Linking to POSIX semaphores

[Andi Hellmund]

Hi Peter,

my man page says to link to librt _or_ libpthread. libpthread finally
defines the symbols sem_open and sem_unlink.

Andi

Peter Rockett wrote:
> I am trying to use POSIX named semaphores. Stripping it down, if I compile
> the program:
>
> #include <fcntl.h>
> #include <sys/stat.h>
> #include <semaphore.h>
>
> int main()
> {
>        sem_open("Sem1", O_CREAT, S_IRWXU, 0);
>        sem_unlink("Sem1");
>        return 0;
> }
>
> and link it to /usr/lib/librt.a (which the Linux man pages say is the
> necessary library), I get a link error saying that sem_open() and
> sem_unlink() are unresolved. Looking inside librt.a using the nm utility, I
> cannot find any reference to the POSIX semaphores. Am I doing something
> dumb? Where do I find the implementations of the POSIX semaphores? Am I
> misinterpreting the man pages somehow?
>
> (I am using Ubuntu 9.1 with gcc-4.4.1.)
>
> Peter
>
>
>