问题
My question is mainly about the fact that a C++ toolchain "understands" both C and C++, so if I feed some code with an extern "C" to a c++ toolchain I assume it can understand what to do with that; but what if I feed code with extern "C++" to a C toolchain ?
What is the expected behaviour ?
回答1:
If the compiler ALSO understands C++, it may accept it. If it's a pure C compiler it will object (just like it will on extern "C" as that syntax is not valid C - this is why it's typically enclosed with #ifdef __cplusplus or some such)
回答2:
It is supposed to not compile, it is not valid C syntax.
The standard approach to make C declarations in a header file work both in a C and C++ compiler is to rely on a preprocessor symbol that's only defined in a C++ compiler. Like this:
#ifdef __cplusplus
extern "C" {
#endif
// C declarations here
// ...
#ifdef __cplusplus
}
#endif
Every C++ compiler defines __cplusplus.
回答3:
extern "C++" is not valid C code, so a conforming C compiler must issue a diagnostic. There is no requirement that it not compile the code. Having issued a diagnostic, the compiler is free to do whatever its implementor decided was appropriate.
回答4:
If you wrote some other compiler with such option you can do this.
As answered by @Mats we have another procedure to achieve this is #ifdef __cplusplus.
Moreover what you are trying is error only.
来源：https://stackoverflow.com/questions/18288790/what-happens-if-i-use-extern-c-with-a-c-toolchain