What's the purpose of #ifdef __cplusplus?

[Subsonics]

I've seen the following in numerous header files.

#ifdef __cplusplus
extern "C" {
#endif

// some declarations

#ifdef __cplusplus
}
#endif

Presumably if the code is compiled as C++ the 'extern "C"' bit get's included in the header, but that does that achieve?

[laserlight]

To ensure that the names declared in that portion of code have C linkage, and thus C++ name mangling is not performed.

[Subsonics]

Thank you!

[anduril462]

It tells the C++ compiler to use C-style linkage. It avoids name mangling any extern "C" function (which it normally uses to deal with function overloading), so regular C programs can use the functions too. More info here: In C++ source, what is the effect of extern "C"? - Stack Overflow

[std10093]

Another usage(the one that i have come in face with) of the

extern "C"
{
..
}

is that someone has written a library in C,but your project is in C++,then with this extern you can use the C library into your C++ project

[whiteflags]

That's not another usage, you're discussing the same thing everyone else is.