F_SETPIPE_SZ undeclared

Question

I have included following headers:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

I have also tried to use

#define _GNU_SOURCE

before #include <unistd.h>, but it also does not help.

I try to use fcntl and pass it F_SETPIPE_SZ as second argument, but I keep getting this error message:

error: ‘F_SETPIPE_SZ’ undeclared (first use in this function)

I actually found out that I don't need this, but I'm just curious why I can't use it.

Thank you.

So here's solution, thanks to Chrono Kitsune: Put

 #define _GNU_SOURCE

before any includes.

Answer 1

So here's the solution, thanks to Chrono Kitsune:

Put

#define _GNU_SOURCE

before any includes.

You should also pay attention to Chrono Kitsune's other comment.

Answer 2

F_SETPIPE_SZ/F_GETPIPE_SZ are relatively recent. Older kernels (e.g. 2.6.32 as used in RHEL6) don't have them. If you look in /usr/include/linux/fcntl.h and these constants aren't defined, then this API isn't going to work and you'll have to find some way to bypass it in whatever you're building.