On 2/2/2016 5:27 PM, Ken Brown wrote:
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?
Paul Eggert says they should:
Defining _GNU_SOURCE should make aligned_alloc visible regardless of whether -std=c99 is specified. This is because defining _GNU_SOURCE means, "Make GNU symbols visible even when compiling pedantically." This is OK, since the C standard says the behavior is undefined whenever the user defines a reserved symbol like _GNU_SOURCE.
Ken -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
