How to use Glibc feature test macros?

Question

I'd line to use pthread_setname_np function if it's available. Code from the manpage:

   #define _GNU_SOURCE             /* See feature_test_macros(7) */
   #include <pthread.h>
   int pthread_setname_np(pthread_t thread, const char *name);
   int pthread_getname_np(pthread_t thread,
                          char *name, size_t len);

Is it safe to just do like that (no includes, no defines):

#ifdef _GNU_SOURCE
    pthread_setname_np(pthread_self(), "mythread");
#endif

Includes are not needed because the C++ #include <thread> that I use seems to pull pthreads. The _GNU_SOURCE is always enabled in libstdc++, and if it gets disabled - the code will still compile.

Am I missing something?

Did you read [feature_test_macros(7)](http://man7.org/linux/man-pages/man7/feature_test_macros.7.html) ? — Basile Starynkevitch, Oct 25 '16 at 11:41
@BasileStarynkevitch, yes. It's about controlling what the standard library provides. I'm interested in activating of a feature of my program depending on how the build was set up. — Velkan, Oct 25 '16 at 11:46
It seems this question is tag'd as `c` but the actual question discussed `c++`. These are different languages. Please pick one. — user3629249, Oct 26 '16 at 22:37
@user3629249, it's about `glibc`'s feature test macros. I wouldn't tag it with `c` or `c++` at all, but I figured that C pogrammers are more familiar with glibc and Linux (and there are more of C programmers in general). — Velkan, Oct 27 '16 at 06:36

P.P · Answer 1 · 2016-10-25T12:07:25.817

Is it safe to just do like that (no includes, no defines):

Yes. It's safe as long as you include <pthread.h> which provides the prototype for pthread_setname_np.

Includes are not needed because the C++ #include that I use seems to pull pthreads.

libc++ uses pthreads library underneath. So, it works with pthread.h. But that doesn't mean pthread.h isn't needed if you include <thread>. What if libc++ changes the underlying mechanism to implement threads? So, it's not safe to by pass pthread.h just because it happens to be available by other means.

How to use Glibc feature test macros?

1 Answers1