差值外部"C"表示"C". vs外部 [英] Difference extern"C" vs extern

问题描述

是对整个标头使用extern "C"指定符，还是对每个函数都指定extern是否存在区别?

Is there a difference whether I use the extern "C" specifier for the entire header, or specify extern for every function?

据我所知，没有，因为只有函数和变量可以在外部链接，所以当我在每个函数原型和extern变量之前使用extern说明符时，我无需使用全局声明！?

As far as I know, there is none, since only functions and variables can be linked externally, so when I use the extern specifier before every function prototype and extern variable, I have no need to use the global extern "C" declaration!?

示例A:

#ifdef __cplusplus
extern "C" {
#endif

void whatever(void);

#endif

示例B:

extern void whatever(void);

推荐答案

C ++文件中extern "C"的存在允许从C客户端调用程序代码调用特定的C ++函数.

The presence of extern "C" in a C++ file allows to call the particular C++ function from a C client caller code.

有什么区别?

很久很久以前，C编译器仅通过名称生成代码并处理函数. 它没有考虑参数.

A long, long time ago C-compilers generated code and addressed functions by name only. It didn't consider parameters.

在C ++中引入重载函数时，需要extern "C"为不同的函数指定相同的名称.例如void f()和void f(int)是C ++中的两个不同函数.

When overloaded functions were introduced in C++, extern "C" was required to specify the same name for different functions. For example void f() and void f(int) are two different functions in C++.

C ++编译器通过名称处理来完成此任务.它将一些信息添加到与函数参数有关的函数名称中.

The C++ compiler accomplished this via name-mangling. It adds some info to the function name related to the functions parameters.

extern "C"是对编译器的命令，用于引用较早的样式命名约定-无需弄乱".

extern "C" is a command to the compiler to "refer to the older style naming convention - without mangling".

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