The issue in the Subject line came up in connection with an emacs bug
report.
Here's a test case:
$ cat test.c
#define _GNU_SOURCE
#include <stdlib.h>
int
main ()
{
aligned_alloc (1, 1);
}
$ gcc test.c -Wimplicit-function-declaration
test.c: In function ‘main’:
test.c:7:3: warning: implicit declaration of function ‘aligned_alloc’
The cause is that the declaration of aligned_alloc in stdlib.h is
guarded by #if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L; but
defining _GNU_SOURCE causes __ISO_C_VISIBLE to be defined as 1999.
Here's an excerpt from /usr/include/sys/cdefs.h showing how this happens:
/* Deal with _GNU_SOURCE, which implies everything and the kitchen sink */
#ifdef _GNU_SOURCE
[...]
#define _XOPEN_SOURCE 700
[...]
#endif
[...]
#if _XOPEN_SOURCE - 0 >= 700
[...]
#define _POSIX_C_SOURCE 200809
[...]
#endif
[...]
#if _POSIX_C_SOURCE >= 200809
[...]
#define __ISO_C_VISIBLE 1999
[...]
#endif /* _POSIX_C_SOURCE */
According to the discussion of the emacs bug I mentioned, Linux and
FreeBSD don't have this issue. Should Cygwin's headers be changed to
conform to those other platforms?
Ken
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