c++ - 我们可以在没有#ifdef __cplusplus 的情况下在C 文件中使用extern "C"吗？

Question

为什么不应该为需要定义为 C 函数的函数指定 extern "C"？将文件编译为 C 源代码时，会对编译器产生什么影响？

如果对 C 编译器没有影响，难道我们不能像下面那样通过删除 #ifdef __cplusplus 检查在头文件中定义一个函数吗？

extern "C" {
    int MyFunc();
}

An answer to another question说需要 #ifdef，但我不明白为什么:

Regarding #2: __cplusplus will be defined for any compilation unit that is being run through the C++ compiler. Generally, that means .cpp files and any files being included by that .cpp file. The same .h (or .hh or .hpp or what-have-you) could be interpreted as C or C++ at different times, if different compilation units include them. If you want the prototypes in the .h file to refer to C symbol names, then they must have extern "C" when being interpreted as C++, and they should not have extern "C" when being interpreted as C -- hence the #ifdef __cplusplus checking.

Answer 1

构造 extern "C" 是一个 C++ 构造，C 编译器无法识别。通常，它会发出语法错误消息。

一个常见的技巧是定义一个宏，例如 EXTERN_C，根据您是使用 C 还是 C++ 编译，它会扩展为不同的东西。例如:

在公共(public)头文件中:

#ifdef __cplusplus
#define EXTERN_C extern "C" {
#define EXTERN_C_END }
#else
#define EXTERN_C
#define EXTERN_C_END
#endif

在其他文件中:

EXTERN_C
int MyFunc(void);
EXTERN_C_END