On lots of C++ header files I read, I see constructs like this:
// Near the top, after the header guard:
#ifdef __cplusplus
extern "C" {
#endif
// ...
// Rest of header file
// ... And at the bottom..., often right before the closing #ifdef for the header guard:
#ifdef __cplusplus
}
#endif

What are they for?

Question

On lots of C++ header files I read, I see constructs like this:
// Near the top, after the header guard:
#ifdef __cplusplus
extern "C" {
#endif
// ...
// Rest of header file
// ... And at the bottom..., often right before the closing #ifdef for the header guard:
#ifdef __cplusplus
}
#endif

What are they for?

espex · Answer

It hides certain code from the C compilers which enables you to share libraries without confusing the compiler. The wrapped section will only be visible IF the compiler is defined as a C++ compiler.