when a char variable is used to read from a file that might contain non-ASCII characters. The problem comes up when the code uses the -1 integer value as EOF, while the 255 character code is also stored as -1 in two's complement form of char type. See a simple example of this below. This code stops not only when it reaches the end of the file, but also when it gets a character with the 255 code.

#define EOF (-1)

int read(void) {
  char CChar;
  int IChar = EOF;

  if (readChar(CChar)) {
    IChar = CChar;
  }
  return IChar;
}

A proper way to fix the code above is converting the char variable to an unsigned char value first.

#define EOF (-1)

int read(void) {
  char CChar;
  int IChar = EOF;

  if (readChar(CChar)) {
    IChar = static_cast<unsigned char>(CChar);
  }
  return IChar;
}

Another use case is checking the equality of two char variables with different signedness. Inside the non-ASCII value range this comparison between a signed char and an unsigned char always returns false.

bool compare(signed char SChar, unsigned char USChar) {
  if (SChar == USChar)
    return true;
  return false;
}

The easiest way to fix this kind of comparison is casting one of the arguments, so both arguments will have the same type.

bool compare(signed char SChar, unsigned char USChar) {
  if (static_cast<unsigned char>(SChar) == USChar)
    return true;
  return false;
}

CharTypdefsToIgnore

A semicolon-separated list of typedef names. In this list, we can list typedefs for char or signed char, which will be ignored by the check. This is useful when a typedef introduces an integer alias like sal_Int8 or int8_t. In this case, human misinterpretation is not an issue.

DiagnoseSignedUnsignedCharComparisons

When true, the check will warn on signed char/unsigned char comparisons, otherwise these comparisons are ignored. By default, this option is set to true.

The check finds usages of sizeof on expressions of STL container types. Most likely the user wanted to use .size() instead.

All class/struct types declared in namespace std:: having a const size() method are considered containers, with the exception of std::bitset and std::array.

Examples:

std::string s;
int a = 47 + sizeof(s); // warning: sizeof() doesn't return the size of the container. Did you mean .size()?

int b = sizeof(std::string); // no warning, probably intended.

std::string array_of_strings[10];
int c = sizeof(array_of_strings) / sizeof(array_of_strings[0]); // no warning, definitely intended.

std::array<int, 3> std_array;
int d = sizeof(std_array); // no warning, probably intended.

The check finds usages of sizeof expressions which are most likely errors.

The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. Misuse of this operator may be leading to errors and possible software vulnerabilities.

A common mistake is to query the sizeof of an integer literal. This is equivalent to query the size of its type (probably int). The intent of the programmer was probably to simply get the integer and not its size.

#define BUFLEN 42
char buf[BUFLEN];
memset(buf, 0, sizeof(BUFLEN));  // sizeof(42) ==> sizeof(int)

In cases, where there is an enum or integer to represent a type, a common mistake is to query the sizeof on the integer or enum that represents the type that should be used by sizeof. This results in the size of the integer and not of the type the integer represents:

enum data_type {
  FLOAT_TYPE,
  DOUBLE_TYPE
};

struct data {
  data_type type;
  void* buffer;
  data_type get_type() {
    return type;
  }
};

void f(data d, int numElements) {
  // should be sizeof(float) or sizeof(double), depending on d.get_type()
  int numBytes = numElements * sizeof(d.get_type());
  ...
}

The this keyword is evaluated to a pointer to an object of a given type. The expression sizeof(this) is returning the size of a pointer. The programmer most likely wanted the size of the object and not the size of the pointer.

class Point {
  [...]
  size_t size() { return sizeof(this); }  // should probably be sizeof(*this)
  [...]
};

There is a subtle difference between declaring a string literal with char* A = "" and char A[] = "". The first case has the type char* instead of the aggregate type char[]. Using sizeof on an object declared with char* type is returning the size of a pointer instead of the number of characters (bytes) in the string literal.

const char* kMessage = "Hello World!";      // const char kMessage[] = "...";
void getMessage(char* buf) {
  memcpy(buf, kMessage, sizeof(kMessage));  // sizeof(char*)
}

A common mistake is to compute the size of a pointer instead of its pointee. These cases may occur because of explicit cast or implicit conversion.

int A[10];
memset(A, 0, sizeof(A + 0));

struct Point point;
memset(point, 0, sizeof(&point));

Dividing sizeof expressions is typically used to retrieve the number of elements of an aggregate. This check warns on incompatible or suspicious cases.

In the following example, the entity has 10-bytes and is incompatible with the type int which has 4 bytes.

char buf[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };  // sizeof(buf) => 10
void getMessage(char* dst) {
  memcpy(dst, buf, sizeof(buf) / sizeof(int));  // sizeof(int) => 4  [incompatible sizes]
}

In the following example, the expression sizeof(Values) is returning the size of char*. One can easily be fooled by its declaration, but in parameter declaration the size '10' is ignored and the function is receiving a char*.

char OrderedValues[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
return CompareArray(char Values[10]) {
  return memcmp(OrderedValues, Values, sizeof(Values)) == 0;  // sizeof(Values) ==> sizeof(char*) [implicit cast to char*]
}

Multiplying sizeof expressions typically makes no sense and is probably a logic error. In the following example, the programmer used * instead of /.

const char kMessage[] = "Hello World!";
void getMessage(char* buf) {
  memcpy(buf, kMessage, sizeof(kMessage) * sizeof(char));  //  sizeof(kMessage) / sizeof(char)
}

This check may trigger on code using the arraysize macro. The following code is working correctly but should be simplified by using only the sizeof operator.

extern Object objects[100];
void InitializeObjects() {
  memset(objects, 0, arraysize(objects) * sizeof(Object));  // sizeof(objects)
}

Getting the sizeof of a sizeof makes no sense and is typically an error hidden through macros.

#define INT_SZ sizeof(int)
int buf[] = { 42 };
void getInt(int* dst) {
  memcpy(dst, buf, sizeof(INT_SZ));  // sizeof(sizeof(int)) is suspicious.
}

WarnOnSizeOfConstant

When true, the check will warn on an expression like sizeof(CONSTANT). Default is true.

WarnOnSizeOfIntegerExpression

When true, the check will warn on an expression like sizeof(expr) where the expression results in an integer. Default is false.

WarnOnSizeOfThis

When true, the check will warn on an expression like sizeof(this). Default is true.

WarnOnSizeOfCompareToConstant

When true, the check will warn on an expression like sizeof(expr) <= k for a suspicious constant k while k is 0 or greater than 0x8000. Default is true.

WarnOnSizeOfPointerToAggregate

When true, the check will warn when the argument of sizeof is either a pointer-to-aggregate type, an expression returning a pointer-to-aggregate value or an expression that returns a pointer from an array-to-pointer conversion (that may be implicit or explicit, for example array + 2 or (int *)array). Default is true.

WarnOnSizeOfPointer

When true, the check will report all expressions where the argument of sizeof is an expression that produces a pointer (except for a few idiomatic expressions that are probably intentional and correct). This detects occurrences of CWE 467. Default is false.

Finds cnd_wait, cnd_timedwait, wait, wait_for, or wait_until function calls when the function is not invoked from a loop that checks whether a condition predicate holds or the function has a condition parameter.

if (condition_predicate) {
    condition.wait(lk);
}

if (condition_predicate) {
    if (thrd_success != cnd_wait(&condition, &lock)) {
    }
}

This check corresponds to the CERT C++ Coding Standard rule CON54-CPP. Wrap functions that can spuriously wake up in a loop. and CERT C Coding Standard rule CON36-C. Wrap functions that can spuriously wake up in a loop.

Warns when empty() is used on a range and the result is ignored. Suggests clear() if it is an existing member function.

The empty() method on several common ranges returns a Boolean indicating whether or not the range is empty, but is often mistakenly interpreted as a way to clear the contents of a range. Some ranges offer a clear() method for this purpose. This check warns when a call to empty returns a result that is ignored, and suggests replacing it with a call to clear() if it is available as a member function of the range.

For example, the following code could be used to indicate whether a range is empty or not, but the result is ignored:

std::vector<int> v;
...
v.empty();

A call to clear() would appropriately clear the contents of the range:

std::vector<int> v;
...
v.clear();

Limitations:

• Doesn't warn if empty() is defined and used with the ignore result in the class template definition (for example in the library implementation). These error cases can be caught with [[nodiscard]] attribute.

Finds string constructors that are suspicious and probably errors.

A common mistake is to swap parameters to the 'fill' string-constructor.

Examples:

std::string str('x', 50); // should be str(50, 'x')

Calling the string-literal constructor with a length bigger than the literal is suspicious and adds extra random characters to the string.

Examples:

std::string("test", 200);   // Will include random characters after "test".
std::string_view("test", 200);

Creating an empty string from constructors with parameters is considered suspicious. The programmer should use the empty constructor instead.

Examples:

std::string("test", 0);   // Creation of an empty string.
std::string_view("test", 0);

WarnOnLargeLength

When true, the check will warn on a string with a length greater than LargeLengthThreshold. Default is true.

LargeLengthThreshold

An integer specifying the large length threshold. Default is 0x800000.

StringNames

Default is ::std::basic_string;::std::basic_string_view.

Semicolon-delimited list of class names to apply this check to. By default ::std::basic_string applies to std::string and std::wstring. Set to e.g. ::std::basic_string;llvm::StringRef;QString to perform this check on custom classes.

The check finds assignments of an integer to std::basic_string<CharT> (std::string, std::wstring, etc.). The source of the problem is the following assignment operator of std::basic_string<CharT>:

basic_string& operator=( CharT ch );

Numeric types can be implicitly casted to character types.

std::string s;
int x = 5965;
s = 6;
s = x;

Use the appropriate conversion functions or character literals.

std::string s;
int x = 5965;
s = '6';
s = std::to_string(x);

In order to suppress false positives, use an explicit cast.

std::string s;
s = static_cast<char>(6);

Finds occurrences of string literal with embedded NUL character and validates their usage.

Special characters can be escaped within a string literal by using their hexadecimal encoding like \x42. A common mistake is to escape them like this \0x42 where the \0 stands for the NUL character.

const char* Example[] = "Invalid character: \0x12 should be \x12";
const char* Bytes[] = "\x03\0x02\0x01\0x00\0xFF\0xFF\0xFF";

String-like classes can manipulate strings with embedded NUL as they are keeping track of the bytes and the length. This is not the case for a char* (NUL-terminated) string.

A common mistake is to pass a string-literal with embedded NUL to a string constructor expecting a NUL-terminated string. The bytes after the first NUL character are truncated.

std::string str("abc\0def");  // "def" is truncated
str += "\0";                  // This statement is doing nothing
if (str == "\0abc") return;   // This expression is always true

Checks for various ways that the const CharT* constructor of std::basic_string_view can be passed a null argument and replaces them with the default constructor in most cases. For the comparison operators, braced initializer list does not compile so instead a call to .empty() or the empty string literal are used, where appropriate.

This prevents code from invoking behavior which is unconditionally undefined. The single-argument const CharT* constructor does not check for the null case before dereferencing its input. The standard is slated to add an explicitly-deleted overload to catch some of these cases: wg21.link/p2166

To catch the additional cases of NULL (which expands to __null) and 0, first run the modernize-use-nullptr check to convert the callers to nullptr.

std::string_view sv = nullptr;

sv = nullptr;

bool is_empty = sv == nullptr;
bool isnt_empty = sv != nullptr;

accepts_sv(nullptr);

accepts_sv({{}});  // A

accepts_sv({nullptr, 0});  // B

is translated into...

std::string_view sv = {};

sv = {};

bool is_empty = sv.empty();
bool isnt_empty = !sv.empty();

accepts_sv("");

accepts_sv("");  // A

accepts_sv({nullptr, 0});  // B

NOTE:

The source pattern with trailing comment "A" selects the (const CharT*) constructor overload and then value-initializes the pointer, causing a null dereference. It happens to not include the nullptr literal, but it is still within the scope of this ClangTidy check.

NOTE:

The source pattern with trailing comment "B" selects the (const CharT*, size_type) constructor which is perfectly valid, since the length argument is 0. It is not changed by this ClangTidy check.

The checker detects various cases when an enum is probably misused (as a bitmask ).

1.

When "ADD" or "bitwise OR" is used between two enum which come from different types and these types value ranges are not disjoint.

The following cases will be investigated only using StrictMode. We regard the enum as a (suspicious) bitmask if the three conditions below are true at the same time:

• at most half of the elements of the enum are non pow-of-2 numbers (because of short enumerations)
• there is another non pow-of-2 number than the enum constant representing all choices (the result "bitwise OR" operation of all enum elements)
• enum type variable/enumconstant is used as an argument of a + or "bitwise OR " operator

So whenever the non pow-of-2 element is used as a bitmask element we diagnose a misuse and give a warning.

2.

Investigating the right hand side of += and |= operator.

3.

Check only the enum value side of a | and + operator if one of them is not enum val.

4.

Check both side of | or + operator where the enum values are from the same enum type.

Examples:

enum { A, B, C };
enum { D, E, F = 5 };
enum { G = 10, H = 11, I = 12 };

unsigned flag;
flag =
    A |
    H; // OK, disjoint value intervals in the enum types ->probably good use.
flag = B | F; // Warning, have common values so they are probably misused.

// Case 2:
enum Bitmask {
  A = 0,
  B = 1,
  C = 2,
  D = 4,
  E = 8,
  F = 16,
  G = 31 // OK, real bitmask.
};

enum Almostbitmask {
  AA = 0,
  BB = 1,
  CC = 2,
  DD = 4,
  EE = 8,
  FF = 16,
  GG // Problem, forgot to initialize.
};

unsigned flag = 0;
flag |= E; // OK.
flag |=
    EE; // Warning at the decl, and note that it was used here as a bitmask.

StrictMode

Default value: 0. When non-null the suspicious bitmask usage will be investigated additionally to the different enum usage check.

The check detects various cases when an include refers to what appears to be an implementation file, which often leads to hard-to-track-down ODR violations.

Examples:

#include "Dinosaur.hpp"     // OK, .hpp files tend not to have definitions.
#include "Pterodactyl.h"    // OK, .h files tend not to have definitions.
#include "Velociraptor.cpp" // Warning, filename is suspicious.
#include_next <stdio.c>     // Warning, filename is suspicious.

Finds potentially incorrect calls to memcmp() based on properties of the arguments. The following cases are covered:

Case 1: Non-standard-layout type

Comparing the object representations of non-standard-layout objects may not properly compare the value representations.

Case 2: Types with no unique object representation

Objects with the same value may not have the same object representation. This may be caused by padding or floating-point types.

See also: EXP42-C. Do not compare padding data and FLP37-C. Do not use object representations to compare floating-point values

This check is also related to and partially overlaps the CERT C++ Coding Standard rules OOP57-CPP. Prefer special member functions and overloaded operators to C Standard Library functions and EXP62-CPP. Do not access the bits of an object representation that are not part of the object's value representation

cert-exp42-c redirects here as an alias of this check.

This check finds memset() calls with potential mistakes in their arguments. Considering the function as void* memset(void* destination, int fill_value, size_t byte_count), the following cases are covered:

Case 1: Fill value is a character ``'0'``

Filling up a memory area with ASCII code 48 characters is not customary, possibly integer zeroes were intended instead. The check offers a replacement of '0' with 0. Memsetting character pointers with '0' is allowed.

Case 2: Fill value is truncated

Memset converts fill_value to unsigned char before using it. If fill_value is out of unsigned character range, it gets truncated and memory will not contain the desired pattern.

Case 3: Byte count is zero

Calling memset with a literal zero in its byte_count argument is likely to be unintended and swapped with fill_value. The check offers to swap these two arguments.

Corresponding cpplint.py check name: runtime/memset.

Examples:

void foo() {
  int i[5] = {1, 2, 3, 4, 5};
  int *ip = i;
  char c = '1';
  char *cp = &c;
  int v = 0;

  // Case 1
  memset(ip, '0', 1); // suspicious
  memset(cp, '0', 1); // OK

  // Case 2
  memset(ip, 0xabcd, 1); // fill value gets truncated
  memset(ip, 0x00, 1);   // OK

  // Case 3
  memset(ip, sizeof(int), v); // zero length, potentially swapped
  memset(ip, 0, 1);           // OK
}

String literals placed side-by-side are concatenated at translation phase 6 (after the preprocessor). This feature is used to represent long string literal on multiple lines.

For instance, the following declarations are equivalent:

const char* A[] = "This is a test";
const char* B[] = "This" " is a "    "test";

A common mistake done by programmers is to forget a comma between two string literals in an array initializer list.

const char* Test[] = {
  "line 1",
  "line 2"     // Missing comma!
  "line 3",
  "line 4",
  "line 5"
};

The array contains the string "line 2line3" at offset 1 (i.e. Test[1]). Clang won't generate warnings at compile time.

This check may warn incorrectly on cases like:

const char* SupportedFormat[] = {
  "Error %s",
  "Code " PRIu64,   // May warn here.
  "Warning %s",
};

SizeThreshold

An unsigned integer specifying the minimum size of a string literal to be considered by the check. Default is 5U.

RatioThreshold

A string specifying the maximum threshold ratio [0, 1.0] of suspicious string literals to be considered. Default is ".2".

MaxConcatenatedTokens

An unsigned integer specifying the maximum number of concatenated tokens. Default is 5U.

This check finds usages of realloc where the return value is assigned to the same expression as passed to the first argument: p = realloc(p, size); The problem with this construct is that if realloc fails it returns a null pointer but does not deallocate the original memory. If no other variable is pointing to it, the original memory block is not available any more for the program to use or free. In either case p = realloc(p, size); indicates bad coding style and can be replaced by q = realloc(p, size);.

The pointer expression (used at realloc) can be a variable or a field member of a data structure, but can not contain function calls or unresolved types.

In obvious cases when the pointer used at realloc is assigned to another variable before the realloc call, no warning is emitted. This happens only if a simple expression in form of q = p or void *q = p is found in the same function where p = realloc(p, ...) is found. The assignment has to be before the call to realloc (but otherwise at any place) in the same function. This suppression works only if p is a single variable.

Examples:

struct A {
  void *p;
};

A &getA();

void foo(void *p, A *a, int new_size) {
  p = realloc(p, new_size); // warning: 'p' may be set to null if 'realloc' fails, which may result in a leak of the original buffer
  a->p = realloc(a->p, new_size); // warning: 'a->p' may be set to null if 'realloc' fails, which may result in a leak of the original buffer
  getA().p = realloc(getA().p, new_size); // no warning
}

void foo1(void *p, int new_size) {
  void *p1 = p;
  p = realloc(p, new_size); // no warning
}

Finds most instances of stray semicolons that unexpectedly alter the meaning of the code. More specifically, it looks for if, while, for and for-range statements whose body is a single semicolon, and then analyzes the context of the code (e.g. indentation) in an attempt to determine whether that is intentional.

if (x < y);
{
  x++;
}

Here the body of the if statement consists of only the semicolon at the end of the first line, and x will be incremented regardless of the condition.

while ((line = readLine(file)) != NULL);
  processLine(line);

As a result of this code, processLine() will only be called once, when the while loop with the empty body exits with line == NULL. The indentation of the code indicates the intention of the programmer.

if (x >= y);
x -= y;

While the indentation does not imply any nesting, there is simply no valid reason to have an if statement with an empty body (but it can make sense for a loop). So this check issues a warning for the code above.

To solve the issue remove the stray semicolon or in case the empty body is intentional, reflect this using code indentation or put the semicolon in a new line. For example:

while (readWhitespace());
  Token t = readNextToken();

Here the second line is indented in a way that suggests that it is meant to be the body of the while loop - whose body is in fact empty, because of the semicolon at the end of the first line.

Either remove the indentation from the second line:

while (readWhitespace());
Token t = readNextToken();

... or move the semicolon from the end of the first line to a new line:

while (readWhitespace())
  ;

  Token t = readNextToken();

In this case the check will assume that you know what you are doing, and will not raise a warning.

Find suspicious usage of runtime string comparison functions. This check is valid in C and C++.

Checks for calls with implicit comparator and proposed to explicitly add it.

if (strcmp(...))       // Implicitly compare to zero
if (!strcmp(...))      // Won't warn
if (strcmp(...) != 0)  // Won't warn

Checks that compare function results (i.e., strcmp) are compared to valid constant. The resulting value is

<  0    when lower than,
>  0    when greater than,
== 0    when equals.

A common mistake is to compare the result to 1 or -1.

if (strcmp(...) == -1)  // Incorrect usage of the returned value.

Additionally, the check warns if the results value is implicitly cast to a suspicious non-integer type. It's happening when the returned value is used in a wrong context.

if (strcmp(...) < 0.)  // Incorrect usage of the returned value.

WarnOnImplicitComparison

When true, the check will warn on implicit comparison. true by default.

WarnOnLogicalNotComparison

When true, the check will warn on logical not comparison. false by default.

StringCompareLikeFunctions

A string specifying the comma-separated names of the extra string comparison functions. Default is an empty string. The check will detect the following string comparison functions: __builtin_memcmp, __builtin_strcasecmp, __builtin_strcmp, __builtin_strncasecmp, __builtin_strncmp, _mbscmp, _mbscmp_l, _mbsicmp, _mbsicmp_l, _mbsnbcmp, _mbsnbcmp_l, _mbsnbicmp, _mbsnbicmp_l, _mbsncmp, _mbsncmp_l, _mbsnicmp, _mbsnicmp_l, _memicmp, _memicmp_l, _stricmp, _stricmp_l, _strnicmp, _strnicmp_l, _wcsicmp, _wcsicmp_l, _wcsnicmp, _wcsnicmp_l, lstrcmp, lstrcmpi, memcmp, memicmp, strcasecmp, strcmp, strcmpi, stricmp, strncasecmp, strncmp, strnicmp, wcscasecmp, wcscmp, wcsicmp, wcsncmp, wcsnicmp, wmemcmp.

Identifies suspicious usages of std::string_view::data() that could lead to reading out-of-bounds data due to inadequate or incorrect string null termination.

It warns when the result of data() is passed to a constructor or function without also passing the corresponding result of size() or length() member function. Such usage can lead to unintended behavior, particularly when assuming the data pointed to by data() is null-terminated.

The absence of a c_str() method in std::string_view often leads developers to use data() as a substitute, especially when interfacing with C APIs that expect null-terminated strings. However, since data() does not guarantee null termination, this can result in unintended behavior if the API relies on proper null termination for correct string interpretation.

In today's programming landscape, this scenario can occur when implicitly converting an std::string_view to an std::string. Since the constructor in std::string designed for string-view-like objects is explicit, attempting to pass an std::string_view to a function expecting an std::string will result in a compilation error. As a workaround, developers may be tempted to utilize the .data() method to achieve compilation, introducing potential risks.

For instance:

void printString(const std::string& str) {
  std::cout << "String: " << str << std::endl;
}

void something(std::string_view sv) {
  printString(sv.data());
}

In this example, directly passing sv to the printString function would lead to a compilation error due to the explicit nature of the std::string constructor. Consequently, developers might opt for sv.data() to resolve the compilation error, albeit introducing potential hazards as discussed.

StringViewTypes

Option allows users to specify custom string view-like types for analysis. It accepts a semicolon-separated list of type names or regular expressions matching these types. Default value is: ::std::basic_string_view;::llvm::StringRef.

AllowedCallees

Specifies methods, functions, or classes where the result of .data() is passed to. Allows to exclude such calls from the analysis. Accepts a semicolon-separated list of names or regular expressions matching these entities. Default value is: empty string.

Finds potentially swapped arguments by examining implicit conversions. It analyzes the types of the arguments being passed to a function and compares them to the expected types of the corresponding parameters. If there is a mismatch or an implicit conversion that indicates a potential swap, a warning is raised.

void printNumbers(int a, float b);

int main() {
  // Swapped arguments: float passed as int, int as float)
  printNumbers(10.0f, 5);
  return 0;
}

Covers a wide range of implicit conversions, including: - User-defined conversions - Conversions from floating-point types to boolean or integral types - Conversions from integral types to boolean or floating-point types - Conversions from boolean to integer types or floating-point types - Conversions from (member) pointers to boolean

It is important to note that for most argument swaps, the types need to match exactly. However, there are exceptions to this rule. Specifically, when the swapped argument is of integral type, an exact match is not always necessary. Implicit casts from other integral types are also accepted. Similarly, when dealing with floating-point arguments, implicit casts between different floating-point types are considered acceptable.

To avoid confusion, swaps where both swapped arguments are of integral types or both are of floating-point types do not trigger the warning. In such cases, it's assumed that the developer intentionally used different integral or floating-point types and does not raise a warning. This approach prevents false positives and provides flexibility in handling situations where varying integral or floating-point types are intentionally utilized.

Ensures that switch statements without default cases are flagged, focuses only on covering cases with non-enums where the compiler may not issue warnings.

Switch statements without a default case can lead to unexpected behavior and incomplete handling of all possible cases. When a switch statement lacks a default case, if a value is encountered that does not match any of the specified cases, the program will continue execution without any defined behavior or handling.

This check helps identify switch statements that are missing a default case, allowing developers to ensure that all possible cases are handled properly. Adding a default case allows for graceful handling of unexpected or unmatched values, reducing the risk of program errors and unexpected behavior.

Example:

// Example 1:
// warning: switching on non-enum value without default case may not cover all cases
switch (i) {
case 0:
  break;
}

// Example 2:
enum E { eE1 };
E e = eE1;
switch (e) { // no-warning
case eE1:
  break;
}

// Example 3:
int i = 0;
switch (i) { // no-warning
case 0:
  break;
default:
  break;
}

NOTE:

Enum types are already covered by compiler warnings (comes under -Wswitch) when a switch statement does not handle all enum values. This check focuses on non-enum types where the compiler warnings may not be present.

SEE ALSO:

The CppCoreGuideline ES.79 provide guidelines on switch statements, including the recommendation to always provide a default case.

Detects do while loops with a condition always evaluating to false that have a continue statement, as this continue terminates the loop effectively.

void f() {
do {
  // some code
  continue; // terminating continue
  // some other code
} while(false);

Warns about a potentially missing throw keyword. If a temporary object is created, but the object's type derives from (or is the same as) a class that has 'EXCEPTION', 'Exception' or 'exception' in its name, we can assume that the programmer's intention was to throw that object.

Example:

void f(int i) {
  if (i < 0) {
    // Exception is created but is not thrown.
    std::runtime_error("Unexpected argument");
  }
}

Detects those for loops that have a loop variable with a "too small" type which means this type can't represent all values which are part of the iteration range.

int main() {
  long size = 294967296l;
  for (short i = 0; i < size; ++i) {}
}

This for loop is an infinite loop because the short type can't represent all values in the [0..size] interval.

In a real use case size means a container's size which depends on the user input.

int doSomething(const std::vector& items) {
  for (short i = 0; i < items.size(); ++i) {}
}

This algorithm works for a small amount of objects, but will lead to freeze for a larger user input.

It's recommended to enable the compiler warning -Wtautological-constant-out-of-range-compare as well, since check does not inspect compile-time constant loop boundaries to avoid overlaps with the warning.

MagnitudeBitsUpperLimit

Upper limit for the magnitude bits of the loop variable. If it's set the check filters out those catches in which the loop variable's type has more magnitude bits as the specified upper limit. The default value is 16. For example, if the user sets this option to 31 (bits), then a 32-bit unsigned int is ignored by the check, however a 32-bit int is not (A 32-bit signed int has 31 magnitude bits).

int main() {
  long size = 294967296l;
  for (unsigned i = 0; i < size; ++i) {} // no warning with MagnitudeBitsUpperLimit = 31 on a system where unsigned is 32-bit
  for (int i = 0; i < size; ++i) {} // warning with MagnitudeBitsUpperLimit = 31 on a system where int is 32-bit
}

Note: This check uses a flow-sensitive static analysis to produce its results. Therefore, it may be more resource intensive (RAM, CPU) than the average clang-tidy check.

This check identifies unsafe accesses to values contained in std::optional<T>, absl::optional<T>, base::Optional<T>, or folly::Optional<T> objects. Below we will refer to all these types collectively as optional<T>.

An access to the value of an optional<T> occurs when one of its value, operator*, or operator-> member functions is invoked.  To align with common misconceptions, the check considers these member functions as equivalent, even though there are subtle differences related to exceptions versus undefined behavior. See Additional notes, below, for more information on this topic.

An access to the value of an optional<T> is considered safe if and only if code in the local scope (for example, a function body) ensures that the optional<T> has a value in all possible execution paths that can reach the access. That should happen either through an explicit check, using the optional<T>::has_value member function, or by constructing the optional<T> in a way that shows that it unambiguously holds a value (e.g using std::make_optional which always returns a populated std::optional<T>).

Below we list some examples, starting with unsafe optional access patterns, followed by safe access patterns.

The check flags accesses to the value that are not locally guarded by existence check:

void f(std::optional<int> opt) {
  use(*opt); // unsafe: it is unclear whether `opt` has a value.
}

The check is aware of the state of an optional object in different branches of the code. For example:

void f(std::optional<int> opt) {
  if (opt.has_value()) {
  } else {
    use(opt.value()); // unsafe: it is clear that `opt` does *not* have a value.
  }
}

The check is aware that function results might not be stable. That is, consecutive calls to the same function might return different values. For example:

void f(Foo foo) {
  if (foo.opt().has_value()) {
    use(*foo.opt()); // unsafe: it is unclear whether `foo.opt()` has a value.
  }
}

The check is unaware of invariants of uncommon APIs. For example:

void f(Foo foo) {
  if (foo.HasProperty("bar")) {
    use(*foo.GetProperty("bar")); // unsafe: it is unclear whether `foo.GetProperty("bar")` has a value.
  }
}

The check relies on local reasoning. The check and value access must both happen in the same function. An access is considered unsafe even if the caller of the function performing the access ensures that the optional has a value. For example:

void g(std::optional<int> opt) {
  use(*opt); // unsafe: it is unclear whether `opt` has a value.
}

void f(std::optional<int> opt) {
  if (opt.has_value()) {
    g(opt);
  }
}

The check recognizes all straightforward ways for checking if a value exists and accessing the value contained in an optional object. For example:

void f(std::optional<int> opt) {
  if (opt.has_value()) {
    use(*opt);
  }
}

The criteria that the check uses is semantic, not syntactic. It recognizes when a copy of the optional object being accessed is known to have a value. For example:

void f(std::optional<int> opt1) {
  if (opt1.has_value()) {
    std::optional<int> opt2 = opt1;
    use(*opt2);
  }
}

The check is aware of common macros like CHECK and DCHECK. Those can be used to ensure that an optional object has a value. For example:

void f(std::optional<int> opt) {
  DCHECK(opt.has_value());
  use(*opt);
}

The check is aware of correlated branches in the code and can figure out when an optional object is ensured to have a value on all execution paths that lead to an access. For example:

void f(std::optional<int> opt) {
  bool safe = false;
  if (opt.has_value() && SomeOtherCondition()) {
    safe = true;
  }
  // ... more code...
  if (safe) {
    use(*opt);
  }
}

Since function results are not assumed to be stable across calls, it is best to store the result of the function call in a local variable and use that variable to access the value. For example:

void f(Foo foo) {
  if (const auto& foo_opt = foo.opt(); foo_opt.has_value()) {
    use(*foo_opt);
  }
}

When uncommon APIs guarantee that an optional has contents, do not rely on it -- instead, check explicitly that the optional object has a value. For example:

void f(Foo foo) {
  if (const auto& property = foo.GetProperty("bar")) {
    use(*property);
  }
}

instead of the HasProperty, GetProperty pairing we saw above.

If you know that all of a function's callers have checked that an optional argument has a value, either change the function to take the value directly or check the optional again in the local scope of the callee. For example:

void g(int val) {
  use(val);
}

void f(std::optional<int> opt) {
  if (opt.has_value()) {
    g(*opt);
  }
}

and

struct S {
  std::optional<int> opt;
  int x;
};

void g(const S &s) {
  if (s.opt.has_value() && s.x > 10) {
    use(*s.opt);
}

void f(S s) {
  if (s.opt.has_value()) {
    g(s);
  }
}

The check is aware of aliases of optional types that are created via using declarations. For example:

using OptionalInt = std::optional<int>;

void f(OptionalInt opt) {
  use(opt.value()); // unsafe: it is unclear whether `opt` has a value.
}

The check does not currently report unsafe optional accesses in lambdas. A future version will expand the scope to lambdas, following the rules outlined above. It is best to follow the same principles when using optionals in lambdas.

Given that value() has well-defined behavior (either throwing an exception or terminating the program), why treat it the same as operator*() which causes undefined behavior (UB)? That is, why is it considered unsafe to access an optional with value(), if it's not provably populated with a value?  For that matter, why is CHECK() followed by operator*() any better than value(), given that they are semantically equivalent (on configurations that disable exceptions)?

The answer is that we assume most users do not realize the difference between value() and operator*(). Shifting to operator*() and some form of explicit value-presence check or explicit program termination has two advantages:

• Readability. The check, and any potential side effects like program shutdown, are very clear in the code. Separating access from checks can actually make the checks more obvious.
• Performance. A single check can cover many or even all accesses within scope. This gives the user the best of both worlds -- the safety of a dynamic check, but without incurring redundant costs.

Finds calls of memory manipulation functions memset(), memcpy() and memmove() on non-TriviallyCopyable objects resulting in undefined behavior.

Using memory manipulation functions on non-TriviallyCopyable objects can lead to a range of subtle and challenging issues in C++ code. The most immediate concern is the potential for undefined behavior, where the state of the object may become corrupted or invalid. This can manifest as crashes, data corruption, or unexpected behavior at runtime, making it challenging to identify and diagnose the root cause. Additionally, misuse of memory manipulation functions can bypass essential object-specific operations, such as constructors and destructors, leading to resource leaks or improper initialization.

For example, when using memcpy to copy std::string, pointer data is being copied, and it can result in a double free issue.

#include <cstring>
#include <string>

int main() {
    std::string source = "Hello";
    std::string destination;

    std::memcpy(&destination, &source, sizeof(std::string));

    // Undefined behavior may occur here, during std::string destructor call.
    return 0;
}

Finds creation of temporary objects in constructors that look like a function call to another constructor of the same class.

The user most likely meant to use a delegating constructor or base class initializer.

Finds calls to new with missing exception handler for std::bad_alloc.

Calls to new may throw exceptions of type std::bad_alloc that should be handled. Alternatively, the nonthrowing form of new can be used. The check verifies that the exception is handled in the function that calls new.

If a nonthrowing version is used or the exception is allowed to propagate out of the function no warning is generated.

The exception handler is checked if it catches a std::bad_alloc or std::exception exception type, or all exceptions (catch-all). The check assumes that any user-defined operator new is either noexcept or may throw an exception of type std::bad_alloc (or one derived from it). Other exception class types are not taken into account.

int *f() noexcept {
  int *p = new int[1000]; // warning: missing exception handler for allocation failure at 'new'
  // ...
  return p;
}

int *f1() { // not 'noexcept'
  int *p = new int[1000]; // no warning: exception can be handled outside
                          // of this function
  // ...
  return p;
}

int *f2() noexcept {
  try {
    int *p = new int[1000]; // no warning: exception is handled
    // ...
    return p;
  } catch (std::bad_alloc &) {
    // ...
  }
  // ...
}

int *f3() noexcept {
  int *p = new (std::nothrow) int[1000]; // no warning: "nothrow" is used
  // ...
  return p;
}

cert-oop54-cpp redirects here as an alias for this check. For the CERT alias, the WarnOnlyIfThisHasSuspiciousField option is set to false.

Finds user-defined copy assignment operators which do not protect the code against self-assignment either by checking self-assignment explicitly or using the copy-and-swap or the copy-and-move method.

By default, this check searches only those classes which have any pointer or C array field to avoid false positives. In case of a pointer or a C array, it's likely that self-copy assignment breaks the object if the copy assignment operator was not written with care.

See also: OOP54-CPP. Gracefully handle self-copy assignment

A copy assignment operator must prevent that self-copy assignment ruins the object state. A typical use case is when the class has a pointer field and the copy assignment operator first releases the pointed object and then tries to assign it:

class T {
int* p;

public:
  T(const T &rhs) : p(rhs.p ? new int(*rhs.p) : nullptr) {}
  ~T() { delete p; }

  // ...

  T& operator=(const T &rhs) {
    delete p;
    p = new int(*rhs.p);
    return *this;
  }
};

There are two common C++ patterns to avoid this problem. The first is the self-assignment check:

class T {
int* p;

public:
  T(const T &rhs) : p(rhs.p ? new int(*rhs.p) : nullptr) {}
  ~T() { delete p; }

  // ...

  T& operator=(const T &rhs) {
    if(this == &rhs)
      return *this;

    delete p;
    p = new int(*rhs.p);
    return *this;
  }
};

The second one is the copy-and-swap method when we create a temporary copy (using the copy constructor) and then swap this temporary object with this:

class T {
int* p;

public:
  T(const T &rhs) : p(rhs.p ? new int(*rhs.p) : nullptr) {}
  ~T() { delete p; }

  // ...

  void swap(T &rhs) {
    using std::swap;
    swap(p, rhs.p);
  }

  T& operator=(const T &rhs) {
    T(rhs).swap(*this);
    return *this;
  }
};

There is a third pattern which is less common. Let's call it the copy-and-move method when we create a temporary copy (using the copy constructor) and then move this temporary object into this (needs a move assignment operator):

class T {
int* p;

public:
  T(const T &rhs) : p(rhs.p ? new int(*rhs.p) : nullptr) {}
  ~T() { delete p; }

  // ...

  T& operator=(const T &rhs) {
    T t = rhs;
    *this = std::move(t);
    return *this;
  }

  T& operator=(T &&rhs) {
    p = rhs.p;
    rhs.p = nullptr;
    return *this;
  }
};

WarnOnlyIfThisHasSuspiciousField

When true, the check will warn only if the container class of the copy assignment operator has any suspicious fields (pointer or C array). This option is set to true by default.

Finds initializations of C++ unique pointers to non-array type that are initialized with an array.

If a pointer std::unique_ptr<T> is initialized with a new-expression new T[] the memory is not deallocated correctly. A plain delete is used in this case to deallocate the target memory. Instead a delete[] call is needed. A std::unique_ptr<T[]> uses the correct delete operator. The check does not emit warning if an unique_ptr with user-specified deleter type is used.

The check offers replacement of unique_ptr<T> to unique_ptr<T[]> if it is used at a single variable declaration (one variable in one statement).

Example:

std::unique_ptr<Foo> x(new Foo[10]); // -> std::unique_ptr<Foo[]> x(new Foo[10]);
//                     ^ warning: unique pointer to non-array is initialized with array
std::unique_ptr<Foo> x1(new Foo), x2(new Foo[10]); // no replacement
//                                   ^ warning: unique pointer to non-array is initialized with array

D d;
std::unique_ptr<Foo, D> x3(new Foo[10], d); // no warning (custom deleter used)

struct S {
  std::unique_ptr<Foo> x(new Foo[10]); // no replacement in this case
  //                     ^ warning: unique pointer to non-array is initialized with array
};

This check partially covers the CERT C++ Coding Standard rule MEM51-CPP. Properly deallocate dynamically allocated resources However, only the std::unique_ptr case is detected by this check.

Checks for functions that have safer, more secure replacements available, or are considered deprecated due to design flaws. The check heavily relies on the functions from the Annex K. "Bounds-checking interfaces" of C11.

The check implements the following rules from the CERT C Coding Standard:

• Recommendation MSC24-C. Do not use deprecated or obsolescent functions.
• Rule MSC33-C. Do not pass invalid data to the asctime() function.

cert-msc24-c and cert-msc33-c redirect here as aliases of this check.

If Annex K. is available, a replacement from Annex K. is suggested for the following functions:

asctime, asctime_r, bsearch, ctime, fopen, fprintf, freopen, fscanf, fwprintf, fwscanf, getenv, gets, gmtime, localtime, mbsrtowcs, mbstowcs, memcpy, memmove, memset, printf, qsort, scanf,  snprintf, sprintf,  sscanf, strcat, strcpy, strerror, strlen, strncat, strncpy, strtok, swprintf, swscanf, vfprintf, vfscanf, vfwprintf, vfwscanf, vprintf, vscanf, vsnprintf, vsprintf, vsscanf, vswprintf, vswscanf, vwprintf, vwscanf, wcrtomb, wcscat, wcscpy, wcslen, wcsncat, wcsncpy, wcsrtombs, wcstok, wcstombs, wctomb, wmemcpy, wmemmove, wprintf, wscanf.

If Annex K. is not available, replacements are suggested only for the following functions from the previous list:

• asctime, asctime_r, suggested replacement: strftime
• gets, suggested replacement: fgets

The following functions are always checked, regardless of Annex K availability:

• rewind, suggested replacement: fseek
• setbuf, suggested replacement: setvbuf

If ReportMoreUnsafeFunctions is enabled, the following functions are also checked:

• bcmp, suggested replacement: memcmp
• bcopy, suggested replacement: memcpy_s if Annex K is available, or memcpy
• bzero, suggested replacement: memset_s if Annex K is available, or memset
• getpw, suggested replacement: getpwuid
• vfork, suggested replacement: posix_spawn

Although mentioned in the associated CERT rules, the following functions are ignored by the check:

atof, atoi, atol, atoll, tmpfile.

The availability of Annex K is determined based on the following macros:

• __STDC_LIB_EXT1__: feature macro, which indicates the presence of Annex K. "Bounds-checking interfaces" in the library implementation
• __STDC_WANT_LIB_EXT1__: user-defined macro, which indicates that the user requests the functions from Annex K. to be defined.

Both macros have to be defined to suggest replacement functions from Annex K. __STDC_LIB_EXT1__ is defined by the library implementation, and __STDC_WANT_LIB_EXT1__ must be defined to 1 by the user before including any system headers.

ReportMoreUnsafeFunctions

When true, additional functions from widely used APIs (such as POSIX) are added to the list of reported functions. See the main documentation of the check for the complete list as to what this option enables. Default is true.

#ifndef __STDC_LIB_EXT1__
#error "Annex K is not supported by the current standard library implementation."
#endif

#define __STDC_WANT_LIB_EXT1__ 1

#include <string.h> // Defines functions from Annex K.
#include <stdio.h>

enum { BUFSIZE = 32 };

void Unsafe(const char *Msg) {
  static const char Prefix[] = "Error: ";
  static const char Suffix[] = "\n";
  char Buf[BUFSIZE] = {0};

  strcpy(Buf, Prefix); // warning: function 'strcpy' is not bounds-checking; 'strcpy_s' should be used instead.
  strcat(Buf, Msg);    // warning: function 'strcat' is not bounds-checking; 'strcat_s' should be used instead.
  strcat(Buf, Suffix); // warning: function 'strcat' is not bounds-checking; 'strcat_s' should be used instead.
  if (fputs(buf, stderr) < 0) {
    // error handling
    return;
  }
}

void UsingSafeFunctions(const char *Msg) {
  static const char Prefix[] = "Error: ";
  static const char Suffix[] = "\n";
  char Buf[BUFSIZE] = {0};

  if (strcpy_s(Buf, BUFSIZE, Prefix) != 0) {
    // error handling
    return;
  }

  if (strcat_s(Buf, BUFSIZE, Msg) != 0) {
    // error handling
    return;
  }

  if (strcat_s(Buf, BUFSIZE, Suffix) != 0) {
    // error handling
    return;
  }

  if (fputs(Buf, stderr) < 0) {
    // error handling
    return;
  }
}

Warns when a local non trivial variable is unused within a function. The following types of variables are excluded from this check:

• trivial and trivially copyable
• references and pointers
• exception variables in catch clauses
• static or thread local
• structured bindings
• variables with [[maybe_unused]] attribute

This check can be configured to warn on all non-trivial variables by setting IncludeTypes to .*, and excluding specific types using ExcludeTypes.

In the this example, my_lock would generate a warning that it is unused.

std::mutex my_lock;
// my_lock local variable is never used

In the next example, future2 would generate a warning that it is unused.

std::future<MyObject> future1;
std::future<MyObject> future2;
// ...
MyObject foo = future1.get();
// future2 is not used.

IncludeTypes

Semicolon-separated list of regular expressions matching types of variables to check. By default the following types are checked:

• ::std::.*mutex
• ::std::future
• ::std::basic_string
• ::std::basic_regex
• ::std::basic_istringstream
• ::std::basic_stringstream
• ::std::bitset
• ::std::filesystem::path

ExcludeTypes

A semicolon-separated list of regular expressions matching types that are excluded from the IncludeTypes matches. By default it is an empty list.

Finds temporaries that look like RAII objects.

The canonical example for this is a scoped lock.

{
  scoped_lock(&global_mutex);
  critical_section();
}

The destructor of the scoped_lock is called before the critical_section is entered, leaving it unprotected.

We apply a number of heuristics to reduce the false positive count of this check:

• Ignore code expanded from macros. Testing frameworks make heavy use of this.
• Ignore types with trivial destructors. They are very unlikely to be RAII objects and there's no difference when they are deleted.
• Ignore objects at the end of a compound statement (doesn't change behavior).
• Ignore objects returned from a call.

Warns on unused function return values. The checked functions can be configured.

Operator overloading with assignment semantics are ignored.

CheckedFunctions

Semicolon-separated list of functions to check. This parameter supports regexp. The function is checked if the name and scope matches, with any arguments. By default the following functions are checked: ^::std::async$, ^::std::launder$, ^::std::remove$, ^::std::remove_if$, ^::std::unique$, ^::std::unique_ptr::release$, ^::std::basic_string::empty$, ^::std::vector::empty$, ^::std::back_inserter$, ^::std::distance$, ^::std::find$, ^::std::find_if$, ^::std::inserter$, ^::std::lower_bound$, ^::std::make_pair$, ^::std::map::count$, ^::std::map::find$, ^::std::map::lower_bound$, ^::std::multimap::equal_range$, ^::std::multimap::upper_bound$, ^::std::set::count$, ^::std::set::find$, ^::std::setfill$, ^::std::setprecision$, ^::std::setw$, ^::std::upper_bound$, ^::std::vector::at$, ^::bsearch$, ^::ferror$, ^::feof$, ^::isalnum$, ^::isalpha$, ^::isblank$, ^::iscntrl$, ^::isdigit$, ^::isgraph$, ^::islower$, ^::isprint$, ^::ispunct$, ^::isspace$, ^::isupper$, ^::iswalnum$, ^::iswprint$, ^::iswspace$, ^::isxdigit$, ^::memchr$, ^::memcmp$, ^::strcmp$, ^::strcoll$, ^::strncmp$, ^::strpbrk$, ^::strrchr$, ^::strspn$, ^::strstr$, ^::wcscmp$, ^::access$, ^::bind$, ^::connect$, ^::difftime$, ^::dlsym$, ^::fnmatch$, ^::getaddrinfo$, ^::getopt$, ^::htonl$, ^::htons$, ^::iconv_open$, ^::inet_addr$, isascii$, isatty$, ^::mmap$, ^::newlocale$, ^::openat$, ^::pathconf$, ^::pthread_equal$, ^::pthread_getspecific$, ^::pthread_mutex_trylock$, ^::readdir$, ^::readlink$, ^::recvmsg$, ^::regexec$, ^::scandir$, ^::semget$, ^::setjmp$, ^::shm_open$, ^::shmget$, ^::sigismember$, ^::strcasecmp$, ^::strsignal$, ^::ttyname$

• std::async(). Not using the return value makes the call synchronous.
• std::launder(). Not using the return value usually means that the function interface was misunderstood by the programmer. Only the returned pointer is "laundered", not the argument.
• std::remove(), std::remove_if() and std::unique(). The returned iterator indicates the boundary between elements to keep and elements to be removed. Not using the return value means that the information about which elements to remove is lost.
• std::unique_ptr::release(). Not using the return value can lead to resource leaks if the same pointer isn't stored anywhere else. Often, ignoring the release() return value indicates that the programmer confused the function with reset().
• std::basic_string::empty() and std::vector::empty(). Not using the return value often indicates that the programmer confused the function with clear().

CheckedReturnTypes

Semicolon-separated list of function return types to check. By default the following function return types are checked: ^::std::error_code$, ^::std::error_condition$, ^::std::errc$, ^::std::expected$, ^::boost::system::error_code$

AllowCastToVoid

Controls whether casting return values to void is permitted. Default: false.

cert-err33-c is an alias of this check that checks a fixed and large set of standard library functions.

Warns if an object is used after it has been moved, for example:

std::string str = "Hello, world!\n";
std::vector<std::string> messages;
messages.emplace_back(std::move(str));
std::cout << str;

The last line will trigger a warning that str is used after it has been moved.

The check does not trigger a warning if the object is reinitialized after the move and before the use. For example, no warning will be output for this code:

messages.emplace_back(std::move(str));
str = "Greetings, stranger!\n";
std::cout << str;

Subsections below explain more precisely what exactly the check considers to be a move, use, and reinitialization.

The check takes control flow into account. A warning is only emitted if the use can be reached from the move. This means that the following code does not produce a warning:

if (condition) {
  messages.emplace_back(std::move(str));
} else {
  std::cout << str;
}

On the other hand, the following code does produce a warning:

for (int i = 0; i < 10; ++i) {
  std::cout << str;
  messages.emplace_back(std::move(str));
}

(The use-after-move happens on the second iteration of the loop.)

In some cases, the check may not be able to detect that two branches are mutually exclusive. For example (assuming that i is an int):

if (i == 1) {
  messages.emplace_back(std::move(str));
}
if (i == 2) {
  std::cout << str;
}

In this case, the check will erroneously produce a warning, even though it is not possible for both the move and the use to be executed. More formally, the analysis is flow-sensitive but not path-sensitive.

An erroneous warning can be silenced by reinitializing the object after the move:

if (i == 1) {
  messages.emplace_back(std::move(str));
  str = "";
}
if (i == 2) {
  std::cout << str;
}

If you want to avoid the overhead of actually reinitializing the object, you can create a dummy function that causes the check to assume the object was reinitialized:

template <class T>
void IS_INITIALIZED(T&) {}

You can use this as follows:

if (i == 1) {
  messages.emplace_back(std::move(str));
}
if (i == 2) {
  IS_INITIALIZED(str);
  std::cout << str;
}

The check will not output a warning in this case because passing the object to a function as a non-const pointer or reference counts as a reinitialization (see section Reinitialization below).

In many cases, C++ does not make any guarantees about the order in which sub-expressions of a statement are evaluated. This means that in code like the following, it is not guaranteed whether the use will happen before or after the move:

void f(int i, std::vector<int> v);
std::vector<int> v = { 1, 2, 3 };
f(v[1], std::move(v));

In this kind of situation, the check will note that the use and move are unsequenced.

The check will also take sequencing rules into account when reinitializations occur in the same statement as moves or uses. A reinitialization is only considered to reinitialize a variable if it is guaranteed to be evaluated after the move and before the use.

The check currently only considers calls of std::move on local variables or function parameters. It does not check moves of member variables or global variables.

Any call of std::move on a variable is considered to cause a move of that variable, even if the result of std::move is not passed to an rvalue reference parameter.

This means that the check will flag a use-after-move even on a type that does not define a move constructor or move assignment operator. This is intentional. Developers may use std::move on such a type in the expectation that the type will add move semantics in the future. If such a std::move has the potential to cause a use-after-move, we want to warn about it even if the type does not implement move semantics yet.

Furthermore, if the result of std::move is passed to an rvalue reference parameter, this will always be considered to cause a move, even if the function that consumes this parameter does not move from it, or if it does so only conditionally. For example, in the following situation, the check will assume that a move always takes place:

std::vector<std::string> messages;
void f(std::string &&str) {
  // Only remember the message if it isn't empty.
  if (!str.empty()) {
    messages.emplace_back(std::move(str));
  }
}
std::string str = "";
f(std::move(str));

The check will assume that the last line causes a move, even though, in this particular case, it does not. Again, this is intentional.

There is one special case: A call to std::move inside a try_emplace call is conservatively assumed not to move. This is to avoid spurious warnings, as the check has no way to reason about the bool returned by try_emplace.

When analyzing the order in which moves, uses and reinitializations happen (see section Unsequenced moves, uses, and reinitializations), the move is assumed to occur in whichever function the result of the std::move is passed to.

The check also handles perfect-forwarding with std::forward so the following code will also trigger a use-after-move warning.

void consume(int);

void f(int&& i) {
  consume(std::forward<int>(i));
  consume(std::forward<int>(i)); // use-after-move
}

Any occurrence of the moved variable that is not a reinitialization (see below) is considered to be a use.

An exception to this are objects of type std::unique_ptr, std::shared_ptr and std::weak_ptr, which have defined move behavior (objects of these classes are guaranteed to be empty after they have been moved from). Therefore, an object of these classes will only be considered to be used if it is dereferenced, i.e. if operator*, operator-> or operator[] (in the case of std::unique_ptr<T []>) is called on it.

If multiple uses occur after a move, only the first of these is flagged.

The check considers a variable to be reinitialized in the following cases:

• The variable occurs on the left-hand side of an assignment.
• The variable is passed to a function as a non-const pointer or non-const lvalue reference. (It is assumed that the variable may be an out-parameter for the function.)
• clear() or assign() is called on the variable and the variable is of one of the standard container types basic_string, vector, deque, forward_list, list, set, map, multiset, multimap, unordered_set, unordered_map, unordered_multiset, unordered_multimap.
• reset() is called on the variable and the variable is of type std::unique_ptr, std::shared_ptr or std::weak_ptr.
• A member function marked with the [[clang::reinitializes]] attribute is called on the variable.

If the variable in question is a struct and an individual member variable of that struct is written to, the check does not consider this to be a reinitialization -- even if, eventually, all member variables of the struct are written to. For example:

struct S {
  std::string str;
  int i;
};
S s = { "Hello, world!\n", 42 };
S s_other = std::move(s);
s.str = "Lorem ipsum";
s.i = 99;

The check will not consider s to be reinitialized after the last line; instead, the line that assigns to s.str will be flagged as a use-after-move. This is intentional as this pattern of reinitializing a struct is error-prone. For example, if an additional member variable is added to S, it is easy to forget to add the reinitialization for this additional member. Instead, it is safer to assign to the entire struct in one go, and this will also avoid the use-after-move warning.

Warn if a function is a near miss (i.e. the name is very similar and the function signature is the same) to a virtual function from a base class.

Example:

struct Base {
  virtual void func();
};

struct Derived : Base {
  virtual void funk();
  // warning: 'Derived::funk' has a similar name and the same signature as virtual method 'Base::func'; did you mean to override it?
};

The cert-con36-c check is an alias, please see bugprone-spuriously-wake-up-functions for more information.

The cert-con54-cpp check is an alias, please see bugprone-spuriously-wake-up-functions for more information.

The cert-ctr56-cpp check is an alias, please see bugprone-pointer-arithmetic-on-polymorphic-object for more information.

The cert-dcl03-c check is an alias, please see misc-static-assert for more information.

The cert-dcl16-c check is an alias, please see readability-uppercase-literal-suffix for more information.

The cert-dcl37-c check is an alias, please see bugprone-reserved-identifier for more information.

This check flags all function definitions (but not declarations) of C-style variadic functions.

This check corresponds to the CERT C++ Coding Standard rule DCL50-CPP. Do not define a C-style variadic function.

The cert-dcl51-cpp check is an alias, please see bugprone-reserved-identifier for more information.

The cert-dcl54-cpp check is an alias, please see misc-new-delete-overloads for more information.

Modification of the std or posix namespace can result in undefined behavior. This check warns for such modifications. The std (or posix) namespace is allowed to be extended with (class or function) template specializations that depend on an user-defined type (a type that is not defined in the standard system headers).

The check detects the following (user provided) declarations in namespace std or posix:

• Anything that is not a template specialization.
• Explicit specializations of any standard library function template or class template, if it does not have any user-defined type as template argument.
• Explicit specializations of any member function of a standard library class template.
• Explicit specializations of any member function template of a standard library class or class template.
• Explicit or partial specialization of any member class template of a standard library class or class template.

Examples:

namespace std {
  int x; // warning: modification of 'std' namespace can result in undefined behavior [cert-dcl58-cpp]
}

namespace posix::a { // warning: modification of 'posix' namespace can result in undefined behavior
}

template <>
struct ::std::hash<long> { // warning: modification of 'std' namespace can result in undefined behavior
  unsigned long operator()(const long &K) const {
    return K;
  }
};

struct MyData { long data; };

template <>
struct ::std::hash<MyData> { // no warning: specialization with user-defined type
  unsigned long operator()(const MyData &K) const {
    return K.data;
  }
};

namespace std {
  template <>
  void swap<bool>(bool &a, bool &b); // warning: modification of 'std' namespace can result in undefined behavior

  template <>
  bool less<void>::operator()<MyData &&, MyData &&>(MyData &&, MyData &&) const { // warning: modification of 'std' namespace can result in undefined behavior
    return true;
  }
}

This check corresponds to the CERT C++ Coding Standard rule DCL58-CPP. Do not modify the standard namespaces.

The cert-dcl59-cpp check is an alias, please see google-build-namespaces for more information.

This check flags calls to system(), popen(), and _popen(), which execute a command processor. It does not flag calls to system() with a null pointer argument, as such a call checks for the presence of a command processor but does not actually attempt to execute a command.

This check corresponds to the CERT C Coding Standard rule ENV33-C. Do not call system().

The cert-err09-cpp check is an alias, please see misc-throw-by-value-catch-by-reference for more information.

This check corresponds to the CERT C++ Coding Standard recommendation ERR09-CPP. Throw anonymous temporaries. However, all of the CERT recommendations have been removed from public view, and so their justification for the behavior of this check requires an account on their wiki to view.

Warns on unused function return values. Many of the standard library functions return a value that indicates if the call was successful. Ignoring the returned value can cause unexpected behavior if an error has occurred. The following functions are checked:

• aligned_alloc()
• asctime_s()
• at_quick_exit()
• atexit()
• bsearch()
• bsearch_s()
• btowc()
• c16rtomb()
• c32rtomb()
• calloc()
• clock()
• cnd_broadcast()
• cnd_init()
• cnd_signal()
• cnd_timedwait()
• cnd_wait()
• ctime_s()
• fclose()
• fflush()
• fgetc()
• fgetpos()
• fgets()
• fgetwc()
• fopen()
• fopen_s()
• fprintf()
• fprintf_s()
• fputc()
• fputs()
• fputwc()
• fputws()
• fread()
• freopen()
• freopen_s()
• fscanf()
• fscanf_s()
• fseek()
• fsetpos()
• ftell()
• fwprintf()
• fwprintf_s()
• fwrite()
• fwscanf()
• fwscanf_s()
• getc()
• getchar()
• getenv()
• getenv_s()
• gets_s()
• getwc()
• getwchar()
• gmtime()
• gmtime_s()
• localtime()
• localtime_s()
• malloc()
• mbrtoc16()
• mbrtoc32()
• mbsrtowcs()
• mbsrtowcs_s()
• mbstowcs()
• mbstowcs_s()
• memchr()
• mktime()
• mtx_init()
• mtx_lock()
• mtx_timedlock()
• mtx_trylock()
• mtx_unlock()
• printf_s()
• putc()
• putwc()
• raise()
• realloc()
• remove()
• rename()
• setlocale()
• setvbuf()
• scanf()
• scanf_s()
• signal()
• snprintf()
• snprintf_s()
• sprintf()
• sprintf_s()
• sscanf()
• sscanf_s()
• strchr()
• strerror_s()
• strftime()
• strpbrk()
• strrchr()
• strstr()
• strtod()
• strtof()
• strtoimax()
• strtok()
• strtok_s()
• strtol()
• strtold()
• strtoll()
• strtoumax()
• strtoul()
• strtoull()
• strxfrm()
• swprintf()
• swprintf_s()
• swscanf()
• swscanf_s()
• thrd_create()
• thrd_detach()
• thrd_join()
• thrd_sleep()
• time()
• timespec_get()
• tmpfile()
• tmpfile_s()
• tmpnam()
• tmpnam_s()
• tss_create()
• tss_get()
• tss_set()
• ungetc()
• ungetwc()
• vfprintf()
• vfprintf_s()
• vfscanf()
• vfscanf_s()
• vfwprintf()
• vfwprintf_s()
• vfwscanf()
• vfwscanf_s()
• vprintf_s()
• vscanf()
• vscanf_s()
• vsnprintf()
• vsnprintf_s()
• vsprintf()
• vsprintf_s()
• vsscanf()
• vsscanf_s()
• vswprintf()
• vswprintf_s()
• vswscanf()
• vswscanf_s()
• vwprintf_s()
• vwscanf()
• vwscanf_s()
• wcrtomb()
• wcschr()
• wcsftime()
• wcspbrk()
• wcsrchr()
• wcsrtombs()
• wcsrtombs_s()
• wcsstr()
• wcstod()
• wcstof()
• wcstoimax()
• wcstok()
• wcstok_s()
• wcstol()
• wcstold()
• wcstoll()
• wcstombs()
• wcstombs_s()
• wcstoumax()
• wcstoul()
• wcstoull()
• wcsxfrm()
• wctob()
• wctrans()
• wctype()
• wmemchr()
• wprintf_s()
• wscanf()
• wscanf_s()

This check is an alias of check bugprone-unused-return-value with a fixed set of functions.

Suppressing issues by casting to void is enabled by default and can be disabled by setting AllowCastToVoid option to false.

The check corresponds to a part of CERT C Coding Standard rule ERR33-C. Detect and handle standard library errors. The list of checked functions is taken from the rule, with following exception:

• The check can not differentiate if a function is called with NULL argument. Therefore the following functions are not checked: mblen, mbrlen, mbrtowc, mbtowc, wctomb, wctomb_s

This check flags calls to string-to-number conversion functions that do not verify the validity of the conversion, such as atoi() or scanf(). It does not flag calls to strtol(), or other, related conversion functions that do perform better error checking.

#include <stdlib.h>

void func(const char *buff) {
  int si;

  if (buff) {
    si = atoi(buff); /* 'atoi' used to convert a string to an integer, but function will
                         not report conversion errors; consider using 'strtol' instead. */
  } else {
    /* Handle error */
  }
}

This check corresponds to the CERT C Coding Standard rule ERR34-C. Detect errors when converting a string to a number.

This check flags all call expressions involving setjmp() and longjmp().

This check corresponds to the CERT C++ Coding Standard rule ERR52-CPP. Do not use setjmp() or longjmp().

This check flags all static or thread_local variable declarations where the initializer for the object may throw an exception.

This check corresponds to the CERT C++ Coding Standard rule ERR58-CPP. Handle all exceptions thrown before main() begins executing.

This check flags all throw expressions where the exception object is not nothrow copy constructible.

This check corresponds to the CERT C++ Coding Standard rule ERR60-CPP. Exception objects must be nothrow copy constructible.

The cert-err61-cpp check is an alias, please see misc-throw-by-value-catch-by-reference for more information.

The cert-exp42-c check is an alias, please see bugprone-suspicious-memory-comparison for more information.

The cert-fio38-c check is an alias, please see misc-non-copyable-objects for more information.

This check flags for loops where the induction expression has a floating-point type.

This check corresponds to the CERT C Coding Standard rule FLP30-C. Do not use floating-point variables as loop counters.

The cert-flp37-c check is an alias, please see bugprone-suspicious-memory-comparison for more information.

The cert-int09-c check is an alias, please see readability-enum-initial-value for more information.

This check flags uses of default operator new where the type has extended alignment (an alignment greater than the fundamental alignment). (The default operator new is guaranteed to provide the correct alignment if the requested alignment is less or equal to the fundamental alignment). Only cases are detected (by design) where the operator new is not user-defined and is not a placement new (the reason is that in these cases we assume that the user provided the correct memory allocation).

This check corresponds to the CERT C++ Coding Standard rule MEM57-CPP. Avoid using default operator new for over-aligned types.

The cert-msc24-c check is an alias, please see bugprone-unsafe-functions for more information.

The cert-msc30-c check is an alias, please see cert-msc50-cpp for more information.

The cert-msc32-c check is an alias, please see cert-msc51-cpp for more information.

The cert-msc33-c check is an alias, please see bugprone-unsafe-functions for more information.

Pseudorandom number generators use mathematical algorithms to produce a sequence of numbers with good statistical properties, but the numbers produced are not genuinely random. The std::rand() function takes a seed (number), runs a mathematical operation on it and returns the result. By manipulating the seed the result can be predictable. This check warns for the usage of std::rand().

This check flags all pseudo-random number engines, engine adaptor instantiations and srand() when initialized or seeded with default argument, constant expression or any user-configurable type. Pseudo-random number engines seeded with a predictable value may cause vulnerabilities e.g. in security protocols. This is a CERT security rule, see MSC51-CPP. Ensure your random number generator is properly seeded and MSC32-C. Properly seed pseudorandom number generators.

Examples:

void foo() {
  std::mt19937 engine1; // Diagnose, always generate the same sequence
  std::mt19937 engine2(1); // Diagnose
  engine1.seed(); // Diagnose
  engine2.seed(1); // Diagnose

  std::time_t t;
  engine1.seed(std::time(&t)); // Diagnose, system time might be controlled by user

  int x = atoi(argv[1]);
  std::mt19937 engine3(x);  // Will not warn
}

DisallowedSeedTypes

A comma-separated list of the type names which are disallowed. Default values are time_t, std::time_t.

The cert-msc54-cpp check is an alias, please see bugprone-signal-handler for more information.

The cert-oop11-cpp check is an alias, please see performance-move-constructor-init for more information.

This check corresponds to the CERT C++ Coding Standard recommendation OOP11-CPP. Do not copy-initialize members or base classes from a move constructor. However, all of the CERT recommendations have been removed from public view, and so their justification for the behavior of this check requires an account on their wiki to view.

The cert-oop54-cpp check is an alias, please see bugprone-unhandled-self-assignment for more information.

MemSetNames

Specify extra functions to flag that act similarly to memset. Specify names in a semicolon delimited list. Default is an empty string. The check will detect the following functions: memset, std::memset.

MemCpyNames

Specify extra functions to flag that act similarly to memcpy. Specify names in a semicolon delimited list. Default is an empty string. The check will detect the following functions: std::memcpy, memcpy, std::memmove, memmove, std::strcpy, strcpy, memccpy, stpncpy, strncpy.

MemCmpNames

Specify extra functions to flag that act similarly to memcmp. Specify names in a semicolon delimited list. Default is an empty string. The check will detect the following functions: std::memcmp, memcmp, std::strcmp, strcmp, strncmp.

This check corresponds to the CERT C++ Coding Standard rule OOP57-CPP. Prefer special member functions and overloaded operators to C Standard Library functions.

Finds assignments to the copied object and its direct or indirect members in copy constructors and copy assignment operators.

This check corresponds to the CERT C Coding Standard rule OOP58-CPP. Copy operations must not mutate the source object.

The cert-pos44-c check is an alias, please see bugprone-bad-signal-to-kill-thread for more information.

The cert-pos47-c check is an alias, please see concurrency-thread-canceltype-asynchronous for more information.

The cert-sig30-c check is an alias, please see bugprone-signal-handler for more information.

The cert-str34-c check is an alias, please see bugprone-signed-char-misuse for more information.

Finds cases where bitwise shift operation causes undefined behaviour.

The clang-analyzer-core.BitwiseShift check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for logical errors for function calls and Objective-C message expressions (e.g., uninitialized arguments, null function pointers).

The clang-analyzer-core.CallAndMessage check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for division by zero.

The clang-analyzer-core.DivideZero check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for null pointers passed as arguments to a function whose arguments are references or marked with the 'nonnull' attribute.

The clang-analyzer-core.NonNullParamChecker check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for dereferences of null pointers.

The clang-analyzer-core.NullDereference check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check that addresses to stack memory do not escape the function.

The clang-analyzer-core.StackAddressEscape check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for undefined results of binary operators.

The clang-analyzer-core.UndefinedBinaryOperatorResult check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for declarations of VLA of undefined or zero size.

The clang-analyzer-core.VLASize check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for uninitialized values used as array subscripts.

The clang-analyzer-core.uninitialized.ArraySubscript check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for assigning uninitialized values.

The clang-analyzer-core.uninitialized.Assign check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for uninitialized values used as branch conditions.

The clang-analyzer-core.uninitialized.Branch check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for blocks that capture uninitialized values.

The clang-analyzer-core.uninitialized.CapturedBlockVariable check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check if the size of the array in a new[] expression is undefined.

The clang-analyzer-core.uninitialized.NewArraySize check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for uninitialized values being returned to the caller.

The clang-analyzer-core.uninitialized.UndefReturn check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Reports destructions of arrays of polymorphic objects that are destructed as their base class.

The clang-analyzer-cplusplus.ArrayDelete check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for inner pointers of C++ containers used after re/deallocation.

The clang-analyzer-cplusplus.InnerPointer check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Find use-after-move bugs in C++.

The clang-analyzer-cplusplus.Move check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for double-free and use-after-free problems. Traces memory managed by new/delete.

The clang-analyzer-cplusplus.NewDelete check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for memory leaks. Traces memory managed by new/delete.

The clang-analyzer-cplusplus.NewDeleteLeaks check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check if default placement new is provided with pointers to sufficient storage capacity.

The clang-analyzer-cplusplus.PlacementNew check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check pure virtual function calls during construction/destruction.

The clang-analyzer-cplusplus.PureVirtualCall check is an alias of Clang Static Analyzer cplusplus.PureVirtualCall.

Checks C++ std::string bugs.

The clang-analyzer-cplusplus.StringChecker check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for values stored to variables that are never read afterwards.

The clang-analyzer-deadcode.DeadStores check is an alias, please see Clang Static Analyzer Available Checkers for more information.

A Checker that detect leaks related to Fuchsia handles.

The clang-analyzer-fuchsia.HandleChecker check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warns when a null pointer is passed to a pointer which has a _Nonnull type.

The clang-analyzer-nullability.NullPassedToNonnull check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warns when a null pointer is returned from a function that has _Nonnull return type.

The clang-analyzer-nullability.NullReturnedFromNonnull check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warns when a nullable pointer is dereferenced.

The clang-analyzer-nullability.NullableDereferenced check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warns when a nullable pointer is passed to a pointer which has a _Nonnull type.

The clang-analyzer-nullability.NullablePassedToNonnull check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warns when a nullable pointer is returned from a function that has _Nonnull return type.

The clang-analyzer-nullability.NullableReturnedFromNonnull check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check integer to enumeration casts for out of range values.

The clang-analyzer-optin.core.EnumCastOutOfRange check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Reports uninitialized fields after object construction.

The clang-analyzer-optin.cplusplus.UninitializedObject check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check virtual function calls during construction/destruction.

The clang-analyzer-optin.cplusplus.VirtualCall check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Checks MPI code.

The clang-analyzer-optin.mpi.MPI-Checker check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Checker for C-style casts of OSObjects.

The clang-analyzer-optin.osx.OSObjectCStyleCast check is an alias of Clang Static Analyzer optin.osx.OSObjectCStyleCast.

Check that NSLocalizedString macros include a comment for context.

The clang-analyzer-optin.osx.cocoa.localizability.EmptyLocalizationContextChecker check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warns about uses of non-localized NSStrings passed to UI methods expecting localized NSStrings.

The clang-analyzer-optin.osx.cocoa.localizability.NonLocalizedStringChecker check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for performance anti-patterns when using Grand Central Dispatch.

The clang-analyzer-optin.performance.GCDAntipattern check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for excessively padded structs.

The clang-analyzer-optin.performance.Padding check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Finds implementation-defined behavior in UNIX/Posix functions.

The clang-analyzer-optin.portability.UnixAPI check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for memory allocations, where the size parameter might be a tainted (attacker controlled) value.

The clang-analyzer-optin.taint.TaintedAlloc check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for proper uses of various Apple APIs.

The clang-analyzer-osx.API check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Find violations of the Mach Interface Generator calling convention.

The clang-analyzer-osx.MIG check is an alias of Clang Static Analyzer osx.MIG.

Check for erroneous conversions of objects representing numbers into numbers.

The clang-analyzer-osx.NumberObjectConversion check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for leaks and improper reference count management for OSObject.

The clang-analyzer-osx.OSObjectRetainCount check is an alias of Clang Static Analyzer osx.OSObjectRetainCount.

Check for proper uses of Objective-C properties.

The clang-analyzer-osx.ObjCProperty check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for proper uses of Secure Keychain APIs.

The clang-analyzer-osx.SecKeychainAPI check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for nil pointers used as mutexes for @synchronized.

The clang-analyzer-osx.cocoa.AtSync check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn about potentially crashing writes to autoreleasing objects from different autoreleasing pools in Objective-C.

The clang-analyzer-osx.cocoa.AutoreleaseWrite check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for sending 'retain', 'release', or 'autorelease' directly to a Class.

The clang-analyzer-osx.cocoa.ClassRelease check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn about Objective-C classes that lack a correct implementation of -dealloc.

The clang-analyzer-osx.cocoa.Dealloc check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn about Objective-C method signatures with type incompatibilities.

The clang-analyzer-osx.cocoa.IncompatibleMethodTypes check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Improved modeling of loops using Cocoa collection types.

The clang-analyzer-osx.cocoa.Loops check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn about Objective-C methods that lack a necessary call to super.

The clang-analyzer-osx.cocoa.MissingSuperCall check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn for suboptimal uses of NSAutoreleasePool in Objective-C GC mode.

The clang-analyzer-osx.cocoa.NSAutoreleasePool check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check usage of NSError** parameters.

The clang-analyzer-osx.cocoa.NSError check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for prohibited nil arguments to ObjC method calls.

The clang-analyzer-osx.cocoa.NilArg check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Model the APIs that are guaranteed to return a non-nil value.

The clang-analyzer-osx.cocoa.NonNilReturnValue check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for type errors when using Objective-C generics.

The clang-analyzer-osx.cocoa.ObjCGenerics check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for leaks and improper reference count management.

The clang-analyzer-osx.cocoa.RetainCount check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for leaked memory in autorelease pools that will never be drained.

The clang-analyzer-osx.cocoa.RunLoopAutoreleaseLeak check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check that 'self' is properly initialized inside an initializer method.

The clang-analyzer-osx.cocoa.SelfInit check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn about improper use of '[super dealloc]' in Objective-C.

The clang-analyzer-osx.cocoa.SuperDealloc check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn about private ivars that are never used.

The clang-analyzer-osx.cocoa.UnusedIvars check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for passing non-Objective-C types to variadic collection initialization methods that expect only Objective-C types.

The clang-analyzer-osx.cocoa.VariadicMethodTypes check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check usage of CFErrorRef* parameters.

The clang-analyzer-osx.coreFoundation.CFError check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for proper uses of CFNumber APIs.

The clang-analyzer-osx.coreFoundation.CFNumber check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for null arguments to CFRetain/CFRelease/CFMakeCollectable.

The clang-analyzer-osx.coreFoundation.CFRetainRelease check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Checks for index out-of-bounds when using 'CFArray' API.

The clang-analyzer-osx.coreFoundation.containers.OutOfBounds check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warns if 'CFArray', 'CFDictionary', 'CFSet' are created with non-pointer-size values.

The clang-analyzer-osx.coreFoundation.containers.PointerSizedValues check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on using a floating point value as a loop counter (CERT: FLP30-C, FLP30-CPP).

The clang-analyzer-security.FloatLoopCounter check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Finds calls to the function 'putenv' which pass a pointer to an automatic (stack-allocated) array as the argument.

The clang-analyzer-security.PutenvStackArray check is an alias of Clang Static Analyzer security.PutenvStackArray.

Warn on possible reversed order of 'setgid(getgid()))' and 'setuid(getuid())' (CERT: POS36-C).

The clang-analyzer-security.SetgidSetuidOrder check is an alias of Clang Static Analyzer security.SetgidSetuidOrder.

Finds usages of possibly invalidated pointers.

The clang-analyzer-security.cert.env.InvalidPtr check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of unsecure or deprecated buffer manipulating functions.

The clang-analyzer-security.insecureAPI.DeprecatedOrUnsafeBufferHandling check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of functions whose return values must be always checked.

The clang-analyzer-security.insecureAPI.UncheckedReturn check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the 'bcmp' function.

The clang-analyzer-security.insecureAPI.bcmp check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the 'bcopy' function.

The clang-analyzer-security.insecureAPI.bcopy check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the 'bzero' function.

The clang-analyzer-security.insecureAPI.bzero check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the '-decodeValueOfObjCType:at:' method.

The clang-analyzer-security.insecureAPI.decodeValueOfObjCType check is an alias of Clang Static Analyzer security.insecureAPI.decodeValueOfObjCType.

Warn on uses of the 'getpw' function.

The clang-analyzer-security.insecureAPI.getpw check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the 'gets' function.

The clang-analyzer-security.insecureAPI.gets check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn when 'mkstemp' is passed fewer than 6 X's in the format string.

The clang-analyzer-security.insecureAPI.mkstemp check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the 'mktemp' function.

The clang-analyzer-security.insecureAPI.mktemp check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the 'rand', 'random', and related functions.

The clang-analyzer-security.insecureAPI.rand check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the 'strcpy' and 'strcat' functions.

The clang-analyzer-security.insecureAPI.strcpy check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Warn on uses of the 'vfork' function.

The clang-analyzer-security.insecureAPI.vfork check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check calls to various UNIX/Posix functions.

The clang-analyzer-unix.API check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for calls to blocking functions inside a critical section.

The clang-analyzer-unix.BlockInCriticalSection check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for improper use of 'errno'.

The clang-analyzer-unix.Errno check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for memory leaks, double free, and use-after-free problems. Traces memory managed by malloc()/free().

The clang-analyzer-unix.Malloc check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for dubious malloc arguments involving sizeof.

The clang-analyzer-unix.MallocSizeof check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for mismatched deallocators.

The clang-analyzer-unix.MismatchedDeallocator check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for invalid arguments of C standard library functions, and apply relations between arguments and return value.

The clang-analyzer-unix.StdCLibraryFunctions check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check stream handling functions.

The clang-analyzer-unix.Stream check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for proper usage of vfork.

The clang-analyzer-unix.Vfork check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check the size argument passed into C string functions for common erroneous patterns.

The clang-analyzer-unix.cstring.BadSizeArg check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for null pointers being passed as arguments to C string functions.

The clang-analyzer-unix.cstring.NullArg check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for va_lists which are copied onto itself.

The clang-analyzer-valist.CopyToSelf check is an alias of Clang Static Analyzer valist.CopyToSelf.

Check for usages of uninitialized (or already released) va_lists.

The clang-analyzer-valist.Uninitialized check is an alias of Clang Static Analyzer valist.Uninitialized.

Check for va_lists which are not released by a va_end call.

The clang-analyzer-valist.Unterminated check is an alias of Clang Static Analyzer valist.Unterminated.

Check for no uncounted member variables.

The clang-analyzer-webkit.NoUncountedMemberChecker check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check for any ref-countable base class having virtual destructor.

The clang-analyzer-webkit.RefCntblBaseVirtualDtor check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Check uncounted lambda captures.

The clang-analyzer-webkit.UncountedLambdaCapturesChecker check is an alias, please see Clang Static Analyzer Available Checkers for more information.

Checks for some thread-unsafe functions against a black list of known-to-be-unsafe functions. Usually they access static variables without synchronization (e.g. gmtime(3)) or utilize signals in a racy way. The set of functions to check is specified with the FunctionSet option.

Note that using some thread-unsafe functions may be still valid in concurrent programming if only a single thread is used (e.g. setenv(3)), however, some functions may track a state in global variables which would be clobbered by subsequent (non-parallel, but concurrent) calls to a related function. E.g. the following code suffers from unprotected accesses to a global state:

// getnetent(3) maintains global state with DB connection, etc.
// If a concurrent green thread calls getnetent(3), the global state is corrupted.
netent = getnetent();
yield();
netent = getnetent();

Examples:

tm = gmtime(timep); // uses a global buffer

sleep(1); // implementation may use SIGALRM

FunctionSet

Specifies which functions in libc should be considered thread-safe, possible values are posix, glibc, or any.

posix means POSIX defined thread-unsafe functions. POSIX.1-2001 in "2.9.1 Thread-Safety" defines that all functions specified in the standard are thread-safe except a predefined list of thread-unsafe functions.

Glibc defines some of them as thread-safe (e.g. dirname(3)), but adds non-POSIX thread-unsafe ones (e.g. getopt_long(3)). Glibc's list is compiled from GNU web documentation with a search for MT-Safe tag: https://www.gnu.org/software/libc/manual/html_node/POSIX-Safety-Concepts.html

If you want to identify thread-unsafe API for at least one libc or unsure which libc will be used, use any (default).

Finds pthread_setcanceltype function calls where a thread's cancellation type is set to asynchronous. Asynchronous cancellation type (PTHREAD_CANCEL_ASYNCHRONOUS) is generally unsafe, use type PTHREAD_CANCEL_DEFERRED instead which is the default. Even with deferred cancellation, a cancellation point in an asynchronous signal handler may still be acted upon and the effect is as if it was an asynchronous cancellation.

pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &oldtype);

This check corresponds to the CERT C Coding Standard rule POS47-C. Do not use threads that can be canceled asynchronously.

cert-pos47-c redirects here as an alias of this check.

The cppcoreguidelines-avoid-c-arrays check is an alias, please see modernize-avoid-c-arrays for more information.

Flags C++20 coroutine lambdas with non-empty capture lists that may cause use-after-free errors and suggests avoiding captures or ensuring the lambda closure object has a guaranteed lifetime.

This check implements CP.51 from the C++ Core Guidelines.

Using coroutine lambdas with non-empty capture lists can be risky, as capturing variables can lead to accessing freed memory after the first suspension point. This issue can occur even with refcounted smart pointers and copyable types. When a lambda expression creates a coroutine, it results in a closure object with storage, which is often on the stack and will eventually go out of scope. When the closure object goes out of scope, its captures also go out of scope. While normal lambdas finish executing before this happens, coroutine lambdas may resume from suspension after the closure object has been destructed, resulting in use-after-free memory access for all captures.

Consider the following example:

int value = get_value();
std::shared_ptr<Foo> sharedFoo = get_foo();
{
    const auto lambda = [value, sharedFoo]() -> std::future<void>
    {
        co_await something();
        // "sharedFoo" and "value" have already been destroyed
        // the "shared" pointer didn't accomplish anything
    };
    lambda();
} // the lambda closure object has now gone out of scope

In this example, the lambda object is defined with two captures: value and sharedFoo. When lambda() is called, the lambda object is created on the stack, and the captures are copied into the closure object. When the coroutine is suspended, the lambda object goes out of scope, and the closure object is destroyed. When the coroutine is resumed, the captured variables may have been destroyed, resulting in use-after-free bugs.

In conclusion, the use of coroutine lambdas with non-empty capture lists can lead to use-after-free errors when resuming the coroutine after the closure object has been destroyed. This check helps prevent such errors by flagging C++20 coroutine lambdas with non-empty capture lists and suggesting avoiding captures or ensuring the lambda closure object has a guaranteed lifetime.

Following these guidelines can help ensure the safe and reliable use of coroutine lambdas in C++ code.

This check warns when structs or classes that are copyable or movable, and have const-qualified or reference (lvalue or rvalue) data members. Having such members is rarely useful, and makes the class only copy-constructible but not copy-assignable.

Examples:

// Bad, const-qualified member
struct Const {
  const int x;
}

// Good:
class Foo {
 public:
  int get() const { return x; }
 private:
  int x;
};

// Bad, lvalue reference member
struct Ref {
  int& x;
};

// Good:
struct Foo {
  int* x;
  std::unique_ptr<int> x;
  std::shared_ptr<int> x;
  gsl::not_null<int*> x;
};

// Bad, rvalue reference member
struct RefRef {
  int&& x;
};

This check implements C.12 from the C++ Core Guidelines.

Further reading: Data members: Never const.

Warns when using do-while loops. They are less readable than plain while loops, since the termination condition is at the end and the condition is not checked prior to the first iteration. This can lead to subtle bugs.

This check implements ES.75 from the C++ Core Guidelines.

Examples:

int x;
do {
    std::cin >> x;
    // ...
} while (x < 0);

IgnoreMacros

Ignore the check when analyzing macros. This is useful for safely defining function-like macros:

#define FOO_BAR(x) \
do { \
  foo(x); \
  bar(x); \
} while(0)

Defaults to false.

The usage of goto for control flow is error prone and should be replaced with looping constructs. Only forward jumps in nested loops are accepted.

This check implements ES.76 from the C++ Core Guidelines and 6.3.1 from High Integrity C++ Coding Standard.

For more information on why to avoid programming with goto you can read the famous paper A Case against the GO TO Statement..

The check diagnoses goto for backward jumps in every language mode. These should be replaced with C/C++ looping constructs.

// Bad, handwritten for loop.
int i = 0;
// Jump label for the loop
loop_start:
do_some_operation();

if (i < 100) {
  ++i;
  goto loop_start;
}

// Better
for(int i = 0; i < 100; ++i)
  do_some_operation();

Modern C++ needs goto only to jump out of nested loops.

for(int i = 0; i < 100; ++i) {
  for(int j = 0; j < 100; ++j) {
    if (i * j > 500)
      goto early_exit;
  }
}

early_exit:
some_operation();

All other uses of goto are diagnosed in C++.

The cppcoreguidelines-avoid-magic-numbers check is an alias, please see readability-magic-numbers for more information.

Finds non-const global variables as described in I.2 of C++ Core Guidelines. As R.6 of C++ Core Guidelines is a duplicate of rule I.2 it also covers that rule.

char a;  // Warns!
const char b =  0;

namespace some_namespace
{
    char c;  // Warns!
    const char d = 0;
}

char * c_ptr1 = &some_namespace::c;  // Warns!
char *const c_const_ptr = &some_namespace::c;  // Warns!
char & c_reference = some_namespace::c;  // Warns!

class Foo  // No Warnings inside Foo, only namespace scope is covered
{
public:
    char e = 0;
    const char f = 0;
protected:
    char g = 0;
private:
    char h = 0;
};

The variables a, c, c_ptr1, c_const_ptr and c_reference will all generate warnings since they are either a non-const globally accessible variable, a pointer or a reference providing global access to non-const data or both.

AllowInternalLinkage

When set to true, static non-const variables and variables in anonymous namespaces will not generate a warning. The default value is false.

Warns when a coroutine accepts reference parameters. After a coroutine suspend point, references could be dangling and no longer valid. Instead, pass parameters as values.

Examples:

std::future<int> someCoroutine(int& val) {
  co_await ...;
  // When the coroutine is resumed, 'val' might no longer be valid.
  if (val) ...
}

This check implements CP.53 from the C++ Core Guidelines.

The cppcoreguidelines-c-copy-assignment-signature check is an alias, please see misc-unconventional-assign-operator for more information.

The cppcoreguidelines-explicit-virtual-functions check is an alias, please see modernize-use-override for more information.

Checks whether there are local variables that are declared without an initial value. These may lead to unexpected behavior if there is a code path that reads the variable before assigning to it.

This rule is part of the Type safety (Type.5) profile and ES.20 from the C++ Core Guidelines.

Only integers, booleans, floats, doubles and pointers are checked. The fix option initializes all detected values with the value of zero. An exception is float and double types, which are initialized to NaN.

As an example a function that looks like this:

void function() {
  int x;
  char *txt;
  double d;

  // Rest of the function.
}

Would be rewritten to look like this:

#include <math.h>

void function() {
  int x = 0;
  char *txt = nullptr;
  double d = NAN;

  // Rest of the function.
}

It warns for the uninitialized enum case, but without a FixIt:

enum A {A1, A2, A3};
enum A_c : char { A_c1, A_c2, A_c3 };
enum class B { B1, B2, B3 };
enum class B_i : int { B_i1, B_i2, B_i3 };
void function() {
  A a;     // Warning: variable 'a' is not initialized
  A_c a_c; // Warning: variable 'a_c' is not initialized
  B b;     // Warning: variable 'b' is not initialized
  B_i b_i; // Warning: variable 'b_i' is not initialized
}

IncludeStyle

A string specifying which include-style is used, llvm or google. Default is llvm.

MathHeader

A string specifying the header to include to get the definition of NAN. Default is <math.h>.

This check flags initializers of globals that access extern objects, and therefore can lead to order-of-initialization problems.

This check implements I.22 from the C++ Core Guidelines.

Note that currently this does not flag calls to non-constexpr functions, and therefore globals could still be accessed from functions themselves.

The cppcoreguidelines-macro-to-enum check is an alias, please see modernize-macro-to-enum for more information.

Finds macro usage that is considered problematic because better language constructs exist for the task.

The relevant sections in the C++ Core Guidelines are ES.31, and ES.32.

Examples:

#define C 0
#define F1(x, y) ((a) > (b) ? (a) : (b))
#define F2(...) (__VA_ARGS__)
#define F3(x, y) x##y
#define COMMA ,
#define NORETURN [[noreturn]]
#define DEPRECATED attribute((deprecated))
#if LIB_EXPORTS
#define DLLEXPORTS __declspec(dllexport)
#else
#define DLLEXPORTS __declspec(dllimport)
#endif

results in the following warnings:

4 warnings generated.
test.cpp:1:9: warning: macro 'C' used to declare a constant; consider using a 'constexpr' constant [cppcoreguidelines-macro-usage]
#define C 0
        ^
test.cpp:2:9: warning: function-like macro 'F1' used; consider a 'constexpr' template function [cppcoreguidelines-macro-usage]
#define F1(x, y) ((a) > (b) ? (a) : (b))
        ^
test.cpp:3:9: warning: variadic macro 'F2' used; consider using a 'constexpr' variadic template function [cppcoreguidelines-macro-usage]
#define F2(...) (__VA_ARGS__)
        ^

AllowedRegexp

A regular expression to filter allowed macros. For example DEBUG*|LIBTORRENT*|TORRENT*|UNI* could be applied to filter libtorrent. Default value is ^DEBUG_*.

CheckCapsOnly

Boolean flag to warn on all macros except those with CAPS_ONLY names. This option is intended to ease introduction of this check into older code bases. Default value is false.

IgnoreCommandLineMacros

Boolean flag to toggle ignoring command-line-defined macros. Default value is true.

Warns when lambda specify a by-value capture default and capture this.

By-value capture defaults in member functions can be misleading about whether data members are captured by value or reference. This occurs because specifying the capture default [=] actually captures the this pointer by value, not the data members themselves. As a result, data members are still indirectly accessed via the captured this pointer, which essentially means they are being accessed by reference. Therefore, even when using [=], data members are effectively captured by reference, which might not align with the user's expectations.

Examples:

struct AClass {
  int member;
  void misleadingLogic() {
    int local = 0;
    member = 0;
    auto f = [=]() mutable {
      local += 1;
      member += 1;
    };
    f();
    // Here, local is 0 but member is 1
  }

  void clearLogic() {
    int local = 0;
    member = 0;
    auto f = [this, local]() mutable {
      local += 1;
      member += 1;
    };
    f();
    // Here, local is 0 but member is 1
  }
};

This check implements F.54 from the C++ Core Guidelines.

Warns when a forwarding reference parameter is not forwarded inside the function body.

Example:

template <class T>
void wrapper(T&& t) {
  impl(std::forward<T>(t), 1, 2); // Correct
}

template <class T>
void wrapper2(T&& t) {
  impl(t, 1, 2); // Oops - should use std::forward<T>(t)
}

template <class T>
void wrapper3(T&& t) {
  impl(std::move(t), 1, 2); // Also buggy - should use std::forward<T>(t)
}

template <class F>
void wrapper_function(F&& f) {
  std::forward<F>(f)(1, 2); // Correct
}

template <class F>
void wrapper_function2(F&& f) {
  f(1, 2); // Incorrect - may not invoke the desired qualified function operator
}

This check implements F.19 from the C++ Core Guidelines.

Checks for silent narrowing conversions, e.g: int i = 0; i += 0.1;. While the issue is obvious in this former example, it might not be so in the following: void MyClass::f(double d) { int_member_ += d; }.

This check implements ES.46 from the C++ Core Guidelines.

We enforce only part of the guideline, more specifically, we flag narrowing conversions from:

• an integer to a narrower integer (e.g. char to unsigned char) if WarnOnIntegerNarrowingConversion Option is set,
• an integer to a narrower floating-point (e.g. uint64_t to float) if WarnOnIntegerToFloatingPointNarrowingConversion Option is set,
• a floating-point to an integer (e.g. double to int),
• a floating-point to a narrower floating-point (e.g. double to float) if WarnOnFloatingPointNarrowingConversion Option is set.

This check will flag:

• All narrowing conversions that are not marked by an explicit cast (c-style or static_cast). For example: int i = 0; i += 0.1;, void f(int); f(0.1);,
• All applications of binary operators with a narrowing conversions. For example: int i; i+= 0.1;.

WarnOnIntegerNarrowingConversion

When true, the check will warn on narrowing integer conversion (e.g. int to size_t). true by default.

WarnOnIntegerToFloatingPointNarrowingConversion

When true, the check will warn on narrowing integer to floating-point conversion (e.g. size_t to double). true by default.

WarnOnFloatingPointNarrowingConversion

When true, the check will warn on narrowing floating point conversion (e.g. double to float). true by default.

WarnWithinTemplateInstantiation

When true, the check will warn on narrowing conversions within template instantiations. false by default.

WarnOnEquivalentBitWidth

When true, the check will warn on narrowing conversions that arise from casting between types of equivalent bit width. (e.g. int n = uint(0); or long long n = double(0);) true by default.

IgnoreConversionFromTypes

Narrowing conversions from any type in this semicolon-separated list will be ignored. This may be useful to weed out commonly occurring, but less commonly problematic assignments such as int n = std::vector<char>().size(); or int n = std::difference(it1, it2);. The default list is empty, but one suggested list for a legacy codebase would be size_t;ptrdiff_t;size_type;difference_type.

PedanticMode

When true, the check will warn on assigning a floating point constant to an integer value even if the floating point value is exactly representable in the destination type (e.g. int i = 1.0;). false by default.

• What does "narrowing conversion from 'int' to 'float'" mean?

An IEEE754 Floating Point number can represent all integer values in the range [-2^PrecisionBits, 2^PrecisionBits] where PrecisionBits is the number of bits in the mantissa.

For float this would be [-2^23, 2^23], where int can represent values in the range [-2^31, 2^31-1].

• What does "implementation-defined" mean?

You may have encountered messages like "narrowing conversion from 'unsigned int' to signed type 'int' is implementation-defined". The C/C++ standard does not mandate two's complement for signed integers, and so the compiler is free to define what the semantics are for converting an unsigned integer to signed integer. Clang's implementation uses the two's complement format.

This check handles C-Style memory management using malloc(), realloc(), calloc() and free(). It warns about its use and tries to suggest the use of an appropriate RAII object. Furthermore, it can be configured to check against a user-specified list of functions that are used for memory management (e.g. posix_memalign()).

This check implements R.10 from the C++ Core Guidelines.

There is no attempt made to provide fix-it hints, since manual resource management isn't easily transformed automatically into RAII.

// Warns each of the following lines.
// Containers like std::vector or std::string should be used.
char* some_string = (char*) malloc(sizeof(char) * 20);
char* some_string = (char*) realloc(sizeof(char) * 30);
free(some_string);

int* int_array = (int*) calloc(30, sizeof(int));

// Rather use a smartpointer or stack variable.
struct some_struct* s = (struct some_struct*) malloc(sizeof(struct some_struct));

Allocations

Semicolon-separated list of fully qualified names of memory allocation functions. Defaults to ::malloc;::calloc.

Deallocations

Semicolon-separated list of fully qualified names of memory allocation functions. Defaults to ::free.

Reallocations

Semicolon-separated list of fully qualified names of memory allocation functions. Defaults to ::realloc.

Flags coroutines that suspend while a lock guard is in scope at the suspension point.

When a coroutine suspends, any mutexes held by the coroutine will remain locked until the coroutine resumes and eventually destructs the lock guard. This can lead to long periods with a mutex held and runs the risk of deadlock.

Instead, locks should be released before suspending a coroutine.

This check only checks suspending coroutines while a lock_guard is in scope; it does not consider manual locking or unlocking of mutexes, e.g., through calls to std::mutex::lock().

Examples:

future bad_coro() {
  std::lock_guard lock{mtx};
  ++some_counter;
  co_await something(); // Suspending while holding a mutex
}

future good_coro() {
  {
    std::lock_guard lock{mtx};
    ++some_counter;
  }
  // Destroy the lock_guard to release the mutex before suspending the coroutine
  co_await something(); // Suspending while holding a mutex
}

This check implements CP.52 from the C++ Core Guidelines.

This check implements C.37 from the C++ Core Guidelines.

The cppcoreguidelines-noexcept-destructor check is an alias, please see performance-noexcept-destructor for more information.

This check implements C.66 from the C++ Core Guidelines.

The cppcoreguidelines-noexcept-move-operations check is an alias, please see performance-noexcept-move-constructor for more information.

This check implements C.83 , C.84 and C.85 from the C++ Core Guidelines.

The cppcoreguidelines-noexcept-swap check is an alias, please see performance-noexcept-swap for more information.

The cppcoreguidelines-non-private-member-variables-in-classes check is an alias, please see misc-non-private-member-variables-in-classes for more information.

This check implements the type-based semantics of gsl::owner<T*>, which allows static analysis on code, that uses raw pointers to handle resources like dynamic memory, but won't introduce RAII concepts.

This check implements I.11, C.33, R.3 and GSL.Views from the C++ Core Guidelines. The definition of a gsl::owner<T*> is straight forward

namespace gsl { template <typename T> owner = T; }

It is therefore simple to introduce the owner even without using an implementation of the Guideline Support Library.

All checks are purely type based and not (yet) flow sensitive.

The following examples will demonstrate the correct and incorrect initializations of owners, assignment is handled the same way. Note that both new and malloc()-like resource functions are considered to produce resources.

// Creating an owner with factory functions is checked.
gsl::owner<int*> function_that_returns_owner() { return gsl::owner<int*>(new int(42)); }

// Dynamic memory must be assigned to an owner
int* Something = new int(42); // BAD, will be caught
gsl::owner<int*> Owner = new int(42); // Good
gsl::owner<int*> Owner = new int[42]; // Good as well

// Returned owner must be assigned to an owner
int* Something = function_that_returns_owner(); // Bad, factory function
gsl::owner<int*> Owner = function_that_returns_owner(); // Good, result lands in owner

// Something not a resource or owner should not be assigned to owners
int Stack = 42;
gsl::owner<int*> Owned = &Stack; // Bad, not a resource assigned

In the case of dynamic memory as resource, only gsl::owner<T*> variables are allowed to be deleted.

// Example Bad, non-owner as resource handle, will be caught.
int* NonOwner = new int(42); // First warning here, since new must land in an owner
delete NonOwner; // Second warning here, since only owners are allowed to be deleted

// Example Good, Ownership correctly stated
gsl::owner<int*> Owner = new int(42); // Good
delete Owner; // Good as well, statically enforced, that only owners get deleted

The check will furthermore ensure, that functions, that expect a gsl::owner<T*> as argument get called with either a gsl::owner<T*> or a newly created resource.

void expects_owner(gsl::owner<int*> o) { delete o; }

// Bad Code
int NonOwner = 42;
expects_owner(&NonOwner); // Bad, will get caught

// Good Code
gsl::owner<int*> Owner = new int(42);
expects_owner(Owner); // Good
expects_owner(new int(42)); // Good as well, recognized created resource

// Port legacy code for better resource-safety
gsl::owner<FILE*> File = fopen("my_file.txt", "rw+");
FILE* BadFile = fopen("another_file.txt", "w"); // Bad, warned

// ... use the file

fclose(File); // Ok, File is annotated as 'owner<>'
fclose(BadFile); // BadFile is not an 'owner<>', will be warned

LegacyResourceProducers

Semicolon-separated list of fully qualified names of legacy functions that create resources but cannot introduce gsl::owner<>. Defaults to ::malloc;::aligned_alloc;::realloc;::calloc;::fopen;::freopen;::tmpfile.

LegacyResourceConsumers

Semicolon-separated list of fully qualified names of legacy functions expecting resource owners as pointer arguments but cannot introduce gsl::owner<>. Defaults to ::free;::realloc;::freopen;::fclose.

Using gsl::owner<T*> in a typedef or alias is not handled correctly.

using heap_int = gsl::owner<int*>;
heap_int allocated = new int(42); // False positive!

The gsl::owner<T*> is declared as a templated type alias. In template functions and classes, like in the example below, the information of the type aliases gets lost. Therefore using gsl::owner<T*> in a heavy templated code base might lead to false positives.

Known code constructs that do not get diagnosed correctly are:

• std::exchange

• std::vector<gsl::owner<T*>>

  // This template function works as expected. Type information doesn't get lost.
  template <typename T>
  void delete_owner(gsl::owner<T*> owned_object) {
    delete owned_object; // Everything alright
  }
  
  gsl::owner<int*> function_that_returns_owner() { return gsl::owner<int*>(new int(42)); }
  
  // Type deduction does not work for auto variables.
  // This is caught by the check and will be noted accordingly.
  auto OwnedObject = function_that_returns_owner(); // Type of OwnedObject will be int*
  
  // Problematic function template that looses the typeinformation on owner
  template <typename T>
  void bad_template_function(T some_object) {
    // This line will trigger the warning, that a non-owner is assigned to an owner
    gsl::owner<T*> new_owner = some_object;
  }
  
  // Calling the function with an owner still yields a false positive.
  bad_template_function(gsl::owner<int*>(new int(42)));
  
  
  // The same issue occurs with templated classes like the following.
  template <typename T>
  class OwnedValue {
  public:
    const T getValue() const { return _val; }
  private:
    T _val;
  };
  
  // Code, that yields a false positive.
  OwnedValue<gsl::owner<int*>> Owner(new int(42)); // Type deduction yield T -> int *
  // False positive, getValue returns int* and not gsl::owner<int*>
  gsl::owner<int*> OwnedInt = Owner.getValue();

Another limitation of the current implementation is only the type based checking. Suppose you have code like the following:

// Two owners with assigned resources
gsl::owner<int*> Owner1 = new int(42);
gsl::owner<int*> Owner2 = new int(42);

Owner2 = Owner1; // Conceptual Leak of initial resource of Owner2!
Owner1 = nullptr;

The semantic of a gsl::owner<T*> is mostly like a std::unique_ptr<T>, therefore assignment of two gsl::owner<T*> is considered a move, which requires that the resource Owner2 must have been released before the assignment. This kind of condition could be caught in later improvements of this check with flowsensitive analysis. Currently, the Clang Static Analyzer catches this bug for dynamic memory, but not for general types of resources.

Finds member initializations in the constructor body which can be  converted into member initializers of the constructor instead. This not only improves the readability of the code but also positively affects its performance. Class-member assignments inside a control statement or following the first control statement are ignored.

This check implements C.49 from the C++ Core Guidelines.

Please note, that this check does not enforce rule C.48 from the C++ Core Guidelines. For that purpose see check modernize-use-default-member-init.

class C {
  int n;
  int m;
public:
  C() {
    n = 1; // Literal in default constructor
    if (dice())
      return;
    m = 1;
  }
};

Here n can be initialized in the constructor initializer list, unlike m, as m's initialization follows a control statement (if):

class C {
  int n;
  int m;
public:
  C(): n(1) {
    if (dice())
      return;
    m = 1;
  }
};

class C {
  int n;
  int m;
public:
  C(int nn, int mm) {
    n = nn; // Neither default constructor nor literal
    if (dice())
      return;
    m = mm;
  }
};

Here n can be initialized in the constructor initializer list, unlike m, as m's initialization follows a control statement (if):

C(int nn, int mm) : n(nn) {
  if (dice())
    return;
  m = mm;
}

This check flags all array to pointer decays.

Pointers should not be used as arrays. span<T> is a bounds-checked, safe alternative to using pointers to access arrays.

This rule is part of the Bounds safety (Bounds 3) profile from the C++ Core Guidelines.

This check flags all array subscript expressions on static arrays and std::arrays that either do not have a constant integer expression index or are out of bounds (for std::array). For out-of-bounds checking of static arrays, see the -Warray-bounds Clang diagnostic.

This rule is part of the Bounds safety (Bounds 2) profile from the C++ Core Guidelines.

Optionally, this check can generate fixes using gsl::at for indexing.

GslHeader

The check can generate fixes after this option has been set to the name of the include file that contains gsl::at(), e.g. "gsl/gsl.h".

IncludeStyle

A string specifying which include-style is used, llvm or google. Default is llvm.

This check flags all usage of pointer arithmetic, because it could lead to an invalid pointer. Subtraction of two pointers is not flagged by this check.

Pointers should only refer to single objects, and pointer arithmetic is fragile and easy to get wrong. span<T> is a bounds-checked, safe type for accessing arrays of data.

This rule is part of the Bounds safety (Bounds 1) profile from the C++ Core Guidelines.

Imposes limitations on the use of const_cast within C++ code. It depends on the StrictMode option setting to determine whether it should flag all instances of const_cast or only those that remove either const or volatile qualifier.

Modifying a variable that has been declared as const in C++ is generally considered undefined behavior, and this remains true even when using const_cast. In C++, the const qualifier indicates that a variable is intended to be read-only, and the compiler enforces this by disallowing any attempts to change the value of that variable.

Removing the volatile qualifier in C++ can have serious consequences. This qualifier indicates that a variable's value can change unpredictably, and removing it may lead to undefined behavior, optimization problems, and debugging challenges. It's essential to retain the volatile qualifier in situations where the variable's volatility is a crucial aspect of program correctness and reliability.

This rule is part of the Type safety (Type 3) profile and ES.50: Don’t cast away const rule from the C++ Core Guidelines.

StrictMode

When this setting is set to true, it means that any usage of const_cast is not allowed. On the other hand, when it's set to false, it permits casting to const or volatile types. Default value is false.

This check flags all use of C-style casts that perform a static_cast downcast, const_cast, or reinterpret_cast.

Use of these casts can violate type safety and cause the program to access a variable that is actually of type X to be accessed as if it were of an unrelated type Z. Note that a C-style (T)expression cast means to perform the first of the following that is possible: a const_cast, a static_cast, a static_cast followed by a const_cast, a reinterpret_cast, or a reinterpret_cast followed by a const_cast. This rule bans (T)expression only when used to perform an unsafe cast.

This rule is part of the Type safety (Type.4) profile from the C++ Core Guidelines.

The check flags user-provided constructor definitions that do not initialize all fields that would be left in an undefined state by default construction, e.g. builtins, pointers and record types without user-provided default constructors containing at least one such type. If these fields aren't initialized, the constructor will leave some of the memory in an undefined state.

For C++11 it suggests fixes to add in-class field initializers. For older versions it inserts the field initializers into the constructor initializer list. It will also initialize any direct base classes that need to be zeroed in the constructor initializer list.

The check takes assignment of fields in the constructor body into account but generates false positives for fields initialized in methods invoked in the constructor body.

The check also flags variables with automatic storage duration that have record types without a user-provided constructor and are not initialized. The suggested fix is to zero initialize the variable via {} for C++11 and beyond or = {} for older language versions.

IgnoreArrays

If set to true, the check will not warn about array members that are not zero-initialized during construction. For performance critical code, it may be important to not initialize fixed-size array members. Default is false.

UseAssignment

If set to true, the check will provide fix-its with literal initializers ( int i = 0; ) instead of curly braces ( int i{}; ).

This rule is part of the Type safety (Type.6) profile from the C++ Core Guidelines.

This check flags all uses of reinterpret_cast in C++ code.

Use of these casts can violate type safety and cause the program to access a variable that is actually of type X to be accessed as if it were of an unrelated type Z.

This rule is part of the Type safety (Type.1.1) profile from the C++ Core Guidelines.

This check flags all usages of static_cast, where a base class is casted to a derived class. In those cases, a fix-it is provided to convert the cast to a dynamic_cast.

Use of these casts can violate type safety and cause the program to access a variable that is actually of type X to be accessed as if it were of an unrelated type Z.

This rule is part of the Type safety (Type.2) profile from the C++ Core Guidelines.

StrictMode

When set to false, no warnings are emitted for casts on non-polymorphic types. Default is true.

This check flags all access to members of unions. Passing unions as a whole is not flagged.

Reading from a union member assumes that member was the last one written, and writing to a union member assumes another member with a nontrivial destructor had its destructor called. This is fragile because it cannot generally be enforced to be safe in the language and so relies on programmer discipline to get it right.

This rule is part of the Type safety (Type.7) profile from the C++ Core Guidelines.

This check flags all calls to c-style vararg functions and all use of va_arg.

To allow for SFINAE use of vararg functions, a call is not flagged if a literal 0 is passed as the only vararg argument or function is used in unevaluated context.

Passing to varargs assumes the correct type will be read. This is fragile because it cannot generally be enforced to be safe in the language and so relies on programmer discipline to get it right.

This rule is part of the Type safety (Type.8) profile from the C++ Core Guidelines.

Warns when an rvalue reference function parameter is never moved within the function body.

Rvalue reference parameters indicate a parameter that should be moved with std::move from within the function body. Any such parameter that is never moved is confusing and potentially indicative of a buggy program.

Example:

void logic(std::string&& Input) {
  std::string Copy(Input); // Oops - forgot to std::move
}

Note that parameters that are unused and marked as such will not be diagnosed.

Example:

void conditional_use([[maybe_unused]] std::string&& Input) {
  // No diagnostic here since Input is unused and marked as such
}

AllowPartialMove

If set to true, the check accepts std::move calls containing any subexpression containing the parameter. CppCoreGuideline F.18 officially mandates that the parameter itself must be moved. Default is false.

// 'p' is flagged by this check if and only if AllowPartialMove is false
void move_members_of(pair<Obj, Obj>&& p) {
  pair<Obj, Obj> other;
  other.first = std::move(p.first);
  other.second = std::move(p.second);
}

// 'p' is never flagged by this check
void move_whole_pair(pair<Obj, Obj>&& p) {
  pair<Obj, Obj> other = std::move(p);
}

IgnoreUnnamedParams

If set to true, the check ignores unnamed rvalue reference parameters. Default is false.

IgnoreNonDeducedTemplateTypes

If set to true, the check ignores non-deduced template type rvalue reference parameters. Default is false.

template <class T>
struct SomeClass {
  // Below, 'T' is not deduced and 'T&&' is an rvalue reference type.
  // This will be flagged if and only if IgnoreNonDeducedTemplateTypes is
  // false. One suggested fix would be to specialize the class for 'T' and
  // 'T&' separately (e.g., see std::future), or allow only one of 'T' or
  // 'T&' instantiations of SomeClass (e.g., see std::optional).
  SomeClass(T&& t) { }
};

// Never flagged, since 'T' is a forwarding reference in a deduced context
template <class T>
void forwarding_ref(T&& t) {
  T other = std::forward<T>(t);
}

This check implements F.18 from the C++ Core Guidelines.

Flags slicing of member variables or vtable. Slicing happens when copying a derived object into a base object: the members of the derived object (both member variables and virtual member functions) will be discarded. This can be misleading especially for member function slicing, for example:

struct B { int a; virtual int f(); };
struct D : B { int b; int f() override; };

void use(B b) {  // Missing reference, intended?
  b.f();  // Calls B::f.
}

D d;
use(d);  // Slice.

This check implements ES.63 and C.145 from the C++ Core Guidelines.

The check finds classes where some but not all of the special member functions are defined.

By default the compiler defines a copy constructor, copy assignment operator, move constructor, move assignment operator and destructor. The default can be suppressed by explicit user-definitions. The relationship between which functions will be suppressed by definitions of other functions is complicated and it is advised that all five are defaulted or explicitly defined.

Note that defining a function with = delete is considered to be a definition.

This check implements C.21 from the C++ Core Guidelines.

AllowSoleDefaultDtor

When set to true (default is false), this check will only trigger on destructors if they are defined and not defaulted.

struct A { // This is fine.
  virtual ~A() = default;
};

struct B { // This is not fine.
  ~B() {}
};

struct C {
  // This is not checked, because the destructor might be defaulted in
  // another translation unit.
  ~C();
};

AllowMissingMoveFunctions

When set to true (default is false), this check doesn't flag classes which define no move operations at all. It still flags classes which define only one of either move constructor or move assignment operator. With this option enabled, the following class won't be flagged:

struct A {
  A(const A&);
  A& operator=(const A&);
  ~A();
};

AllowMissingMoveFunctionsWhenCopyIsDeleted

When set to true (default is false), this check doesn't flag classes which define deleted copy operations but don't define move operations. This flag is related to Google C++ Style Guide Copyable and Movable Types. With this option enabled, the following class won't be flagged:

struct A {
  A(const A&) = delete;
  A& operator=(const A&) = delete;
  ~A();
};

AllowImplicitlyDeletedCopyOrMove

When set to true (default is false), this check doesn't flag classes which implicitly delete copy or move operations. With this option enabled, the following class won't be flagged:

struct A : boost::noncopyable {
  ~A() { std::cout << "dtor\n"; }
};

This check implements C.48 from the C++ Core Guidelines.

The cppcoreguidelines-use-default-member-init check is an alias, please see modernize-use-default-member-init for more information.

Finds virtual classes whose destructor is neither public and virtual nor protected and non-virtual. A virtual class's destructor should be specified in one of these ways to prevent undefined behavior.

This check implements C.35 from the C++ Core Guidelines.

Note that this check will diagnose a class with a virtual method regardless of whether the class is used as a base class or not.

Fixes are available for user-declared and implicit destructors that are either public and non-virtual or protected and virtual. No fixes are offered for private destructors. There, the decision whether to make them private and virtual or protected and non-virtual depends on the use case and is thus left to the user.

For example, the following classes/structs get flagged by the check since they violate guideline C.35:

struct Foo {        // NOK, protected destructor should not be virtual
  virtual void f();
protected:
  virtual ~Foo(){}
};

class Bar {         // NOK, public destructor should be virtual
  virtual void f();
public:
  ~Bar(){}
};

This would be rewritten to look like this:

struct Foo {        // OK, destructor is not virtual anymore
  virtual void f();
protected:
  ~Foo(){}
};

class Bar {         // OK, destructor is now virtual
  virtual void f();
public:
  virtual ~Bar(){}
};

Finds usages of OSSpinlock, which is deprecated due to potential livelock problems.

This check will detect following function invocations:

• OSSpinlockLock
• OSSpinlockTry
• OSSpinlockUnlock

The corresponding information about the problem of OSSpinlock: https://blog.postmates.com/why-spinlocks-are-bad-on-ios-b69fc5221058

Finds declarations of dispatch_once_t variables without static or global storage. The behavior of using dispatch_once_t predicates with automatic or dynamic storage is undefined by libdispatch, and should be avoided.

It is a common pattern to have functions initialize internal static or global data once when the function runs, but programmers have been known to miss the static on the dispatch_once_t predicate, leading to an uninitialized flag value at the mercy of the stack.

Programmers have also been known to make dispatch_once_t variables be members of structs or classes, with the intent to lazily perform some expensive struct or class member initialization only once; however, this violates the libdispatch requirements.

See the discussion section of Apple's dispatch_once documentation for more information.

Warns if a function or method is called with default arguments.

For example, given the declaration:

int foo(int value = 5) { return value; }

A function call expression that uses a default argument will be diagnosed. Calling it without defaults will not cause a warning:

foo();  // warning
foo(0); // no warning

See the features disallowed in Fuchsia at https://fuchsia.dev/fuchsia-src/development/languages/c-cpp/cxx?hl=en

Warns if a function or method is declared with default parameters.

For example, the declaration:

int foo(int value = 5) { return value; }

will cause a warning.

See the features disallowed in Fuchsia at https://fuchsia.dev/fuchsia-src/development/languages/c-cpp/cxx?hl=en

The fuchsia-header-anon-namespaces check is an alias, please see google-build-namespace for more information.

Warns if a class inherits from multiple classes that are not pure virtual.

For example, declaring a class that inherits from multiple concrete classes is disallowed:

class Base_A {
public:
  virtual int foo() { return 0; }
};

class Base_B {
public:
  virtual int bar() { return 0; }
};

// Warning
class Bad_Child1 : public Base_A, Base_B {};

A class that inherits from a pure virtual is allowed:

class Interface_A {
public:
  virtual int foo() = 0;
};

class Interface_B {
public:
  virtual int bar() = 0;
};

// No warning
class Good_Child1 : public Interface_A, Interface_B {
  virtual int foo() override { return 0; }
  virtual int bar() override { return 0; }
};

See the features disallowed in Fuchsia at https://fuchsia.dev/fuchsia-src/development/languages/c-cpp/cxx?hl=en

Warns if an operator is overloaded, except for the assignment (copy and move) operators.

For example:

int operator+(int);     // Warning

B &operator=(const B &Other);  // No warning
B &operator=(B &&Other) // No warning

See the features disallowed in Fuchsia at https://fuchsia.dev/fuchsia-src/development/languages/c-cpp/cxx?hl=en

Warns if global, non-trivial objects with static storage are constructed, unless the object is statically initialized with a constexpr constructor or has no explicit constructor.

For example:

class A {};

class B {
public:
  B(int Val) : Val(Val) {}
private:
  int Val;
};

class C {
public:
  constexpr C(int Val) : Val(Val) {}
  C(int Val1, int Val2) : Val(Val1+Val2) {}

private:
  int Val;
};

static A a;         // No warning, as there is no explicit constructor
static C c(0);      // No warning, as constructor is constexpr

static B b(0);      // Warning, as constructor is not constexpr
static C c2(0, 1);  // Warning, as constructor is not constexpr

static int i;       // No warning, as it is trivial

extern int get_i();
static C c3(get_i());// Warning, as the constructor is dynamically initialized

See the features disallowed in Fuchsia at https://fuchsia.dev/fuchsia-src/development/languages/c-cpp/cxx?hl=en

Functions that have trailing returns are disallowed, except for those using decltype specifiers and lambda with otherwise unutterable return types.

For example:

// No warning
int add_one(const int arg) { return arg; }

// Warning
auto get_add_one() -> int (*)(const int) {
  return add_one;
}

Exceptions are made for lambdas and decltype specifiers:

// No warning
auto lambda = [](double x, double y) -> double {return x + y;};

// No warning
template <typename T1, typename T2>
auto fn(const T1 &lhs, const T2 &rhs) -> decltype(lhs + rhs) {
  return lhs + rhs;
}

See the features disallowed in Fuchsia at https://fuchsia.dev/fuchsia-src/development/languages/c-cpp/cxx?hl=en

Warns if classes are defined with virtual inheritance.

For example, classes should not be defined with virtual inheritance:

class B : public virtual A {};   // warning

See the features disallowed in Fuchsia at https://fuchsia.dev/fuchsia-src/development/languages/c-cpp/cxx?hl=en

Check that make_pair's template arguments are deduced.

G++ 4.6 in C++11 mode fails badly if make_pair's template arguments are specified explicitly, and such use isn't intended in any case.

Corresponding cpplint.py check name: build/explicit_make_pair.

cert-dcl59-cpp redirects here as an alias for this check. fuchsia-header-anon-namespaces redirects here as an alias for this check.

Finds anonymous namespaces in headers.

https://google.github.io/styleguide/cppguide.html#Namespaces

Corresponding cpplint.py check name: build/namespaces.

Finds using namespace directives.

The check implements the following rule of the Google C++ Style Guide:

// Forbidden -- This pollutes the namespace.
using namespace foo;

Corresponding cpplint.py check name: build/namespaces.

Checks that default arguments are not given for virtual methods.

See https://google.github.io/styleguide/cppguide.html#Default_Arguments

Checks that constructors callable with a single argument and conversion operators are marked explicit to avoid the risk of unintentional implicit conversions.

Consider this example:

struct S {
  int x;
  operator bool() const { return true; }
};

bool f() {
  S a{1};
  S b{2};
  return a == b;
}

The function will return true, since the objects are implicitly converted to bool before comparison, which is unlikely to be the intent.

The check will suggest inserting explicit before the constructor or conversion operator declaration. However, copy and move constructors should not be explicit, as well as constructors taking a single initializer_list argument.

This code:

struct S {
  S(int a);
  explicit S(const S&);
  operator bool() const;
  ...

will become

struct S {
  explicit S(int a);
  S(const S&);
  explicit operator bool() const;
  ...

See https://google.github.io/styleguide/cppguide.html#Explicit_Constructors

Flag global namespace pollution in header files. Right now it only triggers on using declarations and directives.

The relevant style guide section is https://google.github.io/styleguide/cppguide.html#Namespaces.

Finds calls to +new or overrides of it, which are prohibited by the Google Objective-C style guide.

The Google Objective-C style guide forbids calling +new or overriding it in class implementations, preferring +alloc and -init methods to instantiate objects.

An example:

NSDate *now = [NSDate new];
Foo *bar = [Foo new];

Instead, code should use +alloc/-init or class factory methods.

NSDate *now = [NSDate date];
Foo *bar = [[Foo alloc] init];

This check corresponds to the Google Objective-C Style Guide rule Do Not Use +new.

Finds uses of throwing exceptions usages in Objective-C files.

For the same reason as the Google C++ style guide, we prefer not throwing exceptions from Objective-C code.

The corresponding C++ style guide rule: https://google.github.io/styleguide/cppguide.html#Exceptions

Instead, prefer passing in NSError ** and return BOOL to indicate success or failure.

A counterexample:

- (void)readFile {
  if ([self isError]) {
    @throw [NSException exceptionWithName:...];
  }
}

Instead, returning an error via NSError ** is preferred:

- (BOOL)readFileWithError:(NSError **)error {
  if ([self isError]) {
    *error = [NSError errorWithDomain:...];
    return NO;
  }
  return YES;
}

The corresponding style guide rule: https://google.github.io/styleguide/objcguide.html#avoid-throwing-exceptions

Finds function declarations in Objective-C files that do not follow the pattern described in the Google Objective-C Style Guide.

The corresponding style guide rule can be found here: https://google.github.io/styleguide/objcguide.html#function-names

All function names should be in Pascal case. Functions whose storage class is not static should have an appropriate prefix.

The following code sample does not follow this pattern:

static bool is_positive(int i) { return i > 0; }
bool IsNegative(int i) { return i < 0; }

The sample above might be corrected to the following code:

static bool IsPositive(int i) { return i > 0; }
bool *ABCIsNegative(int i) { return i < 0; }

Finds global variable declarations in Objective-C files that do not follow the pattern of variable names in Google's Objective-C Style Guide.

The corresponding style guide rule: https://google.github.io/styleguide/objcguide.html#variable-names

All the global variables should follow the pattern of g[A-Z].* (variables) or k[A-Z].* (constants). The check will suggest a variable name that follows the pattern if it can be inferred from the original name.

For code:

static NSString* myString = @"hello";

The fix will be:

static NSString* gMyString = @"hello";

Another example of constant:

static NSString* const myConstString = @"hello";

The fix will be:

static NSString* const kMyConstString = @"hello";

However for code that prefixed with non-alphabetical characters like:

static NSString* __anotherString = @"world";

The check will give a warning message but will not be able to suggest a fix. The user needs to fix it on their own.

Checks whether there are underscores in googletest test suite names and test names in test macros:

• TEST
• TEST_F
• TEST_P
• TYPED_TEST
• TYPED_TEST_P

The FRIEND_TEST macro is not included.

For example:

TEST(TestSuiteName, Illegal_TestName) {}
TEST(Illegal_TestSuiteName, TestName) {}

would trigger the check. Underscores are not allowed in test suite name nor test names.

The DISABLED_ prefix, which may be used to disable test suites and individual tests, is removed from the test suite name and test name before checking for underscores.

This check does not propose any fixes.

The google-readability-braces-around-statements check is an alias, please see readability-braces-around-statements for more information.

Finds usages of C-style casts.

https://google.github.io/styleguide/cppguide.html#Casting

Corresponding cpplint.py check name: readability/casting.

This check is similar to -Wold-style-cast, but it suggests automated fixes in some cases. The reported locations should not be different from the ones generated by -Wold-style-cast.

The google-readability-function-size check is an alias, please see readability-function-size for more information.

The google-readability-namespace-comments check is an alias, please see llvm-namespace-comment for more information.

Finds TODO comments without a username or bug number.

The relevant style guide section is https://google.github.io/styleguide/cppguide.html#TODO_Comments.

Corresponding cpplint.py check: readability/todo

Finds uses of short, long and long long and suggest replacing them with u?intXX(_t)?.

The corresponding style guide rule: https://google.github.io/styleguide/cppguide.html#Integer_Types.

Corresponding cpplint.py check: runtime/int.

UnsignedTypePrefix

A string specifying the unsigned type prefix. Default is uint.

SignedTypePrefix

A string specifying the signed type prefix. Default is int.

TypeSuffix

A string specifying the type suffix. Default is an empty string.

Finds overloads of unary operator &.

https://google.github.io/styleguide/cppguide.html#Operator_Overloading

Corresponding cpplint.py check name: runtime/operator.

Finds uses of deprecated Google Test version 1.9 APIs with names containing case and replaces them with equivalent APIs with suite.

All names containing case are being replaced to be consistent with the meanings of "test case" and "test suite" as used by the International Software Testing Qualifications Board and ISO 29119.

The new names are a part of Google Test version 1.9 (release pending). It is recommended that users update their dependency to version 1.9 and then use this check to remove deprecated names.

The affected APIs are:

• Member functions of testing::Test, testing::TestInfo, testing::TestEventListener, testing::UnitTest, and any type inheriting from these types
• The macros TYPED_TEST_CASE, TYPED_TEST_CASE_P, REGISTER_TYPED_TEST_CASE_P, and INSTANTIATE_TYPED_TEST_CASE_P
• The type alias testing::TestCase

Examples of fixes created by this check:

class FooTest : public testing::Test {
public:
  static void SetUpTestCase();
  static void TearDownTestCase();
};

TYPED_TEST_CASE(BarTest, BarTypes);

becomes

class FooTest : public testing::Test {
public:
  static void SetUpTestSuite();
  static void TearDownTestSuite();
};

TYPED_TEST_SUITE(BarTest, BarTypes);

For better consistency of user code, the check renames both virtual and non-virtual member functions with matching names in derived types. The check tries to provide only a warning when a fix cannot be made safely, as is the case with some template and macro uses.

The hicpp-avoid-c-arrays check is an alias, please see modernize-avoid-c-arrays for more information. It partly enforces the rule 4.1.1.

The hicpp-avoid-goto check is an alias, please see cppcoreguidelines-avoid-goto for more information. It enforces the rule 6.3.1.

The hicpp-braces-around-statements check is an alias, please see readability-braces-around-statements for more information. It enforces the rule 6.1.1.

The hicpp-deprecated-headers check is an alias, please see modernize-deprecated-headers for more information. It enforces the rule 1.3.3.

Ensure that every value that in a throw expression is an instance of std::exception.

This enforces rule 15.1 of the High Integrity C++ Coding Standard.

class custom_exception {};

void throwing() noexcept(false) {
  // Problematic throw expressions.
  throw int(42);
  throw custom_exception();
}

class mathematical_error : public std::exception {};

void throwing2() noexcept(false) {
  // These kind of throws are ok.
  throw mathematical_error();
  throw std::runtime_error();
  throw std::exception();
}

This check is an alias for google-explicit-constructor. Used to enforce parts of rule 5.4.1. This check will enforce that constructors and conversion operators are marked explicit. Other forms of casting checks are implemented in other places. The following checks can be used to check for more forms of casting:

• cppcoreguidelines-pro-type-static-cast-downcast
• cppcoreguidelines-pro-type-reinterpret-cast
• cppcoreguidelines-pro-type-const-cast
• cppcoreguidelines-pro-type-cstyle-cast

This check is an alias for readability-function-size. Useful to enforce multiple sections on function complexity.

• rule 8.2.2
• rule 8.3.1
• rule 8.3.2

Ensure that the result of std::remove, std::remove_if and std::unique are not ignored according to rule 17.5.1.

The mutating algorithms std::remove, std::remove_if and both overloads of std::unique operate by swapping or moving elements of the range they are operating over. On completion, they return an iterator to the last valid element. In the majority of cases the correct behavior is to use this result as the first operand in a call to std::erase.

This check is a subset of bugprone-unused-return-value and depending on used options it can be superfluous to enable both checks.

AllowCastToVoid

Controls whether casting return values to void is permitted. Default: true.

This check is an alias for bugprone-use-after-move.

Implements parts of the rule 8.4.1 to check if moved-from objects are accessed.

This check is an alias for cppcoreguidelines-pro-type-member-init. Implements the check for rule 12.4.2 to initialize class members in the right order.

The hicpp-move-const-arg check is an alias, please see performance-move-const-arg for more information. It enforces the rule 17.3.1.

This check discovers situations where code paths are not fully-covered. It furthermore suggests using if instead of switch if the code will be more clear. The rule 6.1.2 and rule 6.1.4 of the High Integrity C++ Coding Standard are enforced.

if-else if chains that miss a final else branch might lead to unexpected program execution and be the result of a logical error. If the missing else branch is intended you can leave it empty with a clarifying comment. This warning can be noisy on some code bases, so it is disabled by default.

void f1() {
  int i = determineTheNumber();

   if(i > 0) {
     // Some Calculation
   } else if (i < 0) {
     // Precondition violated or something else.
   }
   // ...
}

Similar arguments hold for switch statements which do not cover all possible code paths.

// The missing default branch might be a logical error. It can be kept empty
// if there is nothing to do, making it explicit.
void f2(int i) {
  switch (i) {
  case 0: // something
    break;
  case 1: // something else
    break;
  }
  // All other numbers?
}

// Violates this rule as well, but already emits a compiler warning (-Wswitch).
enum Color { Red, Green, Blue, Yellow };
void f3(enum Color c) {
  switch (c) {
  case Red: // We can't drive for now.
    break;
  case Green:  // We are allowed to drive.
    break;
  }
  // Other cases missing
}

The rule 6.1.4 requires every switch statement to have at least two case labels other than a default label. Otherwise, the switch could be better expressed with an if statement. Degenerated switch statements without any labels are caught as well.

// Degenerated switch that could be better written as `if`
int i = 42;
switch(i) {
  case 1: // do something here
  default: // do something else here
}

// Should rather be the following:
if (i == 1) {
  // do something here
}
else {
  // do something here
}

// A completely degenerated switch will be diagnosed.
int i = 42;
switch(i) {}

WarnOnMissingElse

Boolean flag that activates a warning for missing else branches. Default is false.

This check is an alias for readability-named-parameter.

Implements rule 8.2.1.

This check is an alias for misc-new-delete-overloads. Implements rule 12.3.1 to ensure the new and delete operators have the correct signature.

The hicpp-no-array-decay check is an alias, please see cppcoreguidelines-pro-bounds-array-to-pointer-decay for more information. It enforces the rule 4.1.1.

Checks for assembler statements. Use of inline assembly should be avoided since it restricts the portability of the code.

This enforces rule 7.5.1 of the High Integrity C++ Coding Standard.

The hicpp-no-malloc check is an alias, please see cppcoreguidelines-no-malloc for more information. It enforces the rule 5.3.2.

This check is an alias for performance-noexcept-move-constructor. Checks rule 12.5.4 to mark move assignment and move construction noexcept.

Finds uses of bitwise operations on signed integer types, which may lead to undefined or implementation defined behavior.

The according rule is defined in the High Integrity C++ Standard, Section 5.6.1.

IgnorePositiveIntegerLiterals

If this option is set to true, the check will not warn on bitwise operations with positive integer literals, e.g. ~0, 2 << 1, etc. Default value is false.

This check is an alias for cppcoreguidelines-special-member-functions. Checks that special member functions have the correct signature, according to rule 12.5.7.

The hicpp-static-assert check is an alias, please see misc-static-assert for more information. It enforces the rule 7.1.10.

This check is an alias for bugprone-undelegated-constructor. Partially implements rule 12.4.5 to find misplaced constructor calls inside a constructor.

struct Ctor {
  Ctor();
  Ctor(int);
  Ctor(int, int);
  Ctor(Ctor *i) {
    // All Ctor() calls result in a temporary object
    Ctor(); // did you intend to call a delegated constructor?
    Ctor(0); // did you intend to call a delegated constructor?
    Ctor(1, 2); // did you intend to call a delegated constructor?
    foo();
  }
};

The hicpp-uppercase-literal-suffix check is an alias, please see readability-uppercase-literal-suffix for more information.

Partially implements rule 4.2.1 to ensure that the U suffix is writeln properly.

The hicpp-use-auto check is an alias, please see modernize-use-auto for more information. It enforces the rule 7.1.8.

The hicpp-use-emplace check is an alias, please see modernize-use-emplace for more information. It enforces the rule 17.4.2.

This check is an alias for modernize-use-equals-default. Implements rule 12.5.1 to explicitly default special member functions.

This check is an alias for modernize-use-equals-delete. Implements rule 12.5.1 to explicitly default or delete special member functions.

The hicpp-use-noexcept check is an alias, please see modernize-use-noexcept for more information. It enforces the rule 1.3.5.

The hicpp-use-nullptr check is an alias, please see modernize-use-nullptr for more information. It enforces the rule 2.5.3.

This check is an alias for modernize-use-override. Implements rule 10.2.1 to declare a virtual function override when overriding.

The hicpp-vararg check is an alias, please see cppcoreguidelines-pro-type-vararg for more information. It enforces the rule 14.1.1.

Checks Linux kernel code to see if it uses the results from the functions in linux/err.h. Also checks to see if code uses the results from functions that directly return a value from one of these error functions.

This is important in the Linux kernel because ERR_PTR, PTR_ERR, IS_ERR, IS_ERR_OR_NULL, ERR_CAST, and PTR_ERR_OR_ZERO return values must be checked, since positive pointers and negative error codes are being used in the same context. These functions are marked with __attribute__((warn_unused_result)), but some kernel versions do not have this warning enabled for clang.

Examples:

/* Trivial unused call to an ERR function */
PTR_ERR_OR_ZERO(some_function_call());

/* A function that returns ERR_PTR. */
void *fn() { ERR_PTR(-EINVAL); }

/* An invalid use of fn. */
fn();

The llvm-else-after-return check is an alias, please see readability-else-after-return for more information.

Finds and fixes header guards that do not adhere to LLVM style.

Checks the correct order of #includes.

See https://llvm.org/docs/CodingStandards.html#include-style

google-readability-namespace-comments redirects here as an alias for this check.

Checks that long namespaces have a closing comment.

https://llvm.org/docs/CodingStandards.html#namespace-indentation

https://google.github.io/styleguide/cppguide.html#Namespaces

namespace n1 {
void f();
}

// becomes

namespace n1 {
void f();
}  // namespace n1

ShortNamespaceLines

Requires the closing brace of the namespace definition to be followed by a closing comment if the body of the namespace has more than ShortNamespaceLines lines of code. The value is an unsigned integer that defaults to 1U.

SpacesBeforeComments

An unsigned integer specifying the number of spaces before the comment closing a namespace definition. Default is 1U.

Looks at conditionals and finds and replaces cases of cast<>, which will assert rather than return a null pointer, and dyn_cast<> where the return value is not captured. Additionally, finds and replaces cases that match the pattern var && isa<X>(var), where var is evaluated twice.

// Finds these:
if (auto x = cast<X>(y)) {}
// is replaced by:
if (auto x = dyn_cast<X>(y)) {}

if (cast<X>(y)) {}
// is replaced by:
if (isa<X>(y)) {}

if (dyn_cast<X>(y)) {}
// is replaced by:
if (isa<X>(y)) {}

if (var && isa<T>(var)) {}
// is replaced by:
if (isa_and_nonnull<T>(var.foo())) {}

// Other cases are ignored, e.g.:
if (auto f = cast<Z>(y)->foo()) {}
if (cast<Z>(y)->foo()) {}
if (X.cast(y)) {}

Finds historical use of unsigned to hold vregs and physregs and rewrites them to use Register.

Currently this works by finding all variables of unsigned integer type whose initializer begins with an implicit cast from Register to unsigned.

void example(MachineOperand &MO) {
  unsigned Reg = MO.getReg();
  ...
}

becomes:

void example(MachineOperand &MO) {
  Register Reg = MO.getReg();
  ...
}

The llvm-qualified-auto check is an alias, please see readability-qualified-auto for more information.

Looks for local Twine variables which are prone to use after frees and should be generally avoided.

static Twine Moo = Twine("bark") + "bah";

// becomes

static std::string Moo = (Twine("bark") + "bah").str();

Checks all calls resolve to functions within correct namespace.

// Implementation inside the LIBC_NAMESPACE namespace.
// Correct if:
// - LIBC_NAMESPACE is a macro
// - LIBC_NAMESPACE expansion starts with `__llvm_libc`
namespace LIBC_NAMESPACE {

// Allow calls with the fully qualified name.
LIBC_NAMESPACE::strlen("hello");

// Allow calls to compiler provided functions.
(void)__builtin_abs(-1);

// Bare calls are allowed as long as they resolve to the correct namespace.
strlen("world");

// Disallow calling into functions in the global namespace.
::strlen("!");

} // namespace LIBC_NAMESPACE

Checks that all declarations in the llvm-libc implementation are within the correct namespace.

// Implementation inside the LIBC_NAMESPACE_DECL namespace.
// Correct if:
// - LIBC_NAMESPACE_DECL is a macro
// - LIBC_NAMESPACE_DECL expansion starts with `[[gnu::visibility("hidden")]] __llvm_libc`
namespace LIBC_NAMESPACE_DECL {
    void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
    // Namespaces within LIBC_NAMESPACE_DECL namespace are allowed.
    namespace inner {
        int localVar = 0;
    }
    // Functions with C linkage are allowed.
    extern "C" void str_fuzz() {}
}

// Incorrect: implementation not in the LIBC_NAMESPACE_DECL namespace.
void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}

// Incorrect: outer most namespace is not the LIBC_NAMESPACE_DECL macro.
namespace something_else {
    void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
}

// Incorrect: outer most namespace expansion does not start with `[[gnu::visibility("hidden")]] __llvm_libc`.
#define LIBC_NAMESPACE_DECL custom_namespace
namespace LIBC_NAMESPACE_DECL {
    void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
}

Checks that all implicitly and explicitly inline functions in header files are tagged with the LIBC_INLINE macro, except for functions implicit to classes or deleted functions. See the libc style guide for more information about this macro.

Finds includes of system libc headers not provided by the compiler within llvm-libc implementations.

#include <stdio.h>            // Not allowed because it is part of system libc.
#include <stddef.h>           // Allowed because it is provided by the compiler.
#include "internal/stdio.h"   // Allowed because it is NOT part of system libc.

This check is necessary because accidentally including system libc headers can lead to subtle and hard to detect bugs. For example consider a system libc whose dirent struct has slightly different field ordering than llvm-libc. While this will compile successfully, this can cause issues during runtime because they are ABI incompatible.

Includes

A string containing a comma separated glob list of allowed include filenames. Similar to the -checks glob list for running clang-tidy itself, the two wildcard characters are * and -, to include and exclude globs, respectively. The default is -*, which disallows all includes.

This can be used to allow known safe includes such as Linux development headers. See portability-restrict-system-includes for more details.

Warn about confusable identifiers, i.e. identifiers that are visually close to each other, but use different Unicode characters. This detects a potential attack described in CVE-2021-42574.

Example:

int fo; // Initial character is U+0066 (LATIN SMALL LETTER F).
int 𝐟o; // Initial character is U+1D41F (MATHEMATICAL BOLD SMALL F) not U+0066 (LATIN SMALL LETTER F).

This check implements detection of local variables which could be declared as const but are not. Declaring variables as const is required or recommended by many coding guidelines, such as: ES.25 from the C++ Core Guidelines and AUTOSAR C++14 Rule A7-1-1 (6.7.1 Specifiers).

Please note that this check's analysis is type-based only. Variables that are not modified but used to create a non-const handle that might escape the scope are not diagnosed as potential const.

// Declare a variable, which is not ``const`` ...
int i = 42;
// but use it as read-only. This means that `i` can be declared ``const``.
int result = i * i;       // Before transformation
int const result = i * i; // After transformation

The check can analyze values, pointers and references but not (yet) pointees:

// Normal values like built-ins or objects.
int potential_const_int = 42;       // Before transformation
int const potential_const_int = 42; // After transformation
int copy_of_value = potential_const_int;

MyClass could_be_const;       // Before transformation
MyClass const could_be_const; // After transformation
could_be_const.const_qualified_method();

// References can be declared const as well.
int &reference_value = potential_const_int;       // Before transformation
int const& reference_value = potential_const_int; // After transformation
int another_copy = reference_value;

// The similar semantics of pointers are not (yet) analyzed.
int *pointer_variable = &potential_const_int; // _NO_ 'const int *pointer_variable' suggestion.
int last_copy = *pointer_variable;

The automatic code transformation is only applied to variables that are declared in single declarations. You may want to prepare your code base with readability-isolate-declaration first.

Note that there is the check cppcoreguidelines-avoid-non-const-global-variables to enforce const correctness on all globals.

The check does not run on C code.

The check will not analyze templated variables or variables that are instantiation dependent. Different instantiations can result in different const correctness properties and in general it is not possible to find all instantiations of a template. The template might be used differently in an independent translation unit.

Pointees can not be analyzed for constness yet. The following code shows this limitation.

// Declare a variable that will not be modified.
int constant_value = 42;

// Declare a pointer to that variable, that does not modify either, but misses 'const'.
// Could be 'const int *pointer_to_constant = &constant_value;'
int *pointer_to_constant = &constant_value;

// Usage:
int result = 520 * 120 * (*pointer_to_constant);

This limitation affects the capability to add const to methods which is not possible, too.

AnalyzeValues (default = true)

Enable or disable the analysis of ordinary value variables, like int i = 42;

// Warning
int i = 42;
// No warning
int const i = 42;

// Warning
int a[] = {42, 42, 42};
// No warning
int const a[] = {42, 42, 42};

AnalyzeReferences (default = true)

Enable or disable the analysis of reference variables, like int &ref = i;

int i = 42;
// Warning
int& ref = i;
// No warning
int const& ref = i;

WarnPointersAsValues (default = false)

This option enables the suggestion for const of the pointer itself. Pointer values have two possibilities to be const, the pointer and the value pointing to.

int value = 42;

// Warning
const int * pointer_variable = &value;
// No warning
const int *const pointer_variable = &value;

TransformValues (default = true)

Provides fixit-hints for value types that automatically add const if its a single declaration.

// Before
int value = 42;
// After
int const value = 42;

// Before
int a[] = {42, 42, 42};
// After
int const a[] = {42, 42, 42};

// Result is modified later in its life-time. No diagnostic and fixit hint will be emitted.
int result = value * 3;
result -= 10;

TransformReferences (default = true)

Provides fixit-hints for reference types that automatically add const if its a single declaration.

// This variable could still be a constant. But because there is a non-const reference to
// it, it can not be transformed (yet).
int value = 42;
// The reference 'ref_value' is not modified and can be made 'const int &ref_value = value;'
// Before
int &ref_value = value;
// After
int const &ref_value = value;

// Result is modified later in its life-time. No diagnostic and fixit hint will be emitted.
int result = ref_value * 3;
result -= 10;

TransformPointersAsValues (default = false)

Provides fixit-hints for pointers if their pointee is not changed. This does not analyze if the value-pointed-to is unchanged!

Requires 'WarnPointersAsValues' to be 'true'.

int value = 42;

// Before
const int * pointer_variable = &value;
// After
const int *const pointer_variable = &value;

// Before
const int * a[] = {&value, &value};
// After
const int *const a[] = {&value, &value};

// Before
int *ptr_value = &value;
// After
int *const ptr_value = &value;

int result = 100 * (*ptr_value); // Does not modify the pointer itself.
// This modification of the pointee is still allowed and not diagnosed.
*ptr_value = 0;

// The following pointer may not become a 'int *const'.
int *changing_pointee = &value;
changing_pointee = &result;

Detects when objects of certain hostile RAII types persists across suspension points in a coroutine. Such hostile types include scoped-lockable types and types belonging to a configurable denylist.

Some objects require that they be destroyed on the same thread that created them. Traditionally this requirement was often phrased as "must be a local variable", under the assumption that local variables always work this way. However this is incorrect with C++20 coroutines, since an intervening co_await may cause the coroutine to suspend and later be resumed on another thread.

The lifetime of an object that requires being destroyed on the same thread must not encompass a co_await or co_yield point. If you create/destroy an object, you must do so without allowing the coroutine to suspend in the meantime.

Following types are considered as hostile:

• Scoped-lockable types: A scoped-lockable object persisting across a suspension point is problematic as the lock held by this object could be unlocked by a different thread. This would be undefined behaviour. This includes all types annotated with the scoped_lockable attribute.
• Types belonging to a configurable denylist.

// Call some async API while holding a lock.
task coro() {
  const std::lock_guard l(&mu_);

  // Oops! The async Bar function may finish on a different
  // thread from the one that created the lock_guard (and called
  // Mutex::Lock). After suspension, Mutex::Unlock will be called on the wrong thread.
  co_await Bar();
}

RAIITypesList

A semicolon-separated list of qualified types which should not be allowed to persist across suspension points. Eg: my::lockable; a::b;::my::other::lockable; The default value of this option is "std::lock_guard;std::scoped_lock".

AllowedAwaitablesList

A semicolon-separated list of qualified types of awaitables types which can be safely awaited while having hostile RAII objects in scope.

co_await-ing an expression of awaitable type is considered safe if the awaitable type is part of this list. RAII objects persisting across such a co_await expression are considered safe and hence are not flagged.

Example usage:

// Consider option AllowedAwaitablesList = "safe_awaitable"
struct safe_awaitable {
  bool await_ready() noexcept { return false; }
  void await_suspend(std::coroutine_handle<>) noexcept {}
  void await_resume() noexcept {}
};
auto wait() { return safe_awaitable{}; }

task coro() {
  // This persists across both the co_await's but is not flagged
  // because the awaitable is considered safe to await on.
  const std::lock_guard l(&mu_);
  co_await safe_awaitable{};
  co_await wait();
}

Eg: my::safe::awaitable;other::awaitable The default value of this option is empty string "".

Finds non-extern non-inline function and variable definitions in header files, which can lead to potential ODR violations in case these headers are included from multiple translation units.

// Foo.h
int a = 1; // Warning: variable definition.
extern int d; // OK: extern variable.

namespace N {
  int e = 2; // Warning: variable definition.
}

// Warning: variable definition.
const char* str = "foo";

// OK: internal linkage variable definitions are ignored for now.
// Although these might also cause ODR violations, we can be less certain and
// should try to keep the false-positive rate down.
static int b = 1;
const int c = 1;
const char* const str2 = "foo";
constexpr int k = 1;
namespace { int x = 1; }

// Warning: function definition.
int g() {
  return 1;
}

// OK: inline function definition is allowed to be defined multiple times.
inline int e() {
  return 1;
}

class A {
public:
  int f1() { return 1; } // OK: implicitly inline member function definition is allowed.
  int f2();

  static int d;
};

// Warning: not an inline member function definition.
int A::f2() { return 1; }

// OK: class static data member declaration is allowed.
int A::d = 1;

// OK: function template is allowed.
template<typename T>
T f3() {
  T a = 1;
  return a;
}

// Warning: full specialization of a function template is not allowed.
template <>
int f3() {
  int a = 1;
  return a;
}

template <typename T>
struct B {
  void f1();
};

// OK: member function definition of a class template is allowed.
template <typename T>
void B<T>::f1() {}

class CE {
  constexpr static int i = 5; // OK: inline variable definition.
};

inline int i = 5; // OK: inline variable definition.

constexpr int f10() { return 0; } // OK: constexpr function implies inline.

// OK: C++14 variable templates are inline.
template <class T>
constexpr T pi = T(3.1415926L);

When clang-tidy is invoked with the --fix-notes option, this check provides fixes that automatically add the inline keyword to discovered functions. Please note that the addition of the inline keyword to variables is not currently supported by this check.

Check detects cyclic #include dependencies between user-defined headers.

// Header A.hpp
#pragma once
#include "B.hpp"

// Header B.hpp
#pragma once
#include "C.hpp"

// Header C.hpp
#pragma once
#include "A.hpp"

// Include chain: A->B->C->A

Header files are a crucial part of many C++ programs as they provide a way to organize declarations and definitions shared across multiple source files. However, header files can also create problems when they become entangled in complex dependency cycles. Such cycles can cause issues with compilation times, unnecessary rebuilds, and make it harder to understand the overall structure of the code.

To address these issues, a check has been developed to detect cyclic dependencies between header files, also known as "include cycles". An include cycle occurs when a header file A includes header file B, and B (or any subsequent included header file) includes back header file A, resulting in a circular dependency cycle.

This check operates at the preprocessor level and specifically analyzes user-defined headers and their dependencies. It focuses solely on detecting include cycles while disregarding other types or function dependencies. This specialized analysis helps identify and prevent issues related to header file organization.

By detecting include cycles early in the development process, developers can identify and resolve these issues before they become more difficult and time-consuming to fix. This can lead to faster compile times, improved code quality, and a more maintainable codebase overall. Additionally, by ensuring that header files are organized in a way that avoids cyclic dependencies, developers can make their code easier to understand and modify over time.

It's worth noting that only user-defined headers their dependencies are analyzed, System includes such as standard library headers and third-party library headers are excluded. System includes are usually well-designed and free of include cycles, and ignoring them helps to focus on potential issues within the project's own codebase. This limitation doesn't diminish the ability to detect #include cycles within the analyzed code.

Developers should carefully review any warnings or feedback provided by this solution. While the analysis aims to identify and prevent include cycles, there may be situations where exceptions or modifications are necessary. It's important to exercise judgment and consider the specific context of the codebase when making adjustments.

IgnoredFilesList

Provides a way to exclude specific files/headers from the warnings raised by a check. This can be achieved by specifying a semicolon-separated list of regular expressions or filenames. This option can be used as an alternative to //NOLINT when using it is not possible. The default value of this option is an empty string, indicating that no files are ignored by default.

Checks for unused and missing includes. Generates findings only for the main file of a translation unit. Findings correspond to https://clangd.llvm.org/design/include-cleaner.

Example:

// foo.h
class Foo{};
// bar.h
#include "baz.h"
class Bar{};
// baz.h
class Baz{};
// main.cc
#include "bar.h" // OK: uses class Bar from bar.h
#include "foo.h" // warning: unused include "foo.h"
Bar bar;
Baz baz; // warning: missing include "baz.h"

IgnoreHeaders

A semicolon-separated list of regexes to disable insertion/removal of header files that match this regex as a suffix.  E.g., foo/.* disables insertion/removal for all headers under the directory foo. By default, no headers will be ignored.

DeduplicateFindings

A boolean that controls whether the check should deduplicate findings for the same symbol. Defaults to true.

Warn about unterminated bidirectional unicode sequence, detecting potential attack as described in the Trojan Source attack.

Example:

#include <iostream>

int main() {
    bool isAdmin = false;
    /*‮ } ⁦if (isAdmin)⁩ ⁦ begin admins only */
        std::cout << "You are an admin.\n";
    /* end admins only ‮ { ⁦*/
    return 0;
}

Finds identifiers that contain Unicode characters with right-to-left direction, which can be confusing as they may change the understanding of a whole statement line, as described in Trojan Source.

An example of such misleading code follows:

#include <stdio.h>

short int א = (short int)0;
short int ג = (short int)12345;

int main() {
  int א = ג; // a local variable, set to zero?
  printf("ג is %d\n", ג);
  printf("א is %d\n", א);
}

This check diagnoses when a const qualifier is applied to a typedef/ using to a pointer type rather than to the pointee, because such constructs are often misleading to developers because the const applies to the pointer rather than the pointee.

For instance, in the following code, the resulting type is int * const rather than const int *:

typedef int *int_ptr;
void f(const int_ptr ptr) {
  *ptr = 0; // potentially quite unexpectedly the int can be modified here
  ptr = 0; // does not compile
}

The check does not diagnose when the underlying typedef/using type is a pointer to a const type or a function pointer type. This is because the const qualifier is less likely to be mistaken because it would be redundant (or disallowed) on the underlying pointee type.

cert-dcl54-cpp redirects here as an alias for this check.

The check flags overloaded operator new() and operator delete() functions that do not have a corresponding free store function defined within the same scope. For instance, the check will flag a class implementation of a non-placement operator new() when the class does not also define a non-placement operator delete() function as well.

The check does not flag implicitly-defined operators, deleted or private operators, or placement operators.

This check corresponds to CERT C++ Coding Standard rule DCL54-CPP. Overload allocation and deallocation functions as a pair in the same scope.

Finds strongly connected functions (by analyzing the call graph for SCC's (Strongly Connected Components) that are loops), diagnoses each function in the cycle, and displays one example of a possible call graph loop (recursion).

References:

• CERT C++ Coding Standard rule DCL56-CPP. Avoid cycles during initialization of static objects.
• JPL Institutional Coding Standard for the C Programming Language (JPL DOCID D-60411) rule 2.4 Do not use direct or indirect recursion.
• OpenCL Specification, Version 1.2 rule 6.9 Restrictions: i. Recursion is not supported..

Limitations:

• The check does not handle calls done through function pointers
• The check does not handle C++ destructors

cert-fio38-c redirects here as an alias for this check.

The check flags dereferences and non-pointer declarations of objects that are not meant to be passed by value, such as C FILE objects or POSIX pthread_mutex_t objects.

This check corresponds to CERT C++ Coding Standard rule FIO38-C. Do not copy a FILE object.

cppcoreguidelines-non-private-member-variables-in-classes redirects here as an alias for this check.

Finds classes that contain non-static data members in addition to user-declared non-static member functions and diagnose all data members declared with a non-public access specifier. The data members should be declared as private and accessed through member functions instead of exposed to derived classes or class consumers.

IgnoreClassesWithAllMemberVariablesBeingPublic

Allows to completely ignore classes if all the member variables in that class a declared with a public access specifier.

IgnorePublicMemberVariables

Allows to ignore (not diagnose) all the member variables declared with a public access specifier.

Detect redundant expressions which are typically errors due to copy-paste.

Depending on the operator expressions may be

• redundant,
• always true,
• always false,
• always a constant (zero or one).

Examples:

((x+1) | (x+1))             // (x+1) is redundant
(p->x == p->x)              // always true
(p->x < p->x)               // always false
(speed - speed + 1 == 12)   // speed - speed is always zero

cert-dcl03-c redirects here as an alias for this check.

Replaces assert() with static_assert() if the condition is evaluable at compile time.

The condition of static_assert() is evaluated at compile time which is safer and more efficient.

cert-err09-cpp and cert-err61-cpp redirect here as aliases of this check.

Finds violations of the rule "Throw by value, catch by reference" presented for example in "C++ Coding Standards" by H. Sutter and A. Alexandrescu, as well as the CERT C++ Coding Standard rule ERR61-CPP. Catch exceptions by lvalue reference.

Exceptions:

• Throwing string literals will not be flagged despite being a pointer. They are not susceptible to slicing and the usage of string literals is idiomatic.
• Catching character pointers (char, wchar_t, unicode character types) will not be flagged to allow catching string literals.
• Moved named values will not be flagged as not throwing an anonymous temporary. In this case we can be sure that the user knows that the object can't be accessed outside catch blocks handling the error.
• Throwing function parameters will not be flagged as not throwing an anonymous temporary. This allows helper functions for throwing.
• Re-throwing caught exception variables will not be flagged as not throwing an anonymous temporary. Although this can usually be done by just writing throw; it happens often enough in real code.

CheckThrowTemporaries

Triggers detection of violations of the CERT recommendation ERR09-CPP. Throw anonymous temporaries. Default is true.

WarnOnLargeObject

Also warns for any large, trivial object caught by value. Catching a large object by value is not dangerous but affects the performance negatively. The maximum size of an object allowed to be caught without warning can be set using the MaxSize option. Default is false.

MaxSize

Determines the maximum size of an object allowed to be caught without warning. Only applicable if WarnOnLargeObject is set to true. If the option is set by the user to std::numeric_limits<uint64_t>::max() then it reverts to the default value. Default is the size of size_t.

Finds declarations of assign operators with the wrong return and/or argument types and definitions with good return type but wrong return statements.

• The return type must be Class&.
• The assignment may be from the class type by value, const lvalue reference, non-const rvalue reference, or from a completely different type (e.g. int).
• Private and deleted operators are ignored.
• The operator must always return *this.

This check implements AUTOSAR C++14 Rule A13-2-1.

Find and replace unique_ptr::reset(release()) with std::move().

Example:

std::unique_ptr<Foo> x, y;
x.reset(y.release()); -> x = std::move(y);

If y is already rvalue, std::move() is not added. x and y can also be std::unique_ptr<Foo>*.

IncludeStyle

A string specifying which include-style is used, llvm or google. Default is llvm.

Finds unused namespace alias declarations.

namespace my_namespace {
class C {};
}
namespace unused_alias = ::my_namespace;

Finds unused function parameters. Unused parameters may signify a bug in the code (e.g. when a different parameter is used instead). The suggested fixes either comment parameter name out or remove the parameter completely, if all callers of the function are in the same translation unit and can be updated.

The check is similar to the -Wunused-parameter compiler diagnostic and can be used to prepare a codebase to enabling of that diagnostic. By default the check is more permissive (see StrictMode).

void a(int i) { /*some code that doesn't use `i`*/ }

// becomes

void a(int  /*i*/) { /*some code that doesn't use `i`*/ }

static void staticFunctionA(int i);
static void staticFunctionA(int i) { /*some code that doesn't use `i`*/ }

// becomes

static void staticFunctionA()
static void staticFunctionA() { /*some code that doesn't use `i`*/ }

StrictMode

When false (default value), the check will ignore trivially unused parameters, i.e. when the corresponding function has an empty body (and in case of constructors - no constructor initializers). When the function body is empty, an unused parameter is unlikely to be unnoticed by a human reader, and there's basically no place for a bug to hide.

IgnoreVirtual

Determines whether virtual method parameters should be inspected. Set to true to ignore them. Default is false.

Finds unused using declarations.

Unused using` declarations in header files will not be diagnosed since these using declarations are part of the header's public API. Allowed header file extensions can be configured via the global option HeaderFileExtensions.

Example:

// main.cpp
namespace n { class C; }
using n::C;  // Never actually used.

Finds instances of static functions or variables declared at global scope that could instead be moved into an anonymous namespace.

Anonymous namespaces are the "superior alternative" according to the C++ Standard. static was proposed for deprecation, but later un-deprecated to keep C compatibility [1]. static is an overloaded term with different meanings in different contexts, so it can create confusion.

The following uses of static will not be diagnosed:

• Functions or variables in header files, since anonymous namespaces in headers is considered an antipattern. Allowed header file extensions can be configured via the global option HeaderFileExtensions.
• const or constexpr variables, since they already have implicit internal linkage in C++.

Examples:

// Bad
static void foo();
static int x;

// Good
namespace {
  void foo();
  int x;
} // namespace

[1] Undeprecating static

Detects variables and functions that can be marked as static or moved into an anonymous namespace to enforce internal linkage.

Static functions and variables are scoped to a single file. Marking functions and variables as static helps to better remove dead code. In addition, it gives the compiler more information and allows for more aggressive optimizations.

Example:

int v1; // can be marked as static

void fn1(); // can be marked as static

namespace {
  // already in anonymous namespace
  int v2;
  void fn2();
}
// already declared as extern
extern int v2;

FixMode

Selects what kind of a fix the check should provide. The default is UseStatic.

None

Don't fix automatically.

UseStatic

Add static for internal linkage variable and function.

The check finds uses of std::bind and boost::bind and replaces them with lambdas. Lambdas will use value-capture unless reference capture is explicitly requested with std::ref or boost::ref.

It supports arbitrary callables including member functions, function objects, and free functions, and all variations thereof. Anything that you can pass to the first argument of bind should be diagnosable. Currently, the only known case where a fix-it is unsupported is when the same placeholder is specified multiple times in the parameter list.

Given:

int add(int x, int y) { return x + y; }

Then:

void f() {
  int x = 2;
  auto clj = std::bind(add, x, _1);
}

is replaced by:

void f() {
  int x = 2;
  auto clj = [=](auto && arg1) { return add(x, arg1); };
}

std::bind can be hard to read and can result in larger object files and binaries due to type information that will not be produced by equivalent lambdas.

PermissiveParameterList

If the option is set to true, the check will append auto&&... to the end of every placeholder parameter list. Without this, it is possible for a fix-it to perform an incorrect transformation in the case where the result of the bind is used in the context of a type erased functor such as std::function which allows mismatched arguments. For example:

int add(int x, int y) { return x + y; }
int foo() {
  std::function<int(int,int)> ignore_args = std::bind(add, 2, 2);
  return ignore_args(3, 3);
}

is valid code, and returns 4. The actual values passed to ignore_args are simply ignored. Without PermissiveParameterList, this would be transformed into

int add(int x, int y) { return x + y; }
int foo() {
  std::function<int(int,int)> ignore_args = [] { return add(2, 2); }
  return ignore_args(3, 3);
}

which will not compile, since the lambda does not contain an operator() that accepts 2 arguments. With permissive parameter list, it instead generates

int add(int x, int y) { return x + y; }
int foo() {
  std::function<int(int,int)> ignore_args = [](auto&&...) { return add(2, 2); }
  return ignore_args(3, 3);
}

which is correct.

This check requires using C++14 or higher to run.

cppcoreguidelines-avoid-c-arrays redirects here as an alias for this check.

hicpp-avoid-c-arrays redirects here as an alias for this check.

Finds C-style array types and recommend to use std::array<> / std::vector<>. All types of C arrays are diagnosed.

However, fix-it are potentially dangerous in header files and are therefore not emitted right now.

int a[] = {1, 2}; // warning: do not declare C-style arrays, use std::array<> instead

int b[1]; // warning: do not declare C-style arrays, use std::array<> instead

void foo() {
  int c[b[0]]; // warning: do not declare C VLA arrays, use std::vector<> instead
}

template <typename T, int Size>
class array {
  T d[Size]; // warning: do not declare C-style arrays, use std::array<> instead

  int e[1]; // warning: do not declare C-style arrays, use std::array<> instead
};

array<int[4], 2> d; // warning: do not declare C-style arrays, use std::array<> instead

using k = int[4]; // warning: do not declare C-style arrays, use std::array<> instead

However, the extern "C" code is ignored, since it is common to share such headers between C code, and C++ code.

// Some header
extern "C" {

int f[] = {1, 2}; // not diagnosed

int j[1]; // not diagnosed

inline void bar() {
  {
    int j[j[0]]; // not diagnosed
  }
}

}

Similarly, the main() function is ignored. Its second and third parameters can be either char* argv[] or char** argv, but cannot be std::array<>.

AllowStringArrays

When set to true (default is false), variables of character array type with deduced length, initialized directly from string literals, will be ignored. This option doesn't affect cases where length can't be deduced, resembling pointers, as seen in class members and parameters. Example:

const char name[] = "Some name";

Checks for use of nested namespaces such as namespace a { namespace b { ... } } and suggests changing to the more concise syntax introduced in C++17: namespace a::b { ... }. Inline namespaces are not modified.

For example:

namespace n1 {
namespace n2 {
void t();
}
}

namespace n3 {
namespace n4 {
namespace n5 {
void t();
}
}
namespace n6 {
namespace n7 {
void t();
}
}
}

// in c++20
namespace n8 {
inline namespace n9 {
void t();
}
}

Will be modified to:

namespace n1::n2 {
void t();
}

namespace n3 {
namespace n4::n5 {
void t();
}
namespace n6::n7 {
void t();
}
}

// in c++20
namespace n8::inline n9 {
void t();
}

Some headers from C library were deprecated in C++ and are no longer welcome in C++ codebases. Some have no effect in C++. For more details refer to the C++14 Standard [depr.c.headers] section.

This check replaces C standard library headers with their C++ alternatives and removes redundant ones.

// C++ source file...
#include <assert.h>
#include <stdbool.h>

// becomes

#include <cassert>
// No 'stdbool.h' here.

Important note: the Standard doesn't guarantee that the C++ headers declare all the same functions in the global namespace. The check in its current form can break the code that uses library symbols from the global namespace.

• <assert.h>
• <complex.h>
• <ctype.h>
• <errno.h>
• <fenv.h>     // deprecated since C++11
• <float.h>
• <inttypes.h>
• <limits.h>
• <locale.h>
• <math.h>
• <setjmp.h>
• <signal.h>
• <stdarg.h>
• <stddef.h>
• <stdint.h>
• <stdio.h>
• <stdlib.h>
• <string.h>
• <tgmath.h>   // deprecated since C++11
• <time.h>
• <uchar.h>    // deprecated since C++11
• <wchar.h>
• <wctype.h>

If the specified standard is older than C++11 the check will only replace headers deprecated before C++11, otherwise -- every header that appeared in the previous list.

These headers don't have effect in C++:

• <iso646.h>
• <stdalign.h>
• <stdbool.h>

The checker ignores include directives within extern "C" { ... } blocks, since a library might want to expose some API for C and C++ libraries.

// C++ source file...
extern "C" {
#include <assert.h>  // Left intact.
#include <stdbool.h> // Left intact.
}

CheckHeaderFile

clang-tidy cannot know if the header file included by the currently analyzed C++ source file is not included by any other C source files. Hence, to omit false-positives and wrong fixit-hints, we ignore emitting reports into header files. One can set this option to true if they know that the header files in the project are only used by C++ source file. Default is false.

Detects usage of the deprecated member types of std::ios_base and replaces those that have a non-deprecated equivalent.

This check converts for(...; ...; ...) loops to use the new range-based loops in C++11.

Three kinds of loops can be converted:

• Loops over statically allocated arrays.
• Loops over containers, using iterators.
• Loops over array-like containers, using operator[] and at().

In loops where the container expression is more complex than just a reference to a declared expression (a variable, function, enum, etc.), and some part of it appears elsewhere in the loop, we lower our confidence in the transformation due to the increased risk of changing semantics. Transformations for these loops are marked as risky, and thus will only be converted if the minimum required confidence level is set to risky.

int arr[10][20];
int l = 5;

for (int j = 0; j < 20; ++j)
  int k = arr[l][j] + l; // using l outside arr[l] is considered risky

for (int i = 0; i < obj.getVector().size(); ++i)
  obj.foo(10); // using 'obj' is considered risky

See Range-based loops evaluate end() only once for an example of an incorrect transformation when the minimum required confidence level is set to risky.

If a loop calls .end() or .size() after each iteration, the transformation for that loop is marked as reasonable, and thus will be converted if the required confidence level is set to reasonable (default) or lower.

// using size() is considered reasonable
for (int i = 0; i < container.size(); ++i)
  cout << container[i];

Any other loops that do not match the above criteria to be marked as risky or reasonable are marked safe, and thus will be converted if the required confidence level is set to safe or lower.

int arr[] = {1,2,3};

for (int i = 0; i < 3; ++i)
  cout << arr[i];

Original:

const int N = 5;
int arr[] = {1,2,3,4,5};
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);

// safe conversion
for (int i = 0; i < N; ++i)
  cout << arr[i];

// reasonable conversion
for (vector<int>::iterator it = v.begin(); it != v.end(); ++it)
  cout << *it;

// reasonable conversion
for (vector<int>::iterator it = begin(v); it != end(v); ++it)
  cout << *it;

// reasonable conversion
for (vector<int>::iterator it = std::begin(v); it != std::end(v); ++it)
  cout << *it;

// reasonable conversion
for (int i = 0; i < v.size(); ++i)
  cout << v[i];

// reasonable conversion
for (int i = 0; i < size(v); ++i)
  cout << v[i];

After applying the check with minimum confidence level set to reasonable (default):

const int N = 5;
int arr[] = {1,2,3,4,5};
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);

// safe conversion
for (auto & elem : arr)
  cout << elem;

// reasonable conversion
for (auto & elem : v)
  cout << elem;

// reasonable conversion
for (auto & elem : v)
  cout << elem;

The converter is also capable of transforming iterator loops which use rbegin and rend for looping backwards over a container. Out of the box this will automatically happen in C++20 mode using the ranges library, however the check can be configured to work without C++20 by specifying a function to reverse a range and optionally the header file where that function lives.

UseCxx20ReverseRanges

When set to true convert loops when in C++20 or later mode using std::ranges::reverse_view. Default value is true.

MakeReverseRangeFunction

Specify the function used to reverse an iterator pair, the function should accept a class with rbegin and rend methods and return a class with begin and end methods that call the rbegin and rend methods respectively. Common examples are ranges::reverse_view and llvm::reverse. Default value is an empty string.

MakeReverseRangeHeader

Specifies the header file where MakeReverseRangeFunction is declared. For the previous examples this option would be set to range/v3/view/reverse.hpp and llvm/ADT/STLExtras.h respectively. If this is an empty string and MakeReverseRangeFunction is set, the check will proceed on the assumption that the function is already available in the translation unit. This can be wrapped in angle brackets to signify to add the include as a system include. Default value is an empty string.

IncludeStyle

A string specifying which include-style is used, llvm or google. Default is llvm.

There are certain situations where the tool may erroneously perform transformations that remove information and change semantics. Users of the tool should be aware of the behavior and limitations of the check outlined by the cases below.

Comments inside the original loop header are ignored and deleted when transformed.

for (int i = 0; i < N; /* This will be deleted */ ++i) { }

The C++11 range-based for loop calls .end() only once during the initialization of the loop. If in the original loop .end() is called after each iteration the semantics of the transformed loop may differ.

// The following is semantically equivalent to the C++11 range-based for loop,
// therefore the semantics of the header will not change.
for (iterator it = container.begin(), e = container.end(); it != e; ++it) { }

// Instead of calling .end() after each iteration, this loop will be
// transformed to call .end() only once during the initialization of the loop,
// which may affect semantics.
for (iterator it = container.begin(); it != container.end(); ++it) { }

As explained above, calling member functions of the container in the body of the loop is considered risky. If the called member function modifies the container the semantics of the converted loop will differ due to .end() being called only once.

bool flag = false;
for (vector<T>::iterator it = vec.begin(); it != vec.end(); ++it) {
  // Add a copy of the first element to the end of the vector.
  if (!flag) {
    // This line makes this transformation 'risky'.
    vec.push_back(*it);
    flag = true;
  }
  cout << *it;
}

The original code above prints out the contents of the container including the newly added element while the converted loop, shown below, will only print the original contents and not the newly added element.

bool flag = false;
for (auto & elem : vec) {
  // Add a copy of the first element to the end of the vector.
  if (!flag) {
    // This line makes this transformation 'risky'
    vec.push_back(elem);
    flag = true;
  }
  cout << elem;
}

Semantics will also be affected if .end() has side effects. For example, in the case where calls to .end() are logged the semantics will change in the transformed loop if .end() was originally called after each iteration.

iterator end() {
  num_of_end_calls++;
  return container.end();
}

Similarly, if operator->() was overloaded to have side effects, such as logging, the semantics will change. If the iterator's operator->() was used in the original loop it will be replaced with <container element>.<member> instead due to the implicit dereference as part of the range-based for loop. Therefore any side effect of the overloaded operator->() will no longer be performed.

for (iterator it = c.begin(); it != c.end(); ++it) {
  it->func(); // Using operator->()
}
// Will be transformed to:
for (auto & elem : c) {
  elem.func(); // No longer using operator->()
}

While most of the check's risk analysis is dedicated to determining whether the iterator or container was modified within the loop, it is possible to circumvent the analysis by accessing and modifying the container through a pointer or reference.

If the container were directly used instead of using the pointer or reference the following transformation would have only been applied at the risky level since calling a member function of the container is considered risky. The check cannot identify expressions associated with the container that are different than the one used in the loop header, therefore the transformation below ends up being performed at the safe level.

vector<int> vec;

vector<int> *ptr = &vec;
vector<int> &ref = vec;

for (vector<int>::iterator it = vec.begin(), e = vec.end(); it != e; ++it) {
  if (!flag) {
    // Accessing and modifying the container is considered risky, but the risk
    // level is not raised here.
    ptr->push_back(*it);
    ref.push_back(*it);
    flag = true;
  }
}

As range-based for loops are only available since OpenMP 5, this check should not be used on code with a compatibility requirement of OpenMP prior to version 5. It is intentional that this check does not make any attempts to exclude incorrect diagnostics on OpenMP for loops prior to OpenMP 5.

To prevent this check to be applied (and to break) OpenMP for loops but still be applied to non-OpenMP for loops the usage of NOLINT (see Suppressing Undesired Diagnostics) on the specific for loops is recommended.

Replaces groups of adjacent macros with an unscoped anonymous enum. Using an unscoped anonymous enum ensures that everywhere the macro token was used previously, the enumerator name may be safely used.

This check can be used to enforce the C++ core guideline Enum.1: Prefer enumerations over macros, within the constraints outlined below.

Potential macros for replacement must meet the following constraints:

• Macros must expand only to integral literal tokens or expressions of literal tokens.  The expression may contain any of the unary operators -, +, ~ or !, any of the binary operators ,, -, +, *, /, %, &, |, ^, <, >, <=, >=, ==, !=, ||, &&, <<, >> or <=>, the ternary operator ?: and its GNU extension. Parenthesized expressions are also recognized.  This recognizes most valid expressions.  In particular, expressions with the sizeof operator are not recognized.
• Macros must be defined on sequential source file lines, or with only comment lines in between macro definitions.
• Macros must all be defined in the same source file.
• Macros must not be defined within a conditional compilation block. (Conditional include guards are exempt from this constraint.)
• Macros must not be defined adjacent to other preprocessor directives.
• Macros must not be used in any conditional preprocessing directive.
• Macros must not be used as arguments to other macros.
• Macros must not be undefined.
• Macros must be defined at the top-level, not inside any declaration or definition.