C++

C++ TutorialBasic input/output in c++C++ AlignmentC++ Argument Dependent Name LookupC++ Arithmitic MetaprogrammingC++ ArraysC++ Atomic TypesC++ AttributesC++ autoC++ Basic Type KeywordsC++ Bit fieldsC++ Bit ManipulationC++ Bit OperatorsC++ Build SystemsC++ C incompatibilitiesC++ C++11 Memory ModelC++ Callable ObjectsC++ Classes/StructuresC++ Client server examplesC++ Common compile/linker errors (GCC)C++ Compiling and BuildingC++ Concurrency with OpenMPC++ Const CorrectnessC++ const keywordC++ Constant class member functionsC++ constexprC++ ContainersC++ Copy ElisionC++ Copying vs AssignmentC++ Curiously Recurring Template Pattern (CRTP)C++ Date and time using chrono headerC++ Debugging and Debug-prevention Tools & TechniquesC++ decltypeC++ Digit separatorsC++ EnumerationC++ ExceptionsC++ Explicit type conversionsC++ Expression templatesC++ File I/OC++ Floating Point ArithmeticC++ Flow ControlC++ Fold ExpressionsC++ Friend keywordC++ function call by value vs. call by referenceC++ Function OverloadingC++ Function Template OverloadingC++ Futures and PromisesC++ Header FilesC++ Implementation-defined behaviorC++ Inline functionsC++ Inline variablesC++ IterationC++ IteratorsC++ KeywordsC++ LambdasC++ Layout of object typesC++ Linkage specificationsC++ LiteralsC++ LoopsC++ Memory managementC++ MetaprogrammingC++ Move SemanticsC++ mutable keywordC++ MutexesC++ NamespacesC++ Non-Static Member FunctionsC++ One Definition Rule (ODR)C++ Operator OverloadingC++ operator precedenceC++ OptimizationC++ Overload resolutionC++ Parameter packsC++ Perfect ForwardingC++ Pimpl IdiomC++ PointersC++ Pointers to membersC++ PolymorphismC++ PreprocessorC++ ProfilingC++ RAII: Resource Acquisition Is InitializationC++ Random number generationC++ Recursive MutexC++ Refactoring TechniquesC++ ReferencesC++ Regular expressionsC++ Resource ManagementC++ Return Type CovarianceC++ Returning several values from a functionC++ RTTI: Run-Time Type InformationC++ Scopes



C++ Linkage specifications

From WikiOD

A linkage specification tells the compiler to compile declarations in a way that allows them to be linked together with declarations written in another language, such as C.

Syntax[edit | edit source]

  • extern string-literal { declaration-seq(opt) }
  • extern string-literal declaration

Remarks[edit | edit source]

The standard requires all compilers to support extern "C" in order to allow C++ to be compatible with C, and extern "C++", which may be used to override an enclosing linkage specification and restore the default. Other supported linkage specifications are implementation-defined.

Signal handler for Unix-like operating system[edit | edit source]

Since a signal handler will be called by the kernel using the C calling convention, we must tell the compiler to use the C calling convention when compiling the function.

volatile sig_atomic_t death_signal = 0;
extern "C" void cleanup(int signum) {
    death_signal = signum;
}
int main() {
    bind(...);
    listen(...);
    signal(SIGTERM, cleanup);
    while (int fd = accept(...)) {
        if (fd == -1 && errno == EINTR && death_signal) {
            printf("Caught signal %d; shutting down\n", death_signal);
            break;
        }
        // ...
    }
}

Making a C library header compatible with C++[edit | edit source]

A C library header can usually be included into a C++ program, since most declarations are valid in both C and C++. For example, consider the following foo.h:

typedef struct Foo {
    int bar;
} Foo;
Foo make_foo(int);

The definition of make_foo is separately compiled and distributed with the header in object form.

A C++ program can #include <foo.h>, but the compiler will not know that the make_foo function is defined as a C symbol, and will probably try to look for it with a mangled name, and fail to locate it. Even if it can find the definition of make_foo in the library, not all platforms use the same calling conventions for C and C++, and the C++ compiler will use the C++ calling convention when calling make_foo, which is likely to cause a segmentation fault if make_foo is expecting to be called with the C calling convention.

The way to remedy this problem is to wrap almost all the declarations in the header in an extern "C" block.

#ifdef __cplusplus
extern "C" {
#endif

typedef struct Foo {
    int bar;
} Foo;
Foo make_foo(int);

#ifdef __cplusplus
}  /* end of "extern C" block */
#endif

Now when foo.h is included from a C program, it will just appear as ordinary declarations, but when foo.h is included from a C++ program, make_foo will be inside an extern "C" block and the compiler will know to look for an unmangled name and use the C calling convention.

Credit:Stack_Overflow_Documentation