C++ extern “C“

In C++, extern "C"it is a linkage specification , which tells the C++ compiler to process the declared function or variable in the linkage manner of C language. This declaration is mainly used when referencing libraries written in C language in C++ code.

The C++ compiler will adapt the function name (Name Mangling) during the compilation process , also known as name mangling , to support features such as function overloading . The so-called adaptation is to attach some additional information to the function name, such as parameter type and quantity, so that the correct function can be found when linking . Therefore, the form of the same function name compiled in C++ may be different from that compiled in C.

However, the C language does not support function overloading, so in the C language, the function name will not be adapted after compilation, and remains the original function name. Therefore, if you directly refer to a C function in C++, the linker may not be able to find the correct function due to name mangling.

extern "C"It was created to solve this problem. It tells the C++ compiler that the declared function or variable is written in C and should be linked as C, that is, without name mangling.

For example, if you have a C library file "c_library.h", you can reference it in C++ like this:

extern "C" {
    #include "c_library.h"
}

In this way, c_library.hall functions and global variables in will be linked in C language, and can be correctly referenced in C++ code.

Note that extern "C"it can be used not only to include entire header files, but also to single function or variable declarations, for example:

extern "C" void c_function();  // 声明一个C语言的函数

extern "C" int c_variable;  // 声明一个C语言的全局变量

Additionally, extern "C"it can be used with curly braces {} to include multiple C functions or variables:

extern "C" {
    void c_function1();
    void c_function2();
    int c_variable;
}

In this way, c_function1, c_function2and c_variablewill be linked in the C language.