Why is this semaphore code failing?

#include <semaphore.h>


sem_t mutex;


int main (int argc, char * argv[])
{



sem_init (&mutex,0,1); 

}

I'm getting:

/tmp/ccAMFxDX.o: In function开发者_开发百科 `main':
programaservidor.c:(.text+0x86): undefined reference to `sem_init'
collect2: ld returned 1 exit status

Per the sem_init() man page

Link with -lrt or -pthread.

As in gcc your_code.c -lpthread -o your_code

As stated in the man page, you have to link with either -lrt or -pthread.

The relevant POSIX reference is:

http://www.opengroup.org/onlinepubs/9699919799/utilities/c99.html#tag_20_11_13