Do I need an extern “C” block to include standard POSIX C headers?

Question

Do I need an extern \"C\" {} block to include standard C headers in a C++ program. Only consider standard C headers which do not have counterparts in C++.

Answer 1

The system C headers usually already include a extern "C" block, guarded by #ifdef __cplusplus. This way the functions automatically get declared as extern "C" when compiled as C++ and you don't need to do that manually.

For example on my system unistd.h and fcntl.h start with __BEGIN_DECLS and end with __END_DECLS, which are macros defined in sys/cdefs.h:

/* C++ needs to know that types and declarations are C, not C++.  */
#ifdef   __cplusplus
# define __BEGIN_DECLS  extern "C" {                                            
# define __END_DECLS }
#else
# define __BEGIN_DECLS
# define __END_DECLS
#endif