Why won't sys/stat.h define ino_t with -std=c1x?

Question

I'm experiencing a strange problem with some C code I am writing. Consider the following code:

#include <sys/stat.h>
ino_t inode;

According to POSIX.1-2008, the header file <sys/stat.h> defines ino_t¹:

The <sys/stat.h> header shall define the blkcnt_t, blksize_t, dev_t, ino_t, mode_t, nlink_t, uid_t, gid_t, off_t, and time_t types as described in <sys/types.h>.

This happens when I try to compile the source code above places in a file test.c on my Linux system:

$ cat test.c
#include <sys/stat.h>
ino_t inode;
$ uname -srm
Linux 3.8.0-26-generic x86_64
$ lsb_release -d
Description:    Ubuntu 13.04
$ gcc -c test.c
$ gcc -std=c90 test.c
test.c:2:1: error: unknown type name 'ino_t'
$ gcc -std=c99 test.c     
test.c:2:1: error: unknown type name 'ino_t'
$ gcc -std=c1x test.c
test.c:2:1: error: unknown type name 'ino_t'

Why is the definition of ino_t not revelead when I specify any -std option?

Answer 1

My manual page of fstat says to also include sys/types.h, and that solves the problem for me. The definition of ino_t in sys/stat.h is protected with the feature macros __USE_XOPEN and __USE_XOPEN2K. The definition in sys/types.h is not protected that way.

The manual page also says to include unistd.h, but that wasn't necessary to solve your problem.

According to the manual page of feature_test_macros:

__STRICT_ANSI__ ISO Standard C. This macro is implicitly defined by gcc(1) when invoked with, for example, the -std=c99 or -ansi flag.

I guess this means that any XOPEN features are also switched off. I could however not find any description of that.

P.S. It seems R.. (see below) feels that this is described also in the manual page of feature_test_macros, but my limited brain is not able to find the exact wording, so I'd like to leave that as an exercise to the reader. If it were described anywhere, then I would expect it in that manual page indeed.

Beware that the gist of this answer is as follows:

Thou shall include all include files mentioned in a manual page and not try to reverse engineer which ones may not be needed.