MAP_ANONYMOUS with C99 standard

Question

I have an application that uses the mmap system call, I was having an issue getting it to compile for hours looking as to why I was getting MAP_ANON and MAP_ANONYMOUS were undec

Answer 1

You probably want -std=gnu99 instead of -std=c99. C99 mode explicitly disables (most) GNU extensions.

I wrote a simple test:

#include <sys/mman.h>

int a = MAP_ANONYMOUS;

In C99 mode, it doesn't find the value:

$ gcc -std=c99 -c d.c
d.c:3:9: error: ‘MAP_ANONYMOUS’ undeclared here (not in a function)

Whereas in Gnu99 mode, it does:

$ gcc -std=gnu99 -c d.c