A question about an include file.

Could someone explain what the following line, which is taken from /usr/include/errno.h, means : extern void perror __P ((__const char* __s)); As I understand it, it means that perror is defined in an external file and returns a void type. But what are the __P, and __const ? And

Re: A question about an include file.

__P is basically a macro that lets the declaration work with both KR-style and ANSI C compilers. I haven't looked at it directly but it's something like #if (K_AND_R) #define __P(x) x #elif (ANSI_C) #define __P(x) #endif __const is likewise a macro, probably to work with compilers which don't