EXTRACLANGTOOLS(1)

NAME
extraclangtools - Extra Clang Tools Documentation

Welcome to the clang-tools-extra project which contains extra tools built using Clang’s tooling API’s.

EXTRA CLANG TOOLS 4.0.0 RELEASE NOTES

•   Introduction

•   What’s New in Extra Clang Tools 4.0.0?

•   Improvements to clang-tidy

•   Improvements to include-fixer

    Written by the LLVM Team

  Introduction

This document contains the release notes for the Extra Clang Tools, part of the Clang release 4.0.0. 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.

  What’s New in Extra Clang Tools 4.0.0?

Some of the major new features and improvements to Extra Clang Tools are listed here.

  Improvements to clang-tidy

•   New cppcoreguidelines-slicing check

    Flags slicing of member variables or vtable.

•   New cppcoreguidelines-special-member-functions check

    Flags classes where some, but not all, special member functions are user-defined.

•   The UseCERTSemantics option for the misc-move-constructor-init check has been removed as it duplicated the modernize-pass-by-value check.

•   New misc-move-forwarding-reference check

    Warns when std::move is applied to a forwarding reference instead of std::forward.

•   misc-pointer-and-integral-operation check was removed.

•   New misc-string-compare check

    Warns about using compare to test for string equality or inequality.

•   New misc-use-after-move check

    Warns if an object is used after it has been moved, without an intervening reinitialization.

•   New cppcoreguidelines-no-malloc check warns if C-style memory management is used and suggests the use of RAII.

•   modernize-make-unique and modernize-make-shared now handle calls to the smart pointer’s reset() method.

•   The modernize-pass-by-value check now has a ValuesOnly option to only warn about parameters that are passed by value but not moved.

•   The modernize-use-auto check now warns about variable declarations that are initialized with a cast, or by calling a templated function that behaves as a cast.

•   The modernize-use-default check has been renamed to modernize-use-equals-default.

•   New modernize-use-default-member-init check

    Converts a default constructor’s member initializers into default member initializers. Removes member initializers that are the same as a default member initializer.

•   New modernize-use-equals-delete check

    Adds = delete to unimplemented private special member functions.

•   New modernize-use-transparent-functors check

    Replaces uses of non-transparent functors with transparent ones where applicable.

•   New mpi-buffer-deref check

    Flags buffers which are insufficiently dereferenced when passed to an MPI function call.

•   New mpi-type-mismatch check

    Flags MPI function calls with a buffer type and MPI data type mismatch.

•   New performance-inefficient-string-concatenation check

    Warns about the performance overhead arising from concatenating strings using the operator+, instead of operator+=.

•   New performance-type-promotion-in-math-fn check

    Replaces uses of C-style standard math functions with double parameters and float arguments with an equivalent function that takes a float parameter.

•   readability-container-size-empty check supports arbitrary containers with with suitable empty() and size() methods.

•   New readability-misplaced-array-index check

    Warns when there is array index before the [] instead of inside it.

•   New readability-non-const-parameter check

    Flags function parameters of a pointer type that could be changed to point to a constant type instead.

•   New readability-redundant-declaration check

    Finds redundant variable and function declarations.

•   New readability-redundant-function-ptr-dereference check

    Finds redundant function pointer dereferences.

•   New readability-redundant-member-init check

    Flags member initializations that are unnecessary because the same default constructor would be called if they were not present.

•   The readability-redundant-string-cstr check now warns about redundant calls to data() too.

•   The google-explicit-constructor check now warns about conversion operators not marked explicit.

    Fixed bugs:

•   modernize-make-unique and modernize-make-shared Calling make_{unique|shared} from within a member function of a type with a private or protected constructor would be ill-formed.

  Improvements to include-fixer

•   Emacs integration was added.

CLANG-TIDY

  Contents

•   Clang-Tidy

•   Using clang-tidy

•   Getting Involved

•   Choosing the Right Place for your Check

•   Preparing your Workspace

•   The Directory Structure

•   Writing a clang-tidy Check

•   Registering your Check

•   Configuring Checks

•   Testing Checks

•   Running clang-tidy on LLVM

    See also:

  Clang-Tidy Checks

  boost-use-to-string

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 behaviour.

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);

  cert-dcl03-c

The cert-dcl03-c check is an alias, please see misc-static-assert for more information.

  cert-dcl50-cpp

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.

  cert-dcl54-cpp

The cert-dcl54-cpp check is an alias, please see misc-new-delete-overloads for more information.

  cert-dcl59-cpp

The cert-dcl59-cpp check is an alias, please see google-build-namespaces for more information.

  cert-env33-c

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().

  cert-err09-cpp

The cert-err09-cpp check is an alias, please see misc-throw-by-value-catch-by-reference for more information.

  cert-err34-c

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.

  cert-err52-cpp

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().

  cert-err58-cpp

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.

  cert-err60-cpp

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.

  cert-err61-cpp

The cert-err61-cpp check is an alias, please see misc-throw-by-value-catch-by-reference for more information.

  cert-fio38-c

The cert-fio38-c check is an alias, please see misc-non-copyable-objects for more information.

  cert-flp30-c

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.

  cert-msc30-c

The cert-msc30-c check is an alias, please see cert-msc50-cpp for more information.

  cert-msc50-cpp

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().

  cert-oop11-cpp

The cert-oop11-cpp check is an alias, please see misc-move-constructor-init for more information.

  cppcoreguidelines-interfaces-global-init

This check flags initializers of globals that access extern objects, and therefore can lead to order-of-initialization problems.

This rule is part of the “Interfaces” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Ri-global-init

Note that currently this does not flag calls to non-constexpr functions, and therefore globals could still be accessed from functions themselves.

  cppcoreguidelines-no-malloc

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. See C++ Core Guidelines <https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Rr-mallocfree>.

There is no attempt made to provide fixit 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));

  cppcoreguidelines-pro-bounds-array-to-pointer-decay

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” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-bounds-decay.

  cppcoreguidelines-pro-bounds-constant-array-index

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” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-bounds-arrayindex.

  Options

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.

  cppcoreguidelines-pro-bounds-pointer-arithmetic

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” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-bounds-arithmetic.

  cppcoreguidelines-pro-type-const-cast

This check flags all uses of const_cast in C++ code.

Modifying a variable that was declared const is undefined behavior, even with const_cast.

This rule is part of the “Type safety” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-type-constcast.

  cppcoreguidelines-pro-type-cstyle-cast

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” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-type-cstylecast.

  cppcoreguidelines-pro-type-member-init

The check flags user-defined 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.

  Options

IgnoreArrays
    If set to non-zero, 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 0.

    This rule is part of the “Type safety” profile of the C++ Core Guidelines, corresponding to rule Type.6. See https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-type-memberinit.

  cppcoreguidelines-pro-type-reinterpret-cast

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” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-type-reinterpretcast.

  cppcoreguidelines-pro-type-static-cast-downcast

This check flags all usages of static_cast, where a base class is casted to a derived class. In those cases, a fixit 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” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-type-downcast.

  cppcoreguidelines-pro-type-union-access

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” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-type-unions.

  cppcoreguidelines-pro-type-vararg

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.

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” profile of the C++ Core Guidelines, see https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Pro-type-varargs.

  cppcoreguidelines-slicing

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.

See the relevant C++ Core Guidelines sections for details: https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es63-dont-slice https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c145-access-polymorphic-objects-through-pointers-and-references

  cppcoreguidelines-special-member-functions

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 rule is part of the “Constructors, assignments, and destructors” profile of the C++ Core Guidelines, corresponding to rule C.21. See

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c21-if-you-define-or-delete-any-default-operation-define-or-delete-them-all.

  google-build-explicit-make-pair

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.

  google-build-namespaces

cert-dcl59-cpp 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.

  Options

HeaderFileExtensions
    A comma-separated list of filename extensions of header files (the filename extensions should not include “.” prefix). Default is “h,hh,hpp,hxx”. For header files without an extension, use an empty string (if there are no other desired extensions) or leave an empty element in the list. e.g., “h,hh,hpp,hxx,” (note the trailing comma).

  google-build-using-namespace

Finds using namespace directives.

The check implements the following rule of the Google C++ Style Guide: You may not use a using-directive to make all names from a namespace available.

// Forbidden -- This pollutes the namespace.
using namespace foo;

Corresponding cpplint.py check name: build/namespaces.

  google-default-arguments

Checks that default arguments are not given for virtual methods.

See https://google.github.io/styleguide/cppguide.html#Default_Arguments

  google-explicit-constructor

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

  google-global-names-in-headers

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.

  Options

HeaderFileExtensions
    A comma-separated list of filename extensions of header files (the filename extensions should not contain “.” prefix). Default is “h”. For header files without an extension, use an empty string (if there are no other desired extensions) or leave an empty element in the list. e.g., “h,hh,hpp,hxx,” (note the trailing comma).

  google-readability-braces-around-statements

The google-readability-braces-around-statements check is an alias, please see readability-braces-around-statements for more information.

  google-readability-casting

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.

  google-readability-function-size

The google-readability-function-size check is an alias, please see readability-function-size for more information.

  google-readability-namespace-comments

The google-readability-namespace-comments check is an alias, please see llvm-namespace-comment for more information.

  google-readability-redundant-smartptr-get

The google-readability-redundant-smartptr-get check is an alias, please see readability-redundant-smartptr-get for more information.

  google-readability-todo

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

  google-runtime-int

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.

Correspondig cpplint.py check: runtime/int.

  Options

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.

  google-runtime-member-string-references

Finds members of type const string&.

const string reference members are generally considered unsafe as they can be created from a temporary quite easily.

struct S {
  S(const string &Str) : Str(Str) {}
  const string &Str;
};
S instance("string");

In the constructor call a string temporary is created from const char * and destroyed immediately after the call. This leaves around a dangling reference.

This check emit warnings for both std::string and ::string const reference members.

Corresponding cpplint.py check name: runtime/member_string_reference.

  google-runtime-memset

Finds calls to memset with a literal zero in the length argument.

This is most likely unintended and the length and value arguments are swapped.

Corresponding cpplint.py check name: runtime/memset.

  google-runtime-operator

Finds overloads of unary operator &.

https://google.github.io/styleguide/cppguide.html#Operator_Overloading

Corresponding cpplint.py check name: runtime/operator.

  google-runtime-references

Checks the usage of non-constant references in function parameters.

The corresponding style guide rule: https://google.github.io/styleguide/cppguide.html#Reference_Arguments

  Options

WhiteListTypes
    A semicolon-separated list of names of whitelist types. Default is empty.

  llvm-header-guard

Finds and fixes header guards that do not adhere to LLVM style.

  Options

HeaderFileExtensions
    A comma-separated list of filename extensions of header files (the filename extensions should not include “.” prefix). Default is “h,hh,hpp,hxx”. For header files without an extension, use an empty string (if there are no other desired extensions) or leave an empty element in the list. e.g., “h,hh,hpp,hxx,” (note the trailing comma).

  llvm-include-order

Checks the correct order of #includes.

See http://llvm.org/docs/CodingStandards.html#include-style

  llvm-namespace-comment

google-readability-namespace-comments redirects here as an alias for this check.

Checks that long namespaces have a closing comment.

http://llvm.org/docs/CodingStandards.html#namespace-indentation

https://google.github.io/styleguide/cppguide.html#Namespaces

  Options

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.

  llvm-twine-local

Looks for local Twine variables which are prone to use after frees and should be generally avoided.

  misc-argument-comment

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.

  Options

StrictMode
    When non-zero, the check will ignore leading and trailing underscores and case when comparing parameter names.

  misc-assert-side-effect

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.

  Options

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.

  misc-bool-pointer-implicit-conversion

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.
}

  misc-dangling-handle

Detect dangling references in value handles like std::experimental::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;
}

  Options

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

  misc-definitions-in-headers

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";
// 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() {}

  Options

HeaderFileExtensions
    A comma-separated list of filename extensions of header files (the filename extensions should not include “.” prefix). Default is “h,hh,hpp,hxx”. For header files without an extension, use an empty string (if there are no other desired extensions) or leave an empty element in the list. e.g., “h,hh,hpp,hxx,” (note the trailing comma).

UseHeaderFileExtension
    When non-zero, the check will use the file extension to distinguish header files. Default is 1.

  misc-fold-init-type

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 trucation wil 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);

  misc-forward-declaration-namespace

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.

  misc-inaccurate-erase

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.

  misc-incorrect-roundings

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.

  misc-inefficient-algorithm

Warns on inefficient use of STL algorithms on associative containers.

Associative containers implements some of the algorithms as methods which should be preferred to the algorithms in the algorithm header. The methods can take advanatage of the order of the elements.

  misc-macro-parentheses

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

Macros are expanded by the preprocessor as-is. As a result, there can be unexpected behaviour; 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.

  misc-macro-repeated-side-effects

Checks for repeated argument with side effects in macros.

  misc-misplaced-const

This check diagnoses when a const qualifier is applied to a typedef 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);

The check does not diagnose when the underlying typedef 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.

  misc-misplaced-widening-cast

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;
}

  Implicit casts

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;
}

  Floating point

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

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

  Options

CheckImplicitCasts
    If non-zero, enables detection of implicit casts. Default is non-zero.

  misc-move-const-arg

The check warns

•   if std::move() is called with a constant argument,

•   if std::move() is called with an argument of a trivially-copyable type,

•   if the result of std::move() is passed as a const reference argument.

    In all three cases, the check will suggest a fix that removes the std::move().

    Here are examples of each of the three cases:

    const string s;
    return std::move(s);  // Warning: std::move of the const variable has no effect
    int x;
    return std::move(x);  // Warning: std::move of the variable of a trivially-copyable type has no effect
    void f(const string &s);
    string s;
    f(std::move(s));  // Warning: passing result of std::move as a const reference argument; no move will actually happen

  misc-move-constructor-init

“cert-oop11-cpp” redirects here as an alias for this check.

The check flags user-defined move constructors that have a ctor-initializer initializing a member or base class through a copy constructor instead of a move constructor.

  Options

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

  misc-move-forwarding-reference

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));

  Background

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.

  misc-multiple-statement-macro

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.

  misc-new-delete-overloads

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.

  misc-noexcept-move-constructor

The check flags user-defined move constructors and assignment operators not marked with noexcept or marked with noexcept(expr) where expr evaluates to false (but is not a false literal itself).

Move constructors of all the types used with STL containers, for example, need to be declared noexcept. Otherwise STL will choose copy constructors instead. The same is valid for move assignment operations.

  misc-non-copyable-objects

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.

  misc-redundant-expression

Detect redundant expressions which are typically errors due to copy-paste.

Depending on the operator expressions may be

•   redundant,

•   always be true,

•   always be false,

•   always be a constant (zero or one).

    Example:

    ((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

  misc-sizeof-container

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.

  misc-sizeof-expression

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.

  Suspicious usage of ‘sizeof(K)’

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)

  Suspicious usage of ‘sizeof(this)’

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)
  [...]
};

  Suspicious usage of ‘sizeof(char*)’

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*)
}

  Suspicious usage of ‘sizeof(A*)’

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));

  Suspicious usage of ‘sizeof(…)/sizeof(…)’

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*]
}

  Suspicious ‘sizeof’ by ‘sizeof’ expression

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)
}

  Suspicious usage of ‘sizeof(sizeof(…))’

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.
}

  Options

WarnOnSizeOfConstant
    When non-zero, the check will warn on an expression like sizeof(CONSTANT). Default is 1.

WarnOnSizeOfThis
    When non-zero, the check will warn on an expression like sizeof(this). Default is 1.

WarnOnSizeOfCompareToConstant
    When non-zero, the check will warn on an expression like sizeof(epxr) <= k for a suspicious constant k while k is 0 or greater than 0x8000. Default is 1.

  misc-static-assert

cert-dcl03-c redirects here as an alias for this check.

Replaces assert() with static_assert() if the condition is evaluatable at compile time.

The condition of static_assert() is evaluated at compile time which is safer and more efficient.

  misc-string-compare

Finds string comparisons using the compare method.

A common mistake is to use the string’s compare method instead of using the equality or inequality operators. The compare method is intended for sorting functions and thus returns a negative number, a positive number or zero depending on the lexicographical relationship between the strings compared. If an equality or inequality check can suffice, that is recommended. This is recommended to avoid the risk of incorrect interpretation of the return value and to simplify the code. The string equality and inequality operators can also be faster than the compare method due to early termination.

Examples:

std::string str1{"a"};
std::string str2{"b"};
// use str1 != str2 instead.
if (str1.compare(str2)) {
}
// use str1 == str2 instead.
if (!str1.compare(str2)) {
}
// use str1 == str2 instead.
if (str1.compare(str2) == 0) {
}
// use str1 != str2 instead.
if (str1.compare(str2) != 0) {
}
// use str1 == str2 instead.
if (0 == str1.compare(str2)) {
}
// use str1 != str2 instead.
if (0 != str1.compare(str2)) {
}
// Use str1 == "foo" instead.
if (str1.compare("foo") == 0) {
}

The above code examples shows the list of if-statements that this check will give a warning for. All of them uses compare to check if equality or inequality of two strings instead of using the correct operators.

  misc-string-constructor

Finds string constructors that are suspicious and probably errors.

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

Examples:

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

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.

  Options

WarnOnLargeLength
    When non-zero, the check will warn on a string with a length greater than LargeLengthThreshold. Default is 1.

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

  misc-string-integer-assignment

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);

  misc-string-literal-with-embedded-nul

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

  Invalid escaping

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";

  Truncated literal

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

  misc-suspicious-enum-usage

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 intervalls 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.

  Options

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

  misc-suspicious-missing-comma

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",
};

  Options

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.

  misc-suspicious-semicolon

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.

  misc-suspicious-string-compare

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.

  Options

WarnOnImplicitComparison
    When non-zero, the check will warn on implicit comparison. 1 by default.

WarnOnLogicalNotComparison
    When non-zero, the check will warn on logical not comparison. 0 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.

  misc-swapped-arguments

Finds potentially swapped arguments by looking at implicit conversions.

  misc-throw-by-value-catch-by-reference

“cert-err09-cpp” redirects here as an alias for this check. “cert-err61-cpp” redirects here as an alias for 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.

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 idomatic.

•   Catching character pointers (char, wchar_t, unicode character types) will not be flagged to allow catching sting 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 flragged as not throwing an anonymous temporary. Although this can usually be done by just writing throw; it happens often enough in real code.

  Options

CheckThrowTemporaries
    Triggers detection of violations of the rule Throw anonymous temporaries. Default is 1.

  misc-unconventional-assign-operator

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&.

•   Works with move-assign and assign by value.

•   Private and deleted operators are ignored.

•   The operator must always return *this.

  misc-undelegated-constructor

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.

  misc-uniqueptr-reset-release

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>*.

  misc-unused-alias-decls

Finds unused namespace alias declarations.

  misc-unused-parameters

Finds unused parameters and fixes them, so that -Wunused-parameter can be turned on.

  misc-unused-raii

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.

  misc-unused-using-decls

Finds unused using declarations.

Example:

namespace n { class C; }
using n::C;  // Never actually used.

  misc-use-after-move

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;

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.

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;
}

Subsections below explain more precisely what exactly the check considers to be a move, use, and reinitialization.

  Unsequenced moves, uses, and reinitializations

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.

  Move

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.

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.

  Use

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.

  Reinitialization

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.

    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.

  misc-virtual-near-miss

Warn if a function is a near miss (ie. the name is very similar and the function signiture is the same) to a virtual function from a base class.

Example:

struct Base {
  virtual void func();
};
struct Derived : Base {
  virtual funk();
  // warning: 'Derived::funk' has a similar name and the same signature as virtual method 'Base::func'; did you mean to override it?
};

  modernize-avoid-bind

The check finds uses of std::bind and replaces simple uses with lambdas. Lambdas will use value-capture where required.

Right now it only handles free functions, not member functions.

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.

  modernize-deprecated-headers

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.

Improtant 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>

  modernize-loop-convert

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().

  MinConfidence option

  risky

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.

  reasonable (Default)

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];

  safe

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];

  Example

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 (int i = 0; i < v.size(); ++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;

  Limitations

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 behaviour and limitations of the check outlined by the cases below.

  Comments inside loop headers

Comments inside the original loop header are ignored and deleted when transformed.

for (int i = 0; i < N; /* This will be deleted */ ++i) { }

  Range-based loops evaluate end() only once

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();
}

  Overloaded operator->() with side effects

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->()
}

  Pointers and references to containers

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;
  }
}

  modernize-make-shared

This check finds the creation of std::shared_ptr objects by explicitly calling the constructor and a new expression, and replaces it with a call to std::make_shared.

auto my_ptr = std::shared_ptr<MyPair>(new MyPair(1, 2));
// becomes
auto my_ptr = std::make_shared<MyPair>(1, 2);

This check also finds calls to std::shared_ptr::reset() with a new expression, and replaces it with a call to std::make_shared.

my_ptr.reset(new MyPair(1, 2));
// becomes
my_ptr = std::make_shared<MyPair>(1, 2);

  modernize-make-unique

This check finds the creation of std::unique_ptr objects by explicitly calling the constructor and a new expression, and replaces it with a call to std::make_unique, introduced in C++14.

auto my_ptr = std::unique_ptr<MyPair>(new MyPair(1, 2));
// becomes
auto my_ptr = std::make_unique<MyPair>(1, 2);

This check also finds calls to std::unique_ptr::reset() with a new expression, and replaces it with a call to std::make_unique.

my_ptr.reset(new MyPair(1, 2));
// becomes
my_ptr = std::make_unique<MyPair>(1, 2);

  modernize-pass-by-value

With move semantics added to the language and the standard library updated with move constructors added for many types it is now interesting to take an argument directly by value, instead of by const-reference, and then copy. This check allows the compiler to take care of choosing the best way to construct the copy.

The transformation is usually beneficial when the calling code passes an rvalue and assumes the move construction is a cheap operation. This short example illustrates how the construction of the value happens:

void foo(std::string s);
std::string get_str();
void f(const std::string &str) {
  foo(str);       // lvalue  -> copy construction
  foo(get_str()); // prvalue -> move construction
}

NOTE: Currently, only constructors are transformed to make use of pass-by-value. Contributions that handle other situations are welcome!

  Pass-by-value in constructors

Replaces the uses of const-references constructor parameters that are copied into class fields. The parameter is then moved with std::move().

Since std::move() is a library function declared in <utility> it may be necessary to add this include. The check will add the include directive when necessary.

 #include <string>
 class Foo {
 public:
-  Foo(const std::string &Copied, const std::string &ReadOnly)
-    : Copied(Copied), ReadOnly(ReadOnly)
+  Foo(std::string Copied, const std::string &ReadOnly)
+    : Copied(std::move(Copied)), ReadOnly(ReadOnly)
   {}
 private:
   std::string Copied;
   const std::string &ReadOnly;
 };
 std::string get_cwd();
 void f(const std::string &Path) {
   // The parameter corresponding to 'get_cwd()' is move-constructed. By
   // using pass-by-value in the Foo constructor we managed to avoid a
   // copy-construction.
   Foo foo(get_cwd(), Path);
 }

If the parameter is used more than once no transformation is performed since moved objects have an undefined state. It means the following code will be left untouched:

#include <string>
void pass(const std::string &S);
struct Foo {
  Foo(const std::string &S) : Str(S) {
    pass(S);
  }
  std::string Str;
};

  Known limitations

A situation where the generated code can be wrong is when the object referenced is modified before the assignment in the init-list through a “hidden” reference.

Example:

 std::string s("foo");
 struct Base {
   Base() {
     s = "bar";
   }
 };
 struct Derived : Base {
-  Derived(const std::string &S) : Field(S)
+  Derived(std::string S) : Field(std::move(S))
   { }
   std::string Field;
 };
 void f() {
-  Derived d(s); // d.Field holds "bar"
+  Derived d(s); // d.Field holds "foo"
 }

  Note about delayed template parsing

When delayed template parsing is enabled, constructors part of templated contexts; templated constructors, constructors in class templates, constructors of inner classes of template classes, etc., are not transformed. Delayed template parsing is enabled by default on Windows as a Microsoft extension: Clang Compiler User’s Manual - Microsoft extensions.

Delayed template parsing can be enabled using the -fdelayed-template-parsing flag and disabled using -fno-delayed-template-parsing.

Example:

  template <typename T> class C {
    std::string S;
  public:
=  // using -fdelayed-template-parsing (default on Windows)
=  C(const std::string &S) : S(S) {}
+  // using -fno-delayed-template-parsing (default on non-Windows systems)
+  C(std::string S) : S(std::move(S)) {}
  };

SEE ALSO: For more information about the pass-by-value idiom, read: Want Speed? Pass by Value.

  Options

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

ValuesOnly
    When non-zero, the check only warns about copied parameters that are already passed by value. Default is 0.

  modernize-raw-string-literal

This check selectively replaces string literals containing escaped characters with raw string literals.

Example:

const char *const Quotes{"embedded \"quotes\""};
const char *const Paragraph{"Line one.\nLine two.\nLine three.\n"};
const char *const SingleLine{"Single line.\n"};
const char *const TrailingSpace{"Look here -> \n"};
const char *const Tab{"One\tTwo\n"};
const char *const Bell{"Hello!\a  And welcome!"};
const char *const Path{"C:\\Program Files\\Vendor\\Application.exe"};
const char *const RegEx{"\\w\\([a-z]\\)"};

becomes

const char *const Quotes{R"(embedded "quotes")"};
const char *const Paragraph{"Line one.\nLine two.\nLine three.\n"};
const char *const SingleLine{"Single line.\n"};
const char *const TrailingSpace{"Look here -> \n"};
const char *const Tab{"One\tTwo\n"};
const char *const Bell{"Hello!\a  And welcome!"};
const char *const Path{R"(C:\Program Files\Vendor\Application.exe)"};
const char *const RegEx{R"(\w\([a-z]\))"};

The presence of any of the following escapes can cause the string to be converted to a raw string literal: \\, \', \", \?, and octal or hexadecimal escapes for printable ASCII characters.

A string literal containing only escaped newlines is a common way of writing lines of text output. Introducing physical newlines with raw string literals in this case is likely to impede readability. These string literals are left unchanged.

An escaped horizontal tab, form feed, or vertical tab prevents the string literal from being converted. The presence of a horizontal tab, form feed or vertical tab in source code is not visually obvious.

  modernize-redundant-void-arg

Find and remove redundant void argument lists.

Examples:
    Initial code | Code with applied fixes
    int f(void); | int f();
    int (*f(void))(void); | int (*f())();
    typedef int (*f_t(void))(void); | typedef int (*f_t())();
    void (C::*p)(void); | void (C::*p)();
    C::C(void) {} | C::C() {}
    C::~C(void) {} | C::~C() {}

  modernize-replace-auto-ptr

This check replaces the uses of the deprecated class std::auto_ptr by std::unique_ptr (introduced in C++11). The transfer of ownership, done by the copy-constructor and the assignment operator, is changed to match std::unique_ptr usage by using explicit calls to std::move().

Migration example:

-void take_ownership_fn(std::auto_ptr<int> int_ptr);
+void take_ownership_fn(std::unique_ptr<int> int_ptr);
 void f(int x) {
-  std::auto_ptr<int> a(new int(x));
-  std::auto_ptr<int> b;
+  std::unique_ptr<int> a(new int(x));
+  std::unique_ptr<int> b;
-  b = a;
-  take_ownership_fn(b);
+  b = std::move(a);
+  take_ownership_fn(std::move(b));
 }

Since std::move() is a library function declared in <utility> it may be necessary to add this include. The check will add the include directive when necessary.

  Known Limitations

•   If headers modification is not activated or if a header is not allowed to be changed this check will produce broken code (compilation error), where the headers’ code will stay unchanged while the code using them will be changed.

•   Client code that declares a reference to an std::auto_ptr coming from code that can’t be migrated (such as a header coming from a 3rd party library) will produce a compilation error after migration. This is because the type of the reference will be changed to std::unique_ptr but the type returned by the library won’t change, binding a reference to std::unique_ptr from an std::auto_ptr. This pattern doesn’t make much sense and usually std::auto_ptr are stored by value (otherwise what is the point in using them instead of a reference or a pointer?).

     // <3rd-party header...>
     std::auto_ptr<int> get_value();
     const std::auto_ptr<int> & get_ref();
     // <calling code (with migration)...>
    -std::auto_ptr<int> a(get_value());
    +std::unique_ptr<int> a(get_value()); // ok, unique_ptr constructed from auto_ptr
    -const std::auto_ptr<int> & p = get_ptr();
    +const std::unique_ptr<int> & p = get_ptr(); // won't compile

•   Non-instantiated templates aren’t modified.

    template <typename X>
    void f() {
        std::auto_ptr<X> p;
    }
    // only 'f<int>()' (or similar) will trigger the replacement.

  Options

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

  modernize-shrink-to-fit

Replace copy and swap tricks on shrinkable containers with the shrink_to_fit() method call.

The shrink_to_fit() method is more readable and more effective than the copy and swap trick to reduce the capacity of a shrinkable container. Note that, the shrink_to_fit() method is only available in C++11 and up.

  modernize-use-auto

This check is responsible for using the auto type specifier for variable declarations to improve code readability and maintainability. For example:

std::vector<int>::iterator I = my_container.begin();
// transforms to:
auto I = my_container.begin();

The auto type specifier will only be introduced in situations where the variable type matches the type of the initializer expression. In other words auto should deduce the same type that was originally spelled in the source. However, not every situation should be transformed:

int val = 42;
InfoStruct &I = SomeObject.getInfo();
// Should not become:
auto val = 42;
auto &I = SomeObject.getInfo();

In this example using auto for builtins doesn’t improve readability. In other situations it makes the code less self-documenting impairing readability and maintainability. As a result, auto is used only introduced in specific situations described below.

  Iterators

Iterator type specifiers tend to be long and used frequently, especially in loop constructs. Since the functions generating iterators have a common format, the type specifier can be replaced without obscuring the meaning of code while improving readability and maintainability.

for (std::vector<int>::iterator I = my_container.begin(),
                                E = my_container.end();
     I != E; ++I) {
}
// becomes
for (auto I = my_container.begin(), E = my_container.end(); I != E; ++I) {
}

The check will only replace iterator type-specifiers when all of the following conditions are satisfied:

•   The iterator is for one of the standard container in std namespace:

•   array

•   deque

•   forward_list

•   list

•   vector

•   map

•   multimap

•   set

•   multiset

•   unordered_map

•   unordered_multimap

•   unordered_set

•   unordered_multiset

•   queue

•   priority_queue

•   stack

•   The iterator is one of the possible iterator types for standard containers:

•   iterator

•   reverse_iterator

•   const_iterator

•   const_reverse_iterator

•   In addition to using iterator types directly, typedefs or other ways of referring to those types are also allowed. However, implementation-specific types for which a type like std::vector<int>::iterator is itself a typedef will not be transformed. Consider the following examples:

    // The following direct uses of iterator types will be transformed.
    std::vector<int>::iterator I = MyVec.begin();
    {
      using namespace std;
      list<int>::iterator I = MyList.begin();
    }
    // The type specifier for J would transform to auto since it's a typedef
    // to a standard iterator type.
    typedef std::map<int, std::string>::const_iterator map_iterator;
    map_iterator J = MyMap.begin();
    // The following implementation-specific iterator type for which
    // std::vector<int>::iterator could be a typedef would not be transformed.
    __gnu_cxx::__normal_iterator<int*, std::vector> K = MyVec.begin();

•   The initializer for the variable being declared is not a braced initializer list. Otherwise, use of auto would cause the type of the variable to be deduced as std::initializer_list.

  New expressions

Frequently, when a pointer is declared and initialized with new, the pointee type is written twice: in the declaration type and in the new expression. In this cases, the declaration type can be replaced with auto improving readability and maintainability.

TypeName *my_pointer = new TypeName(my_param);
// becomes
auto *my_pointer = new TypeName(my_param);

The check will also replace the declaration type in multiple declarations, if the following conditions are satisfied:

•   All declared variables have the same type (i.e. all of them are pointers to the same type).

•   All declared variables are initialized with a new expression.

•   The types of all the new expressions are the same than the pointee of the declaration type.

    TypeName *my_first_pointer = new TypeName, *my_second_pointer = new TypeName;
    // becomes
    auto *my_first_pointer = new TypeName, *my_second_pointer = new TypeName;

  Cast expressions

Frequently, when a variable is declared and initialized with a cast, the variable type is written twice: in the declaration type and in the cast expression. In this cases, the declaration type can be replaced with auto improving readability and maintainability.

TypeName *my_pointer = static_cast<TypeName>(my_param);
// becomes
auto *my_pointer = static_cast<TypeName>(my_param);

The check handles static_cast, dynamic_cast, const_cast, reinterpret_cast, functional casts, C-style casts and function templates that behave as casts, such as llvm::dyn_cast, boost::lexical_cast and gsl::narrow_cast. Calls to function templates are considered to behave as casts if the first template argument is explicit and is a type, and the function returns that type, or a pointer or reference to it.

  Known Limitations

•   If the initializer is an explicit conversion constructor, the check will not replace the type specifier even though it would be safe to do so.

•   User-defined iterators are not handled at this time.

  Options

RemoveStars
    If the option is set to non-zero (default is 0), the check will remove stars from the non-typedef pointer types when replacing type names with auto. Otherwise, the check will leave stars. For example:

    TypeName *my_first_pointer = new TypeName, *my_second_pointer = new TypeName;
    // RemoveStars = 0
    auto *my_first_pointer = new TypeName, *my_second_pointer = new TypeName;
    // RemoveStars = 1
    auto my_first_pointer = new TypeName, my_second_pointer = new TypeName;

  modernize-use-bool-literals

Finds integer literals which are cast to bool.

bool p = 1;
bool f = static_cast<bool>(1);
std::ios_base::sync_with_stdio(0);
bool x = p ? 1 : 0;
// transforms to
bool p = true;
bool f = true;
std::ios_base::sync_with_stdio(false);
bool x = p ? true : false;

  modernize-use-default-member-init

This check converts a default constructor’s member initializers into the new default member initializers in C++11. Other member initializers that match the default member initializer are removed. This can reduce repeated code or allow use of ‘= default’.

struct A {
  A() : i(5), j(10.0) {}
  A(int i) : i(i), j(10.0) {}
  int i;
  double j;
};
// becomes
struct A {
  A() {}
  A(int i) : i(i) {}
  int i{5};
  double j{10.0};
};

NOTE: Only converts member initializers for built-in types, enums, and pointers. The readability-redundant-member-init check will remove redundant member initializers for classes.

  Options

UseAssignment
    If this option is set to non-zero (default is 0), the check will initialise members with an assignment. For example:

    struct A {
      A() {}
      A(int i) : i(i) {}
      int i = 5;
      double j = 10.0;
    };

  modernize-use-emplace

The check flags insertions to an STL-style container done by calling the push_back method with an explicitly-constructed temporary of the container element type. In this case, the corresponding emplace_back method results in less verbose and potentially more efficient code. Right now the check doesn’t support push_front and insert. It also doesn’t support insert functions for associative containers because replacing insert with emplace may result in speed regression, but it might get support with some addition flag in the future.

By default only std::vector, std::deque, std::list are considered. This list can be modified using the ContainersWithPushBack option.

Before:

std::vector<MyClass> v;
v.push_back(MyClass(21, 37));
std::vector<std::pair<int, int>> w;
w.push_back(std::pair<int, int>(21, 37));
w.push_back(std::make_pair(21L, 37L));

After:

std::vector<MyClass> v;
v.emplace_back(21, 37);
std::vector<std::pair<int, int>> w;
w.emplace_back(21, 37);
// This will be fixed to w.push_back(21, 37); in next version
w.emplace_back(std::make_pair(21L, 37L);

The other situation is when we pass arguments that will be converted to a type inside a container.

Before:

std::vector<boost::optional<std::string> > v;
v.push_back("abc");

After:

std::vector<boost::optional<std::string> > v;
v.emplace_back("abc");

In some cases the transformation would be valid, but the code wouldn’t be exception safe. In this case the calls of push_back won’t be replaced.

std::vector<std::unique_ptr<int>> v;
v.push_back(std::unique_ptr<int>(new int(0)));
auto *ptr = new int(1);
v.push_back(std::unique_ptr<int>(ptr));

This is because replacing it with emplace_back could cause a leak of this pointer if emplace_back would throw exception before emplacement (e.g. not enough memory to add new element).

For more info read item 42 - “Consider emplacement instead of insertion.” of Scott Meyers “Effective Modern C++”.

The default smart pointers that are considered are std::unique_ptr, std::shared_ptr, std::auto_ptr. To specify other smart pointers or other classes use the SmartPointers option.

Check also fires if any argument of constructor call would be:

•   bitfield (bitfields can’t bind to rvalue/universal reference)

•   new expression (to avoid leak) or if the argument would be converted via derived-to-base cast.

    This check requires C++11 of higher to run.

  Options

ContainersWithPushBack
    Semicolon-separated list of class names of custom containers that support push_back.

SmartPointers
    Semicolon-separated list of class names of custom smart pointers.

  modernize-use-equals-default

This check replaces default bodies of special member functions with = default;. The explicitly defaulted function declarations enable more opportunities in optimization, because the compiler might treat explicitly defaulted functions as trivial.

struct A {
  A() {}
  ~A();
};
A::~A() {}
// becomes
struct A {
  A() = default;
  ~A();
};
A::~A() = default;

NOTE: Move-constructor and move-assignment operator are not supported yet.

  modernize-use-equals-delete

This check marks unimplemented private special member functions with = delete. To avoid false-positives, this check only applies in a translation unit that has all other member functions implemented.

struct A {
private:
  A(const A&);
  A& operator=(const A&);
};
// becomes
struct A {
private:
  A(const A&) = delete;
  A& operator=(const A&) = delete;
};

  modernize-use-nullptr

The check converts the usage of null pointer constants (eg. NULL, 0) to use the new C++11 nullptr keyword.

  Example

void assignment() {
  char *a = NULL;
  char *b = 0;
  char c = 0;
}
int *ret_ptr() {
  return 0;
}

transforms to:

void assignment() {
  char *a = nullptr;
  char *b = nullptr;
  char c = 0;
}
int *ret_ptr() {
  return nullptr;
}

  Options

UserNullMacros
    Comma-separated list of macro names that will be transformed along with NULL. By default this check will only replace the NULL macro and will skip any similar user-defined macros.

  Example

#define MY_NULL (void*)0
void assignment() {
  void *p = MY_NULL;
}

transforms to:

#define MY_NULL NULL
void assignment() {
  int *p = nullptr;
}

if the UserNullMacros option is set to MY_NULL.

  modernize-use-override

Use C++11’s override and remove virtual where applicable.

  modernize-use-transparent-functors

Prefer transparent functors to non-transparent ones. When using transparent functors, the type does not need to be repeated. The code is easier to read, maintain and less prone to errors. It is not possible to introduce unwanted conversions.

// Non-transparent functor
std::map<int, std::string, std::greater<int>> s;
// Transparent functor.
std::map<int, std::string, std::greater<>> s;
// Non-transparent functor
using MyFunctor = std::less<MyType>;

It is not always a safe transformation though. The following case will be untouched to preserve the semantics.

// Non-transparent functor
std::map<const char *, std::string, std::greater<std::string>> s;

  Options

SafeMode
    If the option is set to non-zero, the check will not diagnose cases where using a transparent functor cannot be guaranteed to produce identical results as the original code. The default value for this option is 0.

    This check requires using C++14 or higher to run.

  modernize-use-using

The check converts the usage of typedef with using keyword.

Before:

typedef int variable;
class Class{};
typedef void (Class::* MyPtrType)() const;

After:

using variable = int;
class Class{};
using MyPtrType = void (Class::*)() const;

This check requires using C++11 or higher to run.

  mpi-buffer-deref

This check verifies if a buffer passed to an MPI (Message Passing Interface) function is sufficiently dereferenced. Buffers should be passed as a single pointer or array. As MPI function signatures specify void * for their buffer types, insufficiently dereferenced buffers can be passed, like for example as double pointers or multidimensional arrays, without a compiler warning emitted.

Examples:

// A double pointer is passed to the MPI function.
char *buf;
MPI_Send(&buf, 1, MPI_CHAR, 0, 0, MPI_COMM_WORLD);
// A multidimensional array is passed to the MPI function.
short buf[1][1];
MPI_Send(buf, 1, MPI_SHORT, 0, 0, MPI_COMM_WORLD);
// A pointer to an array is passed to the MPI function.
short *buf[1];
MPI_Send(buf, 1, MPI_SHORT, 0, 0, MPI_COMM_WORLD);

  mpi-type-mismatch

This check verifies if buffer type and MPI (Message Passing Interface) datatype pairs match for used MPI functions. All MPI datatypes defined by the MPI standard (3.1) are verified by this check. User defined typedefs, custom MPI datatypes and null pointer constants are skipped, in the course of verification.

Example:

// In this case, the buffer type matches MPI datatype.
char buf;
MPI_Send(&buf, 1, MPI_CHAR, 0, 0, MPI_COMM_WORLD);
// In the following case, the buffer type does not match MPI datatype.
int buf;
MPI_Send(&buf, 1, MPI_CHAR, 0, 0, MPI_COMM_WORLD);

  performance-faster-string-find

Optimize calls to std::string::find() and friends when the needle passed is a single character string literal. The character literal overload is more efficient.

Examples:

str.find("A");
// becomes
str.find('A');

  Options

StringLikeClasses
    Semicolon-separated list of names of string-like classes. By default only std::basic_string is considered. The list of methods to consired is fixed.

  performance-for-range-copy

Finds C++11 for ranges where the loop variable is copied in each iteration but it would suffice to obtain it by const reference.

The check is only applied to loop variables of types that are expensive to copy which means they are not trivially copyable or have a non-trivial copy constructor or destructor.

To ensure that it is safe to replace the copy with a const reference the following heuristic is employed:

1.  The loop variable is const qualified.

2.  The loop variable is not const, but only const methods or operators are invoked on it, or it is used as const reference or value argument in constructors or function calls.

  Options

WarnOnAllAutoCopies
    When non-zero, warns on any use of auto as the type of the range-based for loop variable. Default is 0.

  performance-implicit-cast-in-loop

This warning appears in a range-based loop with a loop variable of const ref type where the type of the variable does not match the one returned by the iterator. This means that an implicit cast has been added, which can for example result in expensive deep copies.

Example:

map<int, vector<string>> my_map;
for (const pair<int, vector<string>>& p : my_map) {}
// The iterator type is in fact pair<const int, vector<string>>, which means
// that the compiler added a cast, resulting in a copy of the vectors.

The easiest solution is usually to use const auto& instead of writing the type manually.

  performance-inefficient-string-concatenation

This check warns about the performance overhead arising from concatenating strings using the operator+, for instance:

std::string a("Foo"), b("Bar");
a = a + b;

Instead of this structure you should use operator+= or std::string’s (std::basic_string) class member function append(). For instance:

std::string a("Foo"), b("Baz");
for (int i = 0; i < 20000; ++i) {
    a = a + "Bar" + b;
}

Could be rewritten in a greatly more efficient way like:

std::string a("Foo"), b("Baz");
for (int i = 0; i < 20000; ++i) {
    a.append("Bar").append(b);
}

And this can be rewritten too:

void f(const std::string&) {}
std::string a("Foo"), b("Baz");
void g() {
    f(a + "Bar" + b);
}

In a slightly more efficient way like:

void f(const std::string&) {}
std::string a("Foo"), b("Baz");
void g() {
    f(std::string(a).append("Bar").append(b));
}

  Options

StrictMode
    When zero, the check will only check the string usage in while, for and for-range statements. Default is 0.

  performance-type-promotion-in-math-fn

Finds calls to C math library functions (from math.h or, in C++, cmath) with implicit float to double promotions.

For example, warns on ::sin(0.f), because this funciton’s parameter is a double. You probably meant to call std::sin(0.f) (in C++), or sinf(0.f) (in C).

  performance-unnecessary-copy-initialization

Finds local variable declarations that are initialized using the copy constructor of a non-trivially-copyable type but it would suffice to obtain a const reference.

The check is only applied if it is safe to replace the copy by a const reference. This is the case when the variable is const qualified or when it is only used as a const, i.e. only const methods or operators are invoked on it, or it is used as const reference or value argument in constructors or function calls.

Example:

const string& constReference();
void Function() {
  // The warning will suggest making this a const reference.
  const string UnnecessaryCopy = constReference();
}
struct Foo {
  const string& name() const;
};
void Function(const Foo& foo) {
  // The warning will suggest making this a const reference.
  string UnnecessaryCopy1 = foo.name();
  UnnecessaryCopy1.find("bar");
  // The warning will suggest making this a const reference.
  string UnnecessaryCopy2 = UnnecessaryCopy1;
  UnnecessaryCopy2.find("bar");
}

  performance-unnecessary-value-param

Flags value parameter declarations of expensive to copy types that are copied for each invocation but it would suffice to pass them by const reference.

The check is only applied to parameters of types that are expensive to copy which means they are not trivially copyable or have a non-trivial copy constructor or destructor.

To ensure that it is safe to replace the value parameter with a const reference the following heuristic is employed:

1.  the parameter is const qualified;

2.  the parameter is not const, but only const methods or operators are invoked on it, or it is used as const reference or value argument in constructors or function calls.

    Example:

    void f(const string Value) {
      // The warning will suggest making Value a reference.
    }
    void g(ExpensiveToCopy Value) {
      // The warning will suggest making Value a const reference.
      Value.ConstMethd();
      ExpensiveToCopy Copy(Value);
    }

    If the parameter is not const, only copied or assigned once and has a non-trivial move-constructor or move-assignment operator respectively the check will suggest to move it.

    Example:

    void setValue(string Value) {
      Field = Value;
    }

    Will become:

    #include <utility>
    void setValue(string Value) {
      Field = std::move(Value);
    }

  Options

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

  readability-avoid-const-params-in-decls

Checks whether a function declaration has parameters that are top level const.

const values in declarations do not affect the signature of a function, so they should not be put there.

Examples:

void f(const string);   // Bad: const is top level.
void f(const string&);  // Good: const is not top level.

  readability-braces-around-statements

google-readability-braces-around-statements redirects here as an alias for this check.

Checks that bodies of if statements and loops (for, do while, and while) are inside braces.

Before:

if (condition)
  statement;

After:

if (condition) {
  statement;
}

  Options

ShortStatementLines
    Defines the minimal number of lines that the statement should have in order to trigger this check.

    The number of lines is counted from the end of condition or initial keyword (do/else) until the last line of the inner statement. Default value 0 means that braces will be added to all statements (not having them already).

  readability-container-size-empty

Checks whether a call to the size() method can be replaced with a call to empty().

The emptiness of a container should be checked using the empty() method instead of the size() method. It is not guaranteed that size() is a constant-time function, and it is generally more efficient and also shows clearer intent to use empty(). Furthermore some containers may implement the empty() method but not implement the size() method. Using empty() whenever possible makes it easier to switch to another container in the future.

The check issues warning if a container has size() and empty() methods matching following signatures:

code-block:: c++ size_type size() const; bool empty() const;

size_type can be any kind of integer type.

  readability-delete-null-pointer

Checks the if statements where a pointer’s existence is checked and then deletes the pointer. The check is unnecessary as deleting a null pointer has no effect.

int *p;
if (p)
  delete p;

  readability-deleted-default

Checks that constructors and assignment operators marked as = default are not actually deleted by the compiler.

class Example {
public:
  // This constructor is deleted because I is missing a default value.
  Example() = default;
  // This is fine.
  Example(const Example& Other) = default;
  // This operator is deleted because I cannot be assigned (it is const).
  Example& operator=(const Example& Other) = default;
private:
  const int I;
};

  readability-else-after-return

LLVM Coding Standards advises to reduce indentation where possible and where it makes understanding code easier. Early exit is one of the suggested enforcements of that. Please do not use else or else if after something that interrupts control flow - like return, break, continue, throw.

The following piece of code illustrates how the check works. This piece of code:

void foo(int Value) {
  int Local = 0;
  for (int i = 0; i < 42; i++) {
    if (Value == 1) {
      return;
    } else {
      Local++;
    }
    if (Value == 2)
      continue;
    else
      Local++;
    if (Value == 3) {
      throw 42;
    } else {
      Local++;
    }
  }
}

Would be transformed into:

void foo(int Value) {
  int Local = 0;
  for (int i = 0; i < 42; i++) {
    if (Value == 1) {
      return;
    }
    Local++;
    if (Value == 2)
      continue;
    Local++;
    if (Value == 3) {
      throw 42;
    }
    Local++;
  }
}

This check helps to enforce this LLVM Coding Standards recommendation.

  readability-function-size

google-readability-function-size redirects here as an alias for this check.

Checks for large functions based on various metrics.

  Options

LineThreshold
    Flag functions exceeding this number of lines. The default is -1 (ignore the number of lines).

StatementThreshold
    Flag functions exceeding this number of statements. This may differ significantly from the number of lines for macro-heavy code. The default is 800.

BranchThreshold
    Flag functions exceeding this number of control statements. The default is -1 (ignore the number of branches).

  readability-identifier-naming

Checks for identifiers naming style mismatch.

This check will try to enforce coding guidelines on the identifiers naming. It supports lower_case, UPPER_CASE, camelBack and CamelCase casing and tries to convert from one to another if a mismatch is detected.

It also supports a fixed prefix and suffix that will be prepended or appended to the identifiers, regardless of the casing.

Many configuration options are available, in order to be able to create different rules for different kind of identifier. In general, the rules are falling back to a more generic rule if the specific case is not configured.

  readability-implicit-bool-cast

This check can be used to find implicit conversions between built-in types and booleans. Depending on use case, it may simply help with readability of the code, or in some cases, point to potential bugs which remain unnoticed due to implicit conversions.

The following is a real-world example of bug which was hiding behind implicit bool cast:

class Foo {
  int m_foo;
public:
  void setFoo(bool foo) { m_foo = foo; } // warning: implicit cast bool -> int
  int getFoo() { return m_foo; }
};
void use(Foo& foo) {
  bool value = foo.getFoo(); // warning: implicit cast int -> bool
}

This code is the result of unsuccessful refactoring, where type of m_foo changed from bool to int. The programmer forgot to change all occurrences of bool, and the remaining code is no longer correct, yet it still compiles without any visible warnings.

In addition to issuing warnings, fix-it hints are provided to help solve the reported issues. This can be used for improving readability of code, for example:

void conversionsToBool() {
  float floating;
  bool boolean = floating;
  // ^ propose replacement: bool boolean = floating != 0.0f;
  int integer;
  if (integer) {}
  // ^ propose replacement: if (integer != 0) {}
  int* pointer;
  if (!pointer) {}
  // ^ propose replacement: if (pointer == nullptr) {}
  while (1) {}
  // ^ propose replacement: while (true) {}
}
void functionTakingInt(int param);
void conversionsFromBool() {
  bool boolean;
  functionTakingInt(boolean);
  // ^ propose replacement: functionTakingInt(static_cast<int>(boolean));
  functionTakingInt(true);
  // ^ propose replacement: functionTakingInt(1);
}

In general, the following cast types are checked:

•   integer expression/literal to boolean,

•   floating expression/literal to boolean,

•   pointer/pointer to member/nullptr/NULL to boolean,

•   boolean expression/literal to integer,

•   boolean expression/literal to floating.

    The rules for generating fix-it hints are:

•   in case of casts from other built-in type to bool, an explicit comparison is proposed to make it clear what exaclty is being compared:

•   bool boolean = floating; is changed to bool boolean = floating == 0.0f;,

•   for other types, appropriate literals are used (0, 0u, 0.0f, 0.0, nullptr),

•   in case of negated expressions cast to bool, the proposed replacement with comparison is simplified:

•   if (!pointer) is changed to if (pointer == nullptr),

•   in case of casts from bool to other built-in types, an explicit static_cast is proposed to make it clear that a cast is taking place:

•   int integer = boolean; is changed to int integer = static_cast<int>(boolean);,

•   if the cast is performed on type literals, an equivalent literal is proposed, according to what type is actually expected, for example:

•   functionTakingBool(0); is changed to functionTakingBool(false);,

•   functionTakingInt(true); is changed to functionTakingInt(1);,

•   for other types, appropriate literals are used (false, true, 0, 1, 0u, 1u, 0.0f, 1.0f, 0.0, 1.0f).

    Some additional accommodations are made for pre-C++11 dialects:

•   false literal cast to pointer is detected,

•   instead of nullptr literal, 0 is proposed as replacement.

    Occurrences of implicit casts inside macros and template instantiations are deliberately ignored, as it is not clear how to deal with such cases.

  Options

AllowConditionalIntegerCasts
    When non-zero, the check will allow conditional integer casts. Default is 0.

AllowConditionalPointerCasts
    When non-zero, the check will allow conditional pointer casts. Default is 0.

  readability-inconsistent-declaration-parameter-name

Find function declarations which differ in parameter names.

Example:

// in foo.hpp:
void foo(int a, int b, int c);
// in foo.cpp:
void foo(int d, int e, int f); // warning

This check should help to enforce consistency in large projects, where it often happens that a definition of function is refactored, changing the parameter names, but its declaration in header file is not updated. With this check, we can easily find and correct such inconsistencies, keeping declaration and definition always in sync.

Unnamed parameters are allowed and are not taken into account when comparing function declarations, for example:

void foo(int a);
void foo(int); // no warning

To help with refactoring, in some cases fix-it hints are generated to align parameter names to a single naming convention. This works with the assumption that the function definition is the most up-to-date version, as it directly references parameter names in its body. Example:

void foo(int a); // warning and fix-it hint (replace "a" to "b")
int foo(int b) { return b + 2; } // definition with use of "b"

In the case of multiple redeclarations or function template specializations, a warning is issued for every redeclaration or specialization inconsistent with the definition or the first declaration seen in a translation unit.

  readability-misplaced-array-index

This check warns for unusual array index syntax.

The following code has unusual array index syntax:

void f(int *X, int Y) {
  Y[X] = 0;
}

becomes

void f(int *X, int Y) {
  X[Y] = 0;
}

The check warns about such unusual syntax for readability reasons:

•   There are programmers that are not familiar with this unusual syntax.

•   It is possible that variables are mixed up.

  readability-named-parameter

Find functions with unnamed arguments.

The check implements the following rule originating in the Google C++ Style Guide:

https://google.github.io/styleguide/cppguide.html#Function_Declarations_and_Definitions

All parameters should be named, with identical names in the declaration and implementation.

Corresponding cpplint.py check name: readability/function.

  readability-non-const-parameter

The check finds function parameters of a pointer type that could be changed to point to a constant type instead.

When const is used properly, many mistakes can be avoided. Advantages when using const properly:

•   prevent unintentional modification of data;

•   get additional warnings such as using uninitialized data;

•   make it easier for developers to see possible side effects.

    This check is not strict about constness, it only warns when the constness will make the function interface safer.

    // warning here; the declaration "const char *p" would make the function
    // interface safer.
    char f1(char *p) {
      return *p;
    }
    // no warning; the declaration could be more const "const int * const p" but
    // that does not make the function interface safer.
    int f2(const int *p) {
      return *p;
    }
    // no warning; making x const does not make the function interface safer
    int f3(int x) {
      return x;
    }
    // no warning; Technically, *p can be const ("const struct S *p"). But making
    // *p const could be misleading. People might think that it's safe to pass
    // const data to this function.
    struct S { int *a; int *b; };
    int f3(struct S *p) {
      *(p->a) = 0;
    }

  readability-redundant-control-flow

This check looks for procedures (functions returning no value) with return statements at the end of the function. Such return statements are redundant.

Loop statements (for, while, do while) are checked for redundant continue statements at the end of the loop body.

Examples:

The following function f contains a redundant return statement:

extern void g();
void f() {
  g();
  return;
}

becomes

extern void g();
void f() {
  g();
}

The following function k contains a redundant continue statement:

void k() {
  for (int i = 0; i < 10; ++i) {
    continue;
  }
}

becomes

void k() {
  for (int i = 0; i < 10; ++i) {
  }
}

  readability-redundant-declaration

Finds redundant variable and function declarations.

extern int X;
extern int X;

becomes

extern int X;

Such redundant declarations can be removed without changing program behaviour. They can for instance be unintentional left overs from previous refactorings when code has been moved around. Having redundant declarations could in worst case mean that there are typos in the code that cause bugs.

Normally the code can be automatically fixed, clang-tidy can remove the second declaration. However there are 2 cases when you need to fix the code manually:

•   When the declarations are in different header files;

•   When multiple variables are declared together.

  readability-redundant-function-ptr-dereference

Finds redundant dereferences of a function pointer.

Before:

int f(int,int);
int (*p)(int, int) = &f;
int i = (**p)(10, 50);

After:

int f(int,int);
int (*p)(int, int) = &f;
int i = (*p)(10, 50);

  readability-redundant-member-init

Finds member initializations that are unnecessary because the same default constructor would be called if they were not present.

Example:

// Explicitly initializing the member s is unnecessary.
class Foo {
public:
  Foo() : s() {}
private:
  std::string s;
};

  readability-redundant-smartptr-get

google-readability-redundant-smartptr-get redirects here as an alias for this check.

Find and remove redundant calls to smart pointer’s .get() method.

Examples:

ptr.get()->Foo()  ==>  ptr->Foo()
*ptr.get()  ==>  *ptr
*ptr->get()  ==>  **ptr

  readability-redundant-string-cstr

Finds unnecessary calls to std::string::c_str() and std::string::data().

  readability-redundant-string-init

Finds unnecessary string initializations.

Examples:

// Initializing string with empty string literal is unnecessary.
std::string a = "";
std::string b("");

  readability-simplify-boolean-expr

Looks for boolean expressions involving boolean constants and simplifies them to use the appropriate boolean expression directly.

Examples:
Initial expression | Result
if (b == true) | if (b)
if (b == false) | if (!b)
if (b && true) | if (b)
if (b && false) | if (false)
if (b || true) | if (true)
if (b || false) | if (b)
e ? true : false | e
e ? false : true | !e
if (true) t(); else f(); | t();
if (false) t(); else f(); | f();
if (e) return true; else return false; | return e;
if (e) return false; else return true; | return !e;
if (e) b = true; else b = false; | b = e;
if (e) b = false; else b = true; | b = !e;
if (e) return true; return false; | return e;
if (e) return false; return true; | return !e;

The resulting expression e is modified as follows:

1.  Unnecessary parentheses around the expression are removed.

2.  Negated applications of ! are eliminated.

3.  Negated applications of comparison operators are changed to use the opposite condition.

4.  Implicit conversions of pointers, including pointers to members, to bool are replaced with explicit comparisons to nullptr in C++11 or NULL in C++98/03.

5.  Implicit casts to bool are replaced with explicit casts to bool.

6.  Object expressions with explicit operator bool conversion operators are replaced with explicit casts to bool.

7.  Implicit conversions of integral types to bool are replaced with explicit comparisons to 0.

Examples:

1.  The ternary assignment bool b = (i < 0) ? true : false; has redundant parentheses and becomes bool b = i < 0;.

2.  The conditional return if (!b) return false; return true; has an implied double negation and becomes return b;.

3.  The conditional return if (i < 0) return false; return true; becomes return i >= 0;.

    The conditional return if (i != 0) return false; return true; becomes return i == 0;.

4.  The conditional return if (p) return true; return false; has an implicit conversion of a pointer to bool and becomes return p != nullptr;.

    The ternary assignment bool b = (i & 1) ? true : false; has an implicit conversion of i & 1 to bool and becomes bool b = (i & 1) != 0;.

5.  The conditional return if (i & 1) return true; else return false; has an implicit conversion of an integer quantity i & 1 to bool and becomes return (i & 1) != 0;

6.  Given struct X { explicit operator bool(); };, and an instance x of struct X, the conditional return if (x) return true; return false; becomes return static_cast<bool>(x);

  Options

ChainedConditionalReturn
    If non-zero, conditional boolean return statements at the end of an if/else if chain will be transformed. Default is 0.

ChainedConditionalAssignment
    If non-zero, conditional boolean assignments at the end of an if/else if chain will be transformed. Default is 0.

  readability-static-definition-in-anonymous-namespace

Finds static function and variable definitions in anonymous namespace.

In this case, static is redundant, because anonymous namespace limits the visibility of definitions to a single translation unit.

namespace {
  static int a = 1; // Warning.
  static const b = 1; // Warning.
}

The check will apply a fix by removing the redundant static qualifier.

  readability-uniqueptr-delete-release

Replace delete <unique_ptr>.release() with <unique_ptr> = nullptr. The latter is shorter, simpler and does not require use of raw pointer APIs.

clang-tidy is a clang-based C++ “linter” tool. Its purpose is to provide an extensible framework for diagnosing and fixing typical programming errors, like style violations, interface misuse, or bugs that can be deduced via static analysis. clang-tidy is modular and provides a convenient interface for writing new checks.

  Using clang-tidy

clang-tidy is a LibTooling-based tool, and it’s easier to work with if you set up a compile command database for your project (for an example of how to do this see How To Setup Tooling For LLVM). You can also specify compilation options on the command line after --:

$ clang-tidy test.cpp -- -Imy_project/include -DMY_DEFINES ...

clang-tidy has its own checks and can also run Clang static analyzer checks. Each check has a name and the checks to run can be chosen using the -checks= option, which specifies a comma-separated list of positive and negative (prefixed with -) globs. Positive globs add subsets of checks, negative globs remove them. For example,

$ clang-tidy test.cpp -checks=-*,clang-analyzer-*,-clang-analyzer-cplusplus*

will disable all default checks (-*) and enable all clang-analyzer-* checks except for clang-analyzer-cplusplus* ones.

The -list-checks option lists all the enabled checks. When used without -checks=, it shows checks enabled by default. Use -checks=* to see all available checks or with any other value of -checks= to see which checks are enabled by this value.

There are currently the following groups of checks:
Name prefix | Description
boost- | Checks related to Boost library.
cert- | Checks related to CERT Secure Coding Guidelines.
cppcoreguidelines- | Checks related to C++ Core Guidelines.
clang-analyzer- | Clang Static Analyzer checks.
google- | Checks related to the Google coding conventions.
llvm- | Checks related to the LLVM coding conventions.
misc- | Checks that we didn’t have a better category for.
modernize- | Checks that advocate usage of modern (currently “modern” means “C++11”) language constructs.
mpi- | Checks related to MPI (Message Passing Interface).
performance- | Checks that target performance-related issues.
readability- | Checks that target readability-related issues that don’t relate to any particular coding style.

Clang diagnostics are treated in a similar way as check diagnostics. Clang diagnostics are displayed by clang-tidy and can be filtered out using -checks= option. However, the -checks= option does not affect compilation arguments, so it can not turn on Clang warnings which are not already turned on in build configuration. The -warnings-as-errors= option upgrades any warnings emitted under the -checks= flag to errors (but it does not enable any checks itself).

Clang diagnostics have check names starting with clang-diagnostic-. Diagnostics which have a corresponding warning option, are named clang-diagnostic-<warning-option>, e.g. Clang warning controlled by -Wliteral-conversion will be reported with check name clang-diagnostic-literal-conversion.

The -fix flag instructs clang-tidy to fix found errors if supported by corresponding checks.

An overview of all the command-line options:

$ clang-tidy -help
USAGE: clang-tidy [options] <source0> [... <sourceN>]
OPTIONS:
Generic Options:
  -help                        - Display available options (-help-hidden for more)
  -help-list                   - Display list of available options (-help-list-hidden for more)
  -version                     - Display the version of this program
clang-tidy options:
  -analyze-temporary-dtors     -
                                 Enable temporary destructor-aware analysis in
                                 clang-analyzer- checks.
                                 This option overrides the value read from a
                                 .clang-tidy file.
  -checks=<string>             -
                                 Comma-separated list of globs with optional '-'
                                 prefix. Globs are processed in order of
                                 appearance in the list. Globs without '-'
                                 prefix add checks with matching names to the
                                 set, globs with the '-' prefix remove checks
                                 with matching names from the set of enabled
                                 checks. This option's value is appended to the
                                 value of the 'Checks' option in .clang-tidy
                                 file, if any.
  -config=<string>             -
                                 Specifies a configuration in YAML/JSON format:
                                   -config="{Checks: '*',
                                             CheckOptions: [{key: x,
                                                             value: y}]}"
                                 When the value is empty, clang-tidy will
                                 attempt to find a file named .clang-tidy for
                                 each source file in its parent directories.
  -dump-config                 -
                                 Dumps configuration in the YAML format to
                                 stdout. This option can be used along with a
                                 file name (and '--' if the file is outside of a
                                 project with configured compilation database).
                                 The configuration used for this file will be
                                 printed.
                                 Use along with -checks=* to include
                                 configuration of all checks.
  -enable-check-profile        -
                                 Enable per-check timing profiles, and print a
                                 report to stderr.
  -explain-config              -
                                 For each enabled check explains, where it is
                                 enabled, i.e. in clang-tidy binary, command
                                 line or a specific configuration file.
  -export-fixes=<filename>     -
                                 YAML file to store suggested fixes in. The
                                 stored fixes can be applied to the input source
                                 code with clang-apply-replacements.
  -extra-arg=<string>          - Additional argument to append to the compiler command line
  -extra-arg-before=<string>   - Additional argument to prepend to the compiler command line
  -fix                         -
                                 Apply suggested fixes. Without -fix-errors
                                 clang-tidy will bail out if any compilation
                                 errors were found.
  -fix-errors                  -
                                 Apply suggested fixes even if compilation
                                 errors were found. If compiler errors have
                                 attached fix-its, clang-tidy will apply them as
                                 well.
  -header-filter=<string>      -
                                 Regular expression matching the names of the
                                 headers to output diagnostics from. Diagnostics
                                 from the main file of each translation unit are
                                 always displayed.
                                 Can be used together with -line-filter.
                                 This option overrides the 'HeaderFilter' option
                                 in .clang-tidy file, if any.
  -line-filter=<string>        -
                                 List of files with line ranges to filter the
                                 warnings. Can be used together with
                                 -header-filter. The format of the list is a
                                 JSON array of objects:
                                   [
                                     {"name":"file1.cpp","lines":[[1,3],[5,7]]},
                                     {"name":"file2.h"}
                                   ]
  -list-checks                 -
                                 List all enabled checks and exit. Use with
                                 -checks=* to list all available checks.
  -p=<string>                  - Build path
  -style=<string>              -
                                 Fallback style for reformatting after inserting fixes
                                 if there is no clang-format config file found.
  -system-headers              - Display the errors from system headers.
  -warnings-as-errors=<string> -
                                 Upgrades warnings to errors. Same format as
                                 '-checks'.
                                 This option's value is appended to the value of
                                 the 'WarningsAsErrors' option in .clang-tidy
                                 file, if any.
-p <build-path> is used to read a compile command database.
        For example, it can be a CMake build directory in which a file named
        compile_commands.json exists (use -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
        CMake option to get this output). When no build path is specified,
        a search for compile_commands.json will be attempted through all
        parent paths of the first input file . See:
        http://clang.llvm.org/docs/HowToSetupToolingForLLVM.html for an
        example of setting up Clang Tooling on a source tree.
<source0> ... specify the paths of source files. These paths are
        looked up in the compile command database. If the path of a file is
        absolute, it needs to point into CMake's source tree. If the path is
        relative, the current working directory needs to be in the CMake
        source tree and the file must be in a subdirectory of the current
        working directory. "./" prefixes in the relative files will be
        automatically removed, but the rest of a relative path must be a
        suffix of a path in the compile command database.
Configuration files:
  clang-tidy attempts to read configuration for each source file from a
  .clang-tidy file located in the closest parent directory of the source
  file. If any configuration options have a corresponding command-line
  option, command-line option takes precedence. The effective
  configuration can be inspected using -dump-config:
    $ clang-tidy -dump-config - --
    ---
    Checks:          '-*,some-check'
    WarningsAsErrors: ''
    HeaderFilterRegex: ''
    AnalyzeTemporaryDtors: false
    User:            user
    CheckOptions:
      - key:             some-check.SomeOption
        value:           'some value'
    ...

  Getting Involved

clang-tidy has several own checks and can run Clang static analyzer checks, but its power is in the ability to easily write custom checks.

Checks are organized in modules, which can be linked into clang-tidy with minimal or no code changes in clang-tidy.

Checks can plug into the analysis on the preprocessor level using PPCallbacks or on the AST level using AST Matchers. When an error is found, checks can report them in a way similar to how Clang diagnostics work. A fix-it hint can be attached to a diagnostic message.

The interface provided by clang-tidy makes it easy to write useful and precise checks in just a few lines of code. If you have an idea for a good check, the rest of this document explains how to do this.

There are a few tools particularly useful when developing clang-tidy checks:

•   add_new_check.py is a script to automate the process of adding a new check, it will create the check, update the CMake file and create a test;

•   rename_check.py does what the script name suggests, renames an existing check;

•   clang-query is invaluable for interactive prototyping of AST matchers and exploration of the Clang AST;

•   clang-check with the -ast-dump (and optionally -ast-dump-filter) provides a convenient way to dump AST of a C++ program.

  Choosing the Right Place for your Check

If you have an idea of a check, you should decide whether it should be implemented as a:

•   Clang diagnostic: if the check is generic enough, targets code patterns that most probably are bugs (rather than style or readability issues), can be implemented effectively and with extremely low false positive rate, it may make a good Clang diagnostic.

•   Clang static analyzer check: if the check requires some sort of control flow analysis, it should probably be implemented as a static analyzer check.

•   clang-tidy check is a good choice for linter-style checks, checks that are related to a certain coding style, checks that address code readability, etc.

  Preparing your Workspace

If you are new to LLVM development, you should read the Getting Started with the LLVM System, Using Clang Tools and How To Setup Tooling For LLVM documents to check out and build LLVM, Clang and Clang Extra Tools with CMake.

Once you are done, change to the llvm/tools/clang/tools/extra directory, and let’s start!

  The Directory Structure

clang-tidy source code resides in the llvm/tools/clang/tools/extra directory and is structured as follows:

clang-tidy/                       # Clang-tidy core.
|-- ClangTidy.h                   # Interfaces for users and checks.
|-- ClangTidyModule.h             # Interface for clang-tidy modules.
|-- ClangTidyModuleRegistry.h     # Interface for registering of modules.
   ...
|-- google/                       # Google clang-tidy module.
|-+
  |-- GoogleTidyModule.cpp
  |-- GoogleTidyModule.h
        ...
|-- llvm/                         # LLVM clang-tidy module.
|-+
  |-- LLVMTidyModule.cpp
  |-- LLVMTidyModule.h
        ...
|-- tool/                         # Sources of the clang-tidy binary.
        ...
test/clang-tidy/                  # Integration tests.
    ...
unittests/clang-tidy/             # Unit tests.
|-- ClangTidyTest.h
|-- GoogleModuleTest.cpp
|-- LLVMModuleTest.cpp
    ...

  Writing a clang-tidy Check

So you have an idea of a useful check for clang-tidy.

First, if you’re not familiar with LLVM development, read through the Getting Started with LLVM document for instructions on setting up your workflow and the LLVM Coding Standards document to familiarize yourself with the coding style used in the project. For code reviews we mostly use LLVM Phabricator.

Next, you need to decide which module the check belongs to. Modules are located in subdirectories of clang-tidy/ and contain checks targeting a certain aspect of code quality (performance, readability, etc.), certain coding style or standard (Google, LLVM, CERT, etc.) or a widely used API (e.g. MPI). Their names are same as user-facing check groups names described above.

After choosing the module and the name for the check, run the clang-tidy/add_new_check.py script to create the skeleton of the check and plug it to clang-tidy. It’s the recommended way of adding new checks.

If we want to create a readability-awesome-function-names, we would run:

$ clang-tidy/add_new_check.py readability awesome-function-names

The add_new_check.py script will:

•   create the class for your check inside the specified module’s directory and register it in the module and in the build system;

•   create a lit test file in the test/clang-tidy/ directory;

•   create a documentation file and include it into the docs/clang-tidy/checks/list.rst.

    Let’s see in more detail at the check class definition:

    ...
    #include "../ClangTidy.h"
    namespace clang {
    namespace tidy {
    namespace readability {
    ...
    class AwesomeFunctionNamesCheck : public ClangTidyCheck {
    public:
      AwesomeFunctionNamesCheck(StringRef Name, ClangTidyContext *Context)
          : ClangTidyCheck(Name, Context) {}
      void registerMatchers(ast_matchers::MatchFinder *Finder) override;
      void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
    };
    } // namespace readability
    } // namespace tidy
    } // namespace clang
    ...

    Constructor of the check receives the Name and Context parameters, and must forward them to the ClangTidyCheck constructor.

    In our case the check needs to operate on the AST level and it overrides the registerMatchers and check methods. If we wanted to analyze code on the preprocessor level, we’d need instead to override the registerPPCallbacks method.

    In the registerMatchers method we create an AST Matcher (see AST Matchers for more information) that will find the pattern in the AST that we want to inspect. The results of the matching are passed to the check method, which can further inspect them and report diagnostics.

    using namespace ast_matchers;
    void AwesomeFunctionNamesCheck::registerMatchers(MatchFinder *Finder) {
      Finder->addMatcher(functionDecl().bind("x"), this);
    }
    void AwesomeFunctionNamesCheck::check(const MatchFinder::MatchResult &Result) {
      const auto *MatchedDecl = Result.Nodes.getNodeAs<FunctionDecl>("x");
      if (MatchedDecl->getName().startswith("awesome_"))
        return;
      diag(MatchedDecl->getLocation(), "function %0 is insufficiently awesome")
          << MatchedDecl
          << FixItHint::CreateInsertion(MatchedDecl->getLocation(), "awesome_");
    }

    (If you want to see an example of a useful check, look at clang-tidy/google/ExplicitConstructorCheck.h and clang-tidy/google/ExplicitConstructorCheck.cpp).

  Registering your Check

(The add_new_check.py takes care of registering the check in an existing module. If you want to create a new module or know the details, read on.)

The check should be registered in the corresponding module with a distinct name:

class MyModule : public ClangTidyModule {
 public:
  void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
    CheckFactories.registerCheck<ExplicitConstructorCheck>(
        "my-explicit-constructor");
  }
};

Now we need to register the module in the ClangTidyModuleRegistry using a statically initialized variable:

static ClangTidyModuleRegistry::Add<MyModule> X("my-module",
                                                "Adds my lint checks.");

When using LLVM build system, we need to use the following hack to ensure the module is linked into the clang-tidy binary:

Add this near the ClangTidyModuleRegistry::Add<MyModule> variable:

// This anchor is used to force the linker to link in the generated object file
// and thus register the MyModule.
volatile int MyModuleAnchorSource = 0;

And this to the main translation unit of the clang-tidy binary (or the binary you link the clang-tidy library in) clang-tidy/tool/ClangTidyMain.cpp:

// This anchor is used to force the linker to link the MyModule.
extern volatile int MyModuleAnchorSource;
static int MyModuleAnchorDestination = MyModuleAnchorSource;

  Configuring Checks

If a check needs configuration options, it can access check-specific options using the Options.get<Type>("SomeOption", DefaultValue) call in the check constructor. In this case the check should also override the ClangTidyCheck::storeOptions method to make the options provided by the check discoverable. This method lets clang-tidy know which options the check implements and what the current values are (e.g. for the -dump-config command line option).

class MyCheck : public ClangTidyCheck {
  const unsigned SomeOption1;
  const std::string SomeOption2;
public:
  MyCheck(StringRef Name, ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      SomeOption(Options.get("SomeOption1", -1U)),
      SomeOption(Options.get("SomeOption2", "some default")) {}
  void storeOptions(ClangTidyOptions::OptionMap &Opts) override {
    Options.store(Opts, "SomeOption1", SomeOption1);
    Options.store(Opts, "SomeOption2", SomeOption2);
  }
  ...

Assuming the check is registered with the name “my-check”, the option can then be set in a .clang-tidy file in the following way:

CheckOptions:
  - key: my-check.SomeOption1
    value: 123
  - key: my-check.SomeOption2
    value: 'some other value'

If you need to specify check options on a command line, you can use the inline YAML format:

$ clang-tidy -config="{CheckOptions: [{key: a, value: b}, {key: x, value: y}]}" ...

  Testing Checks

clang-tidy checks can be tested using either unit tests or lit tests. Unit tests may be more convenient to test complex replacements with strict checks. Lit tests allow using partial text matching and regular expressions which makes them more suitable for writing compact tests for diagnostic messages.

The check_clang_tidy.py script provides an easy way to test both diagnostic messages and fix-its. It filters out CHECK lines from the test file, runs clang-tidy and verifies messages and fixes with two separate FileCheck invocations: once with FileCheck’s directive prefix set to CHECK-MESSAGES, validating the diagnostic messages, and once with the directive prefix set to CHECK-FIXES, running against the fixed code (i.e., the code after generated fixits are applied). In particular, CHECK-FIXES: can be used to check that code was not modified by fixits, by checking that it is present unchanged in the fixed code. The full set of FileCheck directives is available (e.g., CHECK-MESSAGES-SAME:, CHECK-MESSAGES-NOT:), though typically the basic CHECK forms (CHECK-MESSAGES and CHECK-FIXES) are sufficient for clang-tidy tests. Note that the FileCheck documentation mostly assumes the default prefix (CHECK), and hence describes the directive as CHECK:, CHECK-SAME:, CHECK-NOT:, etc. Replace CHECK by either CHECK-FIXES or CHECK-MESSAGES for clang-tidy tests.

An additional check enabled by check_clang_tidy.py ensures that if CHECK-MESSAGES: is used in a file then every warning or error must have an associated CHECK in that file.

To use the check_clang_tidy.py script, put a .cpp file with the appropriate RUN line in the test/clang-tidy directory. Use CHECK-MESSAGES: and CHECK-FIXES: lines to write checks against diagnostic messages and fixed code.

It’s advised to make the checks as specific as possible to avoid checks matching to incorrect parts of the input. Use [[@LINE+X]]/[[@LINE-X]] substitutions and distinct function and variable names in the test code.

Here’s an example of a test using the check_clang_tidy.py script (the full source code is at test/clang-tidy/google-readability-casting.cpp):

// RUN: %check_clang_tidy %s google-readability-casting %t
void f(int a) {
  int b = (int)a;
  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: redundant cast to the same type [google-readability-casting]
  // CHECK-FIXES: int b = a;
}

There are many dark corners in the C++ language, and it may be difficult to make your check work perfectly in all cases, especially if it issues fix-it hints. The most frequent pitfalls are macros and templates:

1.  code written in a macro body/template definition may have a different meaning depending on the macro expansion/template instantiation;

2.  multiple macro expansions/template instantiations may result in the same code being inspected by the check multiple times (possibly, with different meanings, see 1), and the same warning (or a slightly different one) may be issued by the check multiple times; clang-tidy will deduplicate _identical_ warnings, but if the warnings are slightly different, all of them will be shown to the user (and used for applying fixes, if any);

3.  making replacements to a macro body/template definition may be fine for some macro expansions/template instantiations, but easily break some other expansions/instantiations.

  Running clang-tidy on LLVM

To test a check it’s best to try it out on a larger code base. LLVM and Clang are the natural targets as you already have the source code around. The most convenient way to run clang-tidy is with a compile command database; CMake can automatically generate one, for a description of how to enable it see How To Setup Tooling For LLVM. Once compile_commands.json is in place and a working version of clang-tidy is in PATH the entire code base can be analyzed with clang-tidy/tool/run-clang-tidy.py. The script executes clang-tidy with the default set of checks on every translation unit in the compile command database and displays the resulting warnings and errors. The script provides multiple configuration flags.

•   The default set of checks can be overridden using the -checks argument, taking the identical format as clang-tidy does. For example -checks=-*,modernize-use-override will run the modernize-use-override check only.

•   To restrict the files examined you can provide one or more regex arguments that the file names are matched against. run-clang-tidy.py clang-tidy/.*Check\.cpp will only analyze clang-tidy checkers. It may also be necessary to restrict the header files warnings are displayed from using the -header-filter flag. It has the same behavior as the corresponding clang-tidy flag.

•   To apply suggested fixes -fix can be passed as an argument. This gathers all changes in a temporary directory and applies them. Passing -format will run clang-format over changed lines.

CLANG-INCLUDE-FIXER

  Contents

•   Clang-Include-Fixer

•   Setup

•   Creating a Symbol Index From a Compilation Database

•   Integrate with Vim

•   Integrate with Emacs

•   How it Works

    One of the major nuisances of C++ compared to other languages is the manual management of #include directives in any file. clang-include-fixer addresses one aspect of this problem by providing an automated way of adding #include directives for missing symbols in one translation unit.

    While inserting missing #include, clang-include-fixer adds missing namespace qualifiers to all instances of an unidentified symbol if the symbol is missing some prefix namespace qualifiers.

  Setup

To use clang-include-fixer two databases are required. Both can be generated with existing tools.

•   Compilation database. Contains the compiler commands for any given file in a project and can be generated by CMake, see How To Setup Tooling For LLVM.

•   Symbol index. Contains all symbol information in a project to match a given identifier to a header file.

    Ideally both databases (compile_commands.json and find_all_symbols_db.yaml) are linked into the root of the source tree they correspond to. Then the clang-include-fixer can automatically pick them up if called with a source file from that tree. Note that by default compile_commands.json as generated by CMake does not include header files, so only implementation files can be handled by tools.

  Creating a Symbol Index From a Compilation Database

The include fixer contains find-all-symbols, a tool to create a symbol database in YAML format from a compilation database by parsing all source files listed in it. The following list of commands shows how to set up a database for LLVM, any project built by CMake should follow similar steps.

$ cd path/to/llvm-build
$ ninja find-all-symbols // build find-all-symbols tool.
$ ninja clang-include-fixer // build clang-include-fixer tool.
$ ls compile_commands.json # Make sure compile_commands.json exists.
  compile_commands.json
$ path/to/llvm/source/tools/clang/tools/extra/include-fixer/find-all-symbols/tool/run-find-all-symbols.py
  ... wait as clang indexes the code base ...
$ ln -s $PWD/find_all_symbols_db.yaml path/to/llvm/source/ # Link database into the source tree.
$ ln -s $PWD/compile_commands.json path/to/llvm/source/ # Also link compilation database if it's not there already.
$ cd path/to/llvm/source
$ /path/to/clang-include-fixer -db=yaml path/to/file/with/missing/include.cpp
  Added #include "foo.h"

  Integrate with Vim

To run clang-include-fixer on a potentially unsaved buffer in Vim. Add the following key binding to your .vimrc:

noremap <leader>cf :pyf path/to/llvm/source/tools/clang/tools/extra/include-fixer/tool/clang-include-fixer.py<cr>

This enables clang-include-fixer for NORMAL and VISUAL mode. Change <leader>cf to another binding if you need clang-include-fixer on a different key. The <leader> key is a reference to a specific key defined by the mapleader variable and is bound to backslash by default.

Make sure vim can find clang-include-fixer:

•   Add the path to clang-include-fixer to the PATH environment variable.

•   Or set g:clang_include_fixer_path in vimrc: let g:clang_include_fixer_path=path/to/clang-include-fixer

    You can customize the number of headers being shown by setting let g:clang_include_fixer_maximum_suggested_headers=5

    Customized settings in .vimrc:

•   let g:clang_include_fixer_path = "clang-include-fixer"

    Set clang-include-fixer binary file path.

•   let g:clang_include_fixer_maximum_suggested_headers = 3

    Set the maximum number of #includes to show. Default is 3.

•   let g:clang_include_fixer_increment_num = 5

    Set the increment number of #includes to show every time when pressing m. Default is 5.

•   let g:clang_include_fixer_jump_to_include = 0

    Set to 1 if you want to jump to the new inserted #include line. Default is 0.

•   let g:clang_include_fixer_query_mode = 0

    Set to 1 if you want to insert #include for the symbol under the cursor. Default is 0. Compared to normal mode, this mode won’t parse the source file and only search the sysmbol from database, which is faster than normal mode.

    See clang-include-fixer.py for more details.

  Integrate with Emacs

To run clang-include-fixer on a potentially unsaved buffer in Emacs. Ensure that Emacs finds clang-include-fixer.el by adding the directory containing the file to the load-path and requiring the clang-include-fixer in your .emacs:

(add-to-list 'load-path "path/to/llvm/source/tools/clang/tools/extra/include-fixer/tool/"
(require 'clang-include-fixer)

Within Emacs the tool can be invoked with the command M-x clang-include-fixer. This will insert the header that defines the first undefined symbol; if there is more than one header that would define the symbol, the user is prompted to select one.

To include the header that defines the symbol at point, run M-x clang-include-fixer-at-point.

Make sure Emacs can find clang-include-fixer:

•   Either add the parent directory of clang-include-fixer to the PATH environment variable, or customize the Emacs user option clang-include-fixer-executable to point to the file name of the program.

  How it Works

To get the most information out of Clang at parse time, clang-include-fixer runs in tandem with the parse and receives callbacks from Clang’s semantic analysis. In particular it reuses the existing support for typo corrections. Whenever Clang tries to correct a potential typo it emits a callback to the include fixer which then looks for a corresponding file. At this point rich lookup information is still available, which is not available in the AST at a later stage.

The identifier that should be typo corrected is then sent to the database, if a header file is returned it is added as an include directive at the top of the file.

Currently clang-include-fixer only inserts a single include at a time to avoid getting caught in follow-up errors. If multiple #include additions are desired the program can be rerun until a fix-point is reached.

MODULARIZE USER’S MANUAL

  Modularize Usage

modularize [<modularize-options>] [<module-map>|<include-files-list>]* [<front-end-options>...]

<modularize-options> is a place-holder for options specific to modularize, which are described below in Modularize Command Line Options.

<module-map> specifies the path of a file name for an existing module map. The module map must be well-formed in terms of syntax. Modularize will extract the header file names from the map. Only normal headers are checked, assuming headers marked “private”, “textual”, or “exclude” are not to be checked as a top-level include, assuming they either are included by other headers which are checked, or they are not suitable for modules.

<include-files-list> specifies the path of a file name for a file containing the newline-separated list of headers to check with respect to each other. Lines beginning with ‘#’ and empty lines are ignored. Header file names followed by a colon and other space-separated file names will include those extra files as dependencies. The file names can be relative or full paths, but must be on the same line. For example:

header1.h
header2.h
header3.h: header1.h header2.h

Note that unless a -prefix (header path) option is specified, non-absolute file paths in the header list file will be relative to the header list file directory. Use -prefix to specify a different directory.

<front-end-options> is a place-holder for regular Clang front-end arguments, which must follow the <include-files-list>. Note that by default, modularize assumes .h files contain C++ source, so if you are using a different language, you might need to use a -x option to tell Clang that the header contains another language, i.e.: -x c

Note also that because modularize does not use the clang driver, you will likely need to pass in additional compiler front-end arguments to match those passed in by default by the driver.

  Modularize Command Line Options

-prefix=<header-path>
    Prepend the given path to non-absolute file paths in the header list file. By default, headers are assumed to be relative to the header list file directory. Use -prefix to specify a different directory.

-module-map-path=<module-map-path>
    Generate a module map and output it to the given file. See the description in module-map-generation.

-problem-files-list=<problem-files-list-file-name>
    For use only with module map assistant. Input list of files that have problems with respect to modules. These will still be included in the generated module map, but will be marked as “excluded” headers.

-root-module=<root-name>
    Put modules generated by the -module-map-path option in an enclosing module with the given name. See the description in module-map-generation.

-block-check-header-list-only
    Limit the #include-inside-extern-or-namespace-block check to only those headers explicitly listed in the header list. This is a work-around for avoiding error messages for private includes that purposefully get included inside blocks.

-no-coverage-check
    Don’t do the coverage check for a module map.

-coverage-check-only
    Only do the coverage check for a module map.

-display-file-lists
    Display lists of good files (no compile errors), problem files, and a combined list with problem files preceded by a ‘#’. This can be used to quickly determine which files have problems. The latter combined list might be useful in starting to modularize a set of headers. You can start with a full list of headers, use -display-file-lists option, and then use the combined list as your intermediate list, uncommenting-out headers as you fix them.

    modularize is a standalone tool that checks whether a set of headers provides the consistent definitions required to use modules. For example, it detects whether the same entity (say, a NULL macro or size_t typedef) is defined in multiple headers or whether a header produces different definitions under different circumstances. These conditions cause modules built from the headers to behave poorly, and should be fixed before introducing a module map.

    modularize also has an assistant mode option for generating a module map file based on the provided header list. The generated file is a functional module map that can be used as a starting point for a module.map file.

  Getting Started

To build from source:

1.  Read Getting Started with the LLVM System and Clang Tools Documentation for information on getting sources for LLVM, Clang, and Clang Extra Tools.

2.  Getting Started with the LLVM System and Building LLVM with CMake give directions for how to build. With sources all checked out into the right place the LLVM build will build Clang Extra Tools and their dependencies automatically.

•   If using CMake, you can also use the modularize target to build just the modularize tool and its dependencies.

    Before continuing, take a look at ModularizeUsage to see how to invoke modularize.

  What Modularize Checks

Modularize will check for the following:

•   Duplicate global type and variable definitions

•   Duplicate macro definitions

•   Macro instances, ‘defined(macro)’, or #if, #elif, #ifdef, #ifndef conditions that evaluate differently in a header

•   #include directives inside ‘extern “C/C++” {}’ or ‘namespace (name) {}’ blocks

•   Module map header coverage completeness (in the case of a module map input only)

    Modularize will do normal C/C++ parsing, reporting normal errors and warnings, but will also report special error messages like the following:

    error: '(symbol)' defined at multiple locations:
       (file):(row):(column)
       (file):(row):(column)
    error: header '(file)' has different contents depending on how it was included

    The latter might be followed by messages like the following:

    note: '(symbol)' in (file) at (row):(column) not always provided

    Checks will also be performed for macro expansions, defined(macro) expressions, and preprocessor conditional directives that evaluate inconsistently, and can produce error messages like the following:

     (...)/SubHeader.h:11:5:
    #if SYMBOL == 1
        ^
    error: Macro instance 'SYMBOL' has different values in this header,
           depending on how it was included.
      'SYMBOL' expanded to: '1' with respect to these inclusion paths:
        (...)/Header1.h
          (...)/SubHeader.h
    (...)/SubHeader.h:3:9:
    #define SYMBOL 1
            ^
    Macro defined here.
      'SYMBOL' expanded to: '2' with respect to these inclusion paths:
        (...)/Header2.h
            (...)/SubHeader.h
    (...)/SubHeader.h:7:9:
    #define SYMBOL 2
            ^
    Macro defined here.

    Checks will also be performed for ‘#include’ directives that are nested inside ‘extern “C/C++” {}’ or ‘namespace (name) {}’ blocks, and can produce error message like the following:

    IncludeInExtern.h:2:3:
    #include "Empty.h"
    ^
    error: Include directive within extern "C" {}.
    IncludeInExtern.h:1:1:
    extern "C" {
    ^
    The "extern "C" {}" block is here.

  Module Map Coverage Check

The coverage check uses the Clang library to read and parse the module map file. Starting at the module map file directory, or just the include paths, if specified, it will collect the names of all the files it considers headers (no extension, .h, or .inc–if you need more, modify the isHeader function). It then compares the headers against those referenced in the module map, either explicitly named, or implicitly named via an umbrella directory or umbrella file, as parsed by the ModuleMap object. If headers are found which are not referenced or covered by an umbrella directory or file, warning messages will be produced, and this program will return an error code of 1. If no problems are found, an error code of 0 is returned.

Note that in the case of umbrella headers, this tool invokes the compiler to preprocess the file, and uses a callback to collect the header files included by the umbrella header or any of its nested includes. If any front end options are needed for these compiler invocations, these can be included on the command line after the module map file argument.

Warning message have the form: warning: module.modulemap does not account for file: Level3A.h

Note that for the case of the module map referencing a file that does not exist, the module map parser in Clang will (at the time of this writing) display an error message.

To limit the checks modularize does to just the module map coverage check, use the -coverage-check-only option.

For example:

modularize -coverage-check-only module.modulemap

  Module Map Generation

If you specify the -module-map-path=<module map file>, modularize will output a module map based on the input header list. A module will be created for each header. Also, if the header in the header list is a partial path, a nested module hierarchy will be created in which a module will be created for each subdirectory component in the header path, with the header itself represented by the innermost module. If other headers use the same subdirectories, they will be enclosed in these same modules also.

For example, for the header list:

SomeTypes.h
SomeDecls.h
SubModule1/Header1.h
SubModule1/Header2.h
SubModule2/Header3.h
SubModule2/Header4.h
SubModule2.h

The following module map will be generated:

// Output/NoProblemsAssistant.txt
// Generated by: modularize -module-map-path=Output/NoProblemsAssistant.txt \
     -root-module=Root NoProblemsAssistant.modularize
module SomeTypes {
  header "SomeTypes.h"
  export *
}
module SomeDecls {
  header "SomeDecls.h"
  export *
}
module SubModule1 {
  module Header1 {
    header "SubModule1/Header1.h"
    export *
  }
  module Header2 {
    header "SubModule1/Header2.h"
    export *
  }
}
module SubModule2 {
  module Header3 {
    header "SubModule2/Header3.h"
    export *
  }
  module Header4 {
    header "SubModule2/Header4.h"
    export *
  }
  header "SubModule2.h"
  export *
}

An optional -root-module=<root-name> option can be used to cause a root module to be created which encloses all the modules.

An optional -problem-files-list=<problem-file-name> can be used to input a list of files to be excluded, perhaps as a temporary stop-gap measure until problem headers can be fixed.

For example, with the same header list from above:

// Output/NoProblemsAssistant.txt
// Generated by: modularize -module-map-path=Output/NoProblemsAssistant.txt \
     -root-module=Root NoProblemsAssistant.modularize
module Root {
  module SomeTypes {
    header "SomeTypes.h"
    export *
  }
  module SomeDecls {
    header "SomeDecls.h"
    export *
  }
  module SubModule1 {
    module Header1 {
      header "SubModule1/Header1.h"
      export *
    }
    module Header2 {
      header "SubModule1/Header2.h"
      export *
    }
  }
  module SubModule2 {
    module Header3 {
      header "SubModule2/Header3.h"
      export *
    }
    module Header4 {
      header "SubModule2/Header4.h"
      export *
    }
    header "SubModule2.h"
    export *
  }
}

Note that headers with dependents will be ignored with a warning, as the Clang module mechanism doesn’t support headers the rely on other headers to be included first.

The module map format defines some keywords which can’t be used in module names. If a header has one of these names, an underscore (‘_’) will be prepended to the name. For example, if the header name is header.h, because header is a keyword, the module name will be _header. For a list of the module map keywords, please see: Lexical structure

PP-TRACE USER’S MANUAL

pp-trace is a standalone tool that traces preprocessor activity. It’s also used as a test of Clang’s PPCallbacks interface. It runs a given source file through the Clang preprocessor, displaying selected information from callback functions overridden in a PPCallbacks derivation. The output is in a high-level YAML format, described in pp-trace Output Format.

  pp-trace Usage

  Command Line Format

pp-trace [<pp-trace-options>] <source-file> [<front-end-options>]

<pp-trace-options> is a place-holder for options specific to pp-trace, which are described below in Command Line Options.

<source-file> specifies the source file to run through the preprocessor.

<front-end-options> is a place-holder for regular Clang Compiler Options, which must follow the <source-file>.

  Command Line Options

-ignore <callback-name-list>
    This option specifies a comma-separated list of names of callbacks that shouldn’t be traced. It can be used to eliminate unwanted trace output. The callback names are the name of the actual callback function names in the PPCallbacks class:

•   FileChanged

•   FileSkipped

•   FileNotFound

•   InclusionDirective

•   moduleImport

•   EndOfMainFile

•   Ident

•   PragmaDirective

•   PragmaComment

•   PragmaDetectMismatch

•   PragmaDebug

•   PragmaMessage

•   PragmaDiagnosticPush

•   PragmaDiagnosticPop

•   PragmaDiagnostic

•   PragmaOpenCLExtension

•   PragmaWarning

•   PragmaWarningPush

•   PragmaWarningPop

•   MacroExpands

•   MacroDefined

•   MacroUndefined

•   Defined

•   SourceRangeSkipped

•   If

•   Elif

•   Ifdef

•   Ifndef

•   Else

•   Endif

-output <output-file>
    By default, pp-trace outputs the trace information to stdout. Use this option to output the trace information to a file.

  pp-trace Output Format

The pp-trace output is formatted as YAML. See http://yaml.org/ for general YAML information. It’s arranged as a sequence of information about the callback call, including the callback name and argument information, for example::

---
- Callback: Name
  Argument1: Value1
  Argument2: Value2
(etc.)
...

With real data::

---
- Callback: FileChanged
  Loc: "c:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-include.cpp:1:1"
  Reason: EnterFile
  FileType: C_User
  PrevFID: (invalid)
  (etc.)
- Callback: FileChanged
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-include.cpp:5:1"
  Reason: ExitFile
  FileType: C_User
  PrevFID: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/Input/Level1B.h"
- Callback: EndOfMainFile
...

In all but one case (MacroDirective) the “Argument” scalars have the same name as the argument in the corresponding PPCallbacks callback function.

  Callback Details

The following sections describe the pupose and output format for each callback.

Click on the callback name in the section heading to see the Doxygen documentation for the callback.

The argument descriptions table describes the callback argument information displayed.

The Argument Name field in most (but not all) cases is the same name as the callback function parameter.

The Argument Value Syntax field describes the values that will be displayed for the argument value. It uses an ad hoc representation that mixes literal and symbolic representations. Enumeration member symbols are shown as the actual enum member in a (member1|member2|…) form. A name in parentheses can either represent a place holder for the described value, or confusingly, it might be a literal, such as (null), for a null pointer. Locations are shown as quoted only to avoid confusing the documentation generator.

The Clang C++ Type field is the type from the callback function declaration.

The description describes the argument or what is displayed for it.

Note that in some cases, such as when a structure pointer is an argument value, only some key member or members are shown to represent the value, instead of trying to display all members of the structure.

  FileChanged Callback

FileChanged is called when the preprocessor enters or exits a file, both the top level file being compiled, as well as any #include directives. It will also be called as a result of a system header pragma or in internal renaming of a file.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Reason | (EnterFile|ExitFile|SystemHeaderPragma|RenameFile) | PPCallbacks::FileChangeReason | Reason for change.
FileType | (C_User|C_System|C_ExternCSystem) | SrcMgr::CharacteristicKind | Include type.
PrevFID | ((file)|(invalid)) | FileID | Previous file, if any.

Example::

- Callback: FileChanged
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-include.cpp:1:1"
  Reason: EnterFile
  FileType: C_User
  PrevFID: (invalid)

  FileSkipped Callback

FileSkipped is called when a source file is skipped as the result of header guard optimization.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
ParentFile | (“(file)” or (null)) | const FileEntry | The file that #included the skipped file.
FilenameTok | (token) | const Token | The token in ParentFile that indicates the skipped file.
FileType | (C_User|C_System|C_ExternCSystem) | SrcMgr::CharacteristicKind | The file type.

Example::

- Callback: FileSkipped
  ParentFile: "/path/filename.h"
  FilenameTok: "filename.h"
  FileType: C_User

  FileNotFound Callback

FileNotFound is called when an inclusion directive results in a file-not-found error.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
FileName | “(file)” | StringRef | The name of the file being included, as written in the source code.
RecoveryPath | (path) | SmallVectorImpl<char> | If this client indicates that it can recover from this missing file, the client should set this as an additional header search patch.

Example::

- Callback: FileNotFound
  FileName: "/path/filename.h"
  RecoveryPath:

  InclusionDirective Callback

InclusionDirective is called when an inclusion directive of any kind (#include</code>, #import</code>, etc.) has been processed, regardless of whether the inclusion will actually result in an inclusion.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
HashLoc | “(file):(line):(col)” | SourceLocation | The location of the ‘#’ that starts the inclusion directive.
IncludeTok | (token) | const Token | The token that indicates the kind of inclusion directive, e.g., ‘include’ or ‘import’.
FileName | “(file)” | StringRef | The name of the file being included, as written in the source code.
IsAngled | (true|false) | bool | Whether the file name was enclosed in angle brackets; otherwise, it was enclosed in quotes.
FilenameRange | “(file)” | CharSourceRange | The character range of the quotes or angle brackets for the written file name.
File | “(file)” | const FileEntry | The actual file that may be included by this inclusion directive.
SearchPath | “(path)” | StringRef | Contains the search path which was used to find the file in the file system.
RelativePath | “(path)” | StringRef | The path relative to SearchPath, at which the include file was found.
Imported | ((module name)|(null)) | const Module | The module, whenever an inclusion directive was automatically turned into a module import or null otherwise.

Example::

- Callback: InclusionDirective
  IncludeTok: include
  FileName: "Input/Level1B.h"
  IsAngled: false
  FilenameRange: "Input/Level1B.h"
  File: "D:/Clang/llvmnewmod/tools/clang/tools/extra/test/pp-trace/Input/Level1B.h"
  SearchPath: "D:/Clang/llvmnewmod/tools/clang/tools/extra/test/pp-trace"
  RelativePath: "Input/Level1B.h"
  Imported: (null)

  moduleImport Callback

moduleImport is called when there was an explicit module-import syntax.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
ImportLoc | “(file):(line):(col)” | SourceLocation | The location of import directive token.
Path | “(path)” | ModuleIdPath | The identifiers (and their locations) of the module “path”.
Imported | ((module name)|(null)) | const Module | The imported module; can be null if importing failed.

Example::

- Callback: moduleImport
  ImportLoc: "d:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-modules.cpp:4:2"
  Path: [{Name: Level1B, Loc: "d:/Clang/llvmnewmod/tools/clang/tools/extra/test/pp-trace/pp-trace-modules.cpp:4:9"}, {Name: Level2B, Loc: "d:/Clang/llvmnewmod/tools/clang/tools/extra/test/pp-trace/pp-trace-modules.cpp:4:17"}]
  Imported: Level2B

  EndOfMainFile Callback

EndOfMainFile is called when the end of the main file is reached.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
(no arguments) |  |  |

Example::

- Callback: EndOfMainFile

  Ident Callback

Ident is called when a #ident or #sccs directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
str | (name) | const std::string | The text of the directive.

Example::

- Callback: Ident
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-ident.cpp:3:1"
  str: "$Id$"

  PragmaDirective Callback

PragmaDirective is called when start reading any pragma directive.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Introducer | (PIK_HashPragma|PIK__Pragma|PIK___pragma) | PragmaIntroducerKind | The type of the pragma directive.

Example::

- Callback: PragmaDirective
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  Introducer: PIK_HashPragma

  PragmaComment Callback

PragmaComment is called when a #pragma comment directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Kind | ((name)|(null)) | const IdentifierInfo | The comment kind symbol.
Str | (message directive) | const std::string | The comment message directive.

Example::

- Callback: PragmaComment
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  Kind: library
  Str: kernel32.lib

  PragmaDetectMismatch Callback

PragmaDetectMismatch is called when a #pragma detect_mismatch directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Name | “(name)” | const std::string | The name.
Value | (string) | const std::string | The value.

Example::

- Callback: PragmaDetectMismatch
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  Name: name
  Value: value

  PragmaDebug Callback

PragmaDebug is called when a #pragma clang __debug directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
DebugType | (string) | StringRef | Indicates type of debug message.

Example::

- Callback: PragmaDebug
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  DebugType: warning

  PragmaMessage Callback

PragmaMessage is called when a #pragma message directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Namespace | (name) | StringRef | The namespace of the message directive.
Kind | (PMK_Message|PMK_Warning|PMK_Error) | PPCallbacks::PragmaMessageKind | The type of the message directive.
Str | (string) | StringRef | The text of the message directive.

Example::

- Callback: PragmaMessage
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  Namespace: "GCC"
  Kind: PMK_Message
  Str: The message text.

  PragmaDiagnosticPush Callback

PragmaDiagnosticPush is called when a #pragma gcc dianostic push directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Namespace | (name) | StringRef | Namespace name.

Example::

- Callback: PragmaDiagnosticPush
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  Namespace: "GCC"

  PragmaDiagnosticPop Callback

PragmaDiagnosticPop is called when a #pragma gcc dianostic pop directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Namespace | (name) | StringRef | Namespace name.

Example::

- Callback: PragmaDiagnosticPop
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  Namespace: "GCC"

  PragmaDiagnostic Callback

PragmaDiagnostic is called when a #pragma gcc dianostic directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Namespace | (name) | StringRef | Namespace name.
mapping | (0|MAP_IGNORE|MAP_WARNING|MAP_ERROR|MAP_FATAL) | diag::Severity | Mapping type.
Str | (string) | StringRef | Warning/error name.

Example::

- Callback: PragmaDiagnostic
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  Namespace: "GCC"
  mapping: MAP_WARNING
  Str: WarningName

  PragmaOpenCLExtension Callback

PragmaOpenCLExtension is called when OpenCL extension is either disabled or enabled with a pragma.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
NameLoc | “(file):(line):(col)” | SourceLocation | The location of the name.
Name | (name) | const IdentifierInfo | Name symbol.
StateLoc | “(file):(line):(col)” | SourceLocation | The location of the state.
State | (1|0) | unsigned | Enabled/disabled state.

Example::

- Callback: PragmaOpenCLExtension
  NameLoc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:10"
  Name: Name
  StateLoc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:18"
  State: 1

  PragmaWarning Callback

PragmaWarning is called when a #pragma warning directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
WarningSpec | (string) | StringRef | The warning specifier.
Ids | [(number)[, …]] | ArrayRef<int> | The warning numbers.

Example::

- Callback: PragmaWarning
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  WarningSpec: disable
  Ids: 1,2,3

  PragmaWarningPush Callback

PragmaWarningPush is called when a #pragma warning(push) directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Level | (number) | int | Warning level.

Example::

- Callback: PragmaWarningPush
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
  Level: 1

  PragmaWarningPop Callback

PragmaWarningPop is called when a #pragma warning(pop) directive is read.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.

Example::

- Callback: PragmaWarningPop
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-pragma.cpp:3:1"

  MacroExpands Callback

MacroExpands is called when ::HandleMacroExpandedIdentifier when a macro invocation is found.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.
Range | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range for the expansion.
Args | [(name)|(number)|<(token name)>[, …]] | const MacroArgs | The argument tokens. Names and numbers are literal, everything else is of the form ‘<’ tokenName ‘>’.

Example::

- Callback: MacroExpands
  MacroNameTok: X_IMPL
  MacroDirective: MD_Define
  Range: [(nonfile), (nonfile)]
  Args: [a <plus> y, b]

  MacroDefined Callback

MacroDefined is called when a macro definition is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.

Example::

- Callback: MacroDefined
  MacroNameTok: X_IMPL
  MacroDirective: MD_Define

  MacroUndefined Callback

MacroUndefined is called when a macro #undef is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.

Example::

- Callback: MacroUndefined
  MacroNameTok: X_IMPL
  MacroDirective: MD_Define

  Defined Callback

Defined is called when the ‘defined’ operator is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.
Range | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range for the directive.

Example::

- Callback: Defined
  MacroNameTok: MACRO
  MacroDirective: (null)
  Range: ["D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:8:5", "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:8:19"]

  SourceRangeSkipped Callback

SourceRangeSkipped is called when a source range is skipped.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Range | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range skipped.

Example::

- Callback: SourceRangeSkipped
  Range: [":/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:8:2", ":/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:9:2"]

  If Callback

If is called when an #if is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
ConditionRange | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range for the condition.
ConditionValue | (true|false) | bool | The condition value.

Example::

- Callback: If
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:8:2"
  ConditionRange: ["D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:8:4", "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:9:1"]
  ConditionValue: false

  Elif Callback

Elif is called when an #elif is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
ConditionRange | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range for the condition.
ConditionValue | (true|false) | bool | The condition value.
IfLoc | “(file):(line):(col)” | SourceLocation | The location of the directive.

Example::

- Callback: Elif
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:10:2"
  ConditionRange: ["D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:10:4", "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:11:1"]
  ConditionValue: false
  IfLoc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:8:2"

  Ifdef Callback

Ifdef is called when an #ifdef is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.

Example::

- Callback: Ifdef
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-conditional.cpp:3:1"
  MacroNameTok: MACRO
  MacroDirective: MD_Define

  Ifndef Callback

Ifndef is called when an #ifndef is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.

Example::

- Callback: Ifndef
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-conditional.cpp:3:1"
  MacroNameTok: MACRO
  MacroDirective: MD_Define

  Else Callback

Else is called when an #else is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the else directive.
IfLoc | “(file):(line):(col)” | SourceLocation | The location of the if directive.

Example::

- Callback: Else
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:10:2"
  IfLoc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:8:2"

  Endif Callback

Endif is called when an #endif is seen.

Argument descriptions:
Argument Name | Argument Value Syntax | Clang C++ Type | Description
Loc | “(file):(line):(col)” | SourceLocation | The location of the endif directive.
IfLoc | “(file):(line):(col)” | SourceLocation | The location of the if directive.

Example::

- Callback: Endif
  Loc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:10:2"
  IfLoc: "D:/Clang/llvm/tools/clang/tools/extra/test/pp-trace/pp-trace-macro.cpp:8:2"

  Building pp-trace

To build from source:

1.  Read Getting Started with the LLVM System and Clang Tools Documentation for information on getting sources for LLVM, Clang, and Clang Extra Tools.

2.  Getting Started with the LLVM System and Building LLVM with CMake give directions for how to build. With sources all checked out into the right place the LLVM build will build Clang Extra Tools and their dependencies automatically.

•   If using CMake, you can also use the pp-trace target to build just the pp-trace tool and its dependencies.

CLANG-RENAME

  Contents

•   Clang-Rename

•   Using Clang-Rename

•   Vim Integration

•   Emacs Integration

    See also:

    clang-rename is a C++ refactoring tool. Its purpose is to perform efficient renaming actions in large-scale projects such as renaming classes, functions, variables, arguments, namespaces etc.

    The tool is in a very early development stage, so you might encounter bugs and crashes. Submitting reports with information about how to reproduce the issue to the LLVM bugtracker will definitely help the project. If you have any ideas or suggestions, you might want to put a feature request there.

  Using Clang-Rename

clang-rename is a LibTooling-based tool, and it’s easier to work with if you set up a compile command database for your project (for an example of how to do this see How To Setup Tooling For LLVM). You can also specify compilation options on the command line after –:

$ clang-rename -offset=42 -new-name=foo test.cpp -- -Imy_project/include -DMY_DEFINES ...

To get an offset of a symbol in a file run

$ grep -FUbo 'foo' file.cpp

The tool currently supports renaming actions inside a single translation unit only. It is planned to extend the tool’s functionality to support multi-TU renaming actions in the future.

clang-rename also aims to be easily integrated into popular text editors, such as Vim and Emacs, and improve the workflow of users.

Although a command line interface exists, it is highly recommended to use the text editor interface instead for better experience.

You can also identify one or more symbols to be renamed by giving the fully qualified name:

$ clang-rename -qualified-name=foo -new-name=bar test.cpp

Renaming multiple symbols at once is supported, too. However, clang-rename doesn’t accept both -offset and -qualified-name at the same time. So, you can either specify multiple -offset or -qualified-name.

$ clang-rename -offset=42 -new-name=bar1 -offset=150 -new-name=bar2 test.cpp

or

$ clang-rename -qualified-name=foo1 -new-name=bar1 -qualified-name=foo2 -new-name=bar2 test.cpp

Alternatively, {offset | qualified-name} / new-name pairs can be put into a YAML file:

---
- Offset:         42
  NewName:        bar1
- Offset:         150
  NewName:        bar2
...

or

---
- QualifiedName:  foo1
  NewName:        bar1
- QualifiedName:  foo2
  NewName:        bar2
...

That way you can avoid spelling out all the names as command line arguments:

$ clang-rename -input=test.yaml test.cpp

clang-rename offers the following options:

$ clang-rename --help
USAGE: clang-rename [subcommand] [options] <source0> [... <sourceN>]
OPTIONS:
Generic Options:
  -help                      - Display available options (-help-hidden for more)
  -help-list                 - Display list of available options (-help-list-hidden for more)
  -version                   - Display the version of this program
clang-rename common options:
  -export-fixes=<filename>   - YAML file to store suggested fixes in.
  -extra-arg=<string>        - Additional argument to append to the compiler command line
  -extra-arg-before=<string> - Additional argument to prepend to the compiler command line
  -i                         - Overwrite edited <file>s.
  -input=<string>            - YAML file to load oldname-newname pairs from.
  -new-name=<string>         - The new name to change the symbol to.
  -offset=<uint>             - Locates the symbol by offset as opposed to <line>:<column>.
  -p=<string>                - Build path
  -pl                        - Print the locations affected by renaming to stderr.
  -pn                        - Print the found symbol's name prior to renaming to stderr.
  -qualified-name=<string>   - The fully qualified name of the symbol.

  Vim Integration

You can call clang-rename directly from Vim! To set up clang-rename integration for Vim see clang-rename/tool/clang-rename.py.

Please note that you have to save all buffers, in which the replacement will happen before running the tool.

Once installed, you can point your cursor to symbols you want to rename, press <leader>cr and type new desired name. The <leader> key is a reference to a specific key defined by the mapleader variable and is bound to backslash by default.

  Emacs Integration

You can also use clang-rename while using Emacs! To set up clang-rename integration for Emacs see clang-rename/tool/clang-rename.el.

Once installed, you can point your cursor to symbols you want to rename, press M-X, type clang-rename and new desired name.

Please note that you have to save all buffers, in which the replacement will happen before running the tool.

•   genindex

•   search

AUTHOR
The Clang Team

COPYRIGHT
2007-2017, The Clang Team