warning '"_POSIX_C_SOURCE" redefined' when include Python.h

[eugenebeast]

BPO	1045893
Nosy	@loewis

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2013-05-10.15:37:26.232>
created_at = <Date 2004-10-13.05:06:02.000>
labels = ['extension-modules', 'invalid']
title = 'warning \'"_POSIX_C_SOURCE" redefined\' when include Python.h'
updated_at = <Date 2013-05-10.15:37:26.232>
user = 'https://bugs.python.org/eugenebeast'

bugs.python.org fields:

activity = <Date 2013-05-10.15:37:26.232>
actor = 'Jonathan.Wakely'
assignee = 'none'
closed = True
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2004-10-13.05:06:02.000>
creator = 'eugene_beast'
dependencies = []
files = []
hgrepos = []
issue_num = 1045893
keywords = []
message_count = 5.0
messages = ['22666', '22667', '22668', '22669', '188842']
nosy_count = 3.0
nosy_names = ['loewis', 'eugene_beast', 'Jonathan.Wakely']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1045893'
versions = ['Python 2.3']

[eugenebeast]

"""
In file included from /usr/include/python2.3/Python.h:8,
from script.h:21,
from server.cpp:23:
/usr/include/python2.3/pyconfig.h:847:1: warning:
"_POSIX_C_SOURCE" redefined
In file included from
/usr/lib/gcc/i386-redhat-linux/3.4.0/../../../../include/c++/3.4.0/i386-redhat-linux/bits/os_defines.h:39,
from
/usr/lib/gcc/i386-redhat-linux/3.4.0/../../../../include/c++/3.4.0/i386-redhat-linux/bits/c++config.h:35,
from
/usr/lib/gcc/i386-redhat-linux/3.4.0/../../../../include/c++/3.4.0/iostream:44,
from server.cpp:18:
/usr/include/features.h:131:1: warning: this is the
location of the previous definition
""'

The above message is shown whenever program (extending
or embedding python with C/C++) using Python.h was
compilled.

OS: Fedora Core 2
compiller: GCC 3.4.0
libc: glibc-2.3
Python: 2.3.3

[loewis]

Logged In: YES
user_id=21627

This is a bug in your program. See

http://docs.python.org/api/includes.html

[eugenebeast]

Logged In: YES
user_id=126917

But why not made it more compliant in Python.h :

#ifndef _POSIX_C_SOURCE
#define _POSIX_C_SOURCE
#endif

???

[loewis]

Logged In: YES
user_id=21627

Python itself and Python extensions must be compiled with
precisely the same settings, so taking some other setting of
_POSIX_C_SOURCE may cause binary incompatibility.

If you include Python.h first, as you should,
_POSIX_C_SOURCE will not be defined, so the #ifndef should
not have any effect except in broken extension modules.

[JonathanWakely]

Insisting on including Python.h first is just broken.

GNU libc's /usr/include/features.h will override it anyway when _GNU_SOURCE is defined:

# undef _POSIX_C_SOURCE
# define _POSIX_C_SOURCE 200809L
# undef _XOPEN_SOURCE
# define _XOPEN_SOURCE 700

So if you define _GNU_SOURCE ( which happens automatically when using G++) the annoying defines in pyconfig.h are overridden anyway, so why not just only define them if not already defined?

Either you include Python.h first and its settings get ignored by glibc, or you don't include it first and you get annoying warnings.