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Re: Linking to POSIX semaphores
- From: Andi Hellmund <mail at andihellmund dot com>
- To: p dot rockett at sheffield dot ac dot uk
- Cc: gcc-help at gcc dot gnu dot org
- Date: Tue, 03 Nov 2009 22:16:19 +0100
- Subject: Re: Linking to POSIX semaphores
- References: <000801ca5cc0$5ec1b5f0$1c4521d0$@rockett@shef.ac.uk>
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
>
>
>