Comments on: _POSIX_C_SOURCE

By: Dan

Dan — Mon, 24 Nov 2008 03:17:06 +0000

The problem is that _POSIX_C_SOURCE is stupid, and doesn’t mean “I need POSIX features”. It means “I need POSIX features and I *don’t* need non-POSIX features. Basically this means that you only use _POSIX_C_SOURCE when you want to treat all platforms as being completely identical. If you are using autoconf, then pretty much by definition you don’t want to use _POSIX_C_SOURCE. (Yes, this means _POSIX_C_SOURCE is completely useless in the real world. It’s not meant for the real world, it’s meant for POSIX-compliance test suites.)

If you get a “not defined” warning on linux when you remove _POSIX_C_SOURCE, then set _GNU_SOURCE instead.

By: Jan Hauffa

Jan Hauffa — Sun, 23 Nov 2008 18:13:09 +0000

On my MacOS 10.5 system, sys/cdefs.h contains a few lines that look like this:

#if defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE == xyz

This only works if _POSIX_C_SOURCE has a value.

http://opengroup.org/onlinepubs/009695399/functions/xsh_chap02_02.html

The above link suggests that _POSIX_C_SOURCE should be defined to have the value 200112L.

By: meh

meh — Sun, 23 Nov 2008 16:52:59 +0000

The compilation is stopping on a line like

#if defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE == 1

Try changing your #define to something like

#define _POSIX_C_SOURCE 1

which is probably what you wanted in the first place.

By: Christian Kellner

Christian Kellner — Sun, 23 Nov 2008 14:09:32 +0000

“_POSIX_C_SOURCE means ‘I want to use POSIX and I don’t want to use any *non*-POSIX calls?’”

I guess not only on OSX, but on all compliant POSIX sources. From the spec: “Additional symbols not required or explicitly permitted by IEEE Std 1003.1-2001 to be in that header shall not be made visible, except when enabled by another feature test macro.”

I guess on OSX that “enabled by another feature test macro” thing is the “_DARWIN_C_SOURCE” macro.

By: Thomas Thurman

Thomas Thurman — Sun, 23 Nov 2008 13:33:55 +0000

What, so on OS X, _POSIX_C_SOURCE means “I want to use POSIX and I don’t want to use any *non*-POSIX calls?”

By: Lukáš 'Spike' Polívka

Lukáš 'Spike' Polívka — Sun, 23 Nov 2008 13:23:03 +0000

Is this your answer?

http://developer.apple.com/documentation/Darwin/Reference/ManPages/man5/compat.5.html