Subject: cygwin 1.3.10 semctl fails, but does not set errno
From: Michael Potter <[email-masked]>
To: [email-masked]
Date: Mon, 3 Jun 2002 11:25:35 -0500 (CDT)

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ipc.h>
#include <sys/shm.h>

/* ----------------------------------------------------------------
** This program demostrates that semctl returns -1 (an error) but
** does not set errno (or at least sets it to 0).
**
** Compile this test program like this:
** gcc -o semctltest semctltest.c -lcygipc
**
** The problem is demostrated when you get this output:
** -> ./shmctltest
** shmctl failed with 0
**
** If you get:
** -> ./shmctltest
** shmget failed with 17
** Then you need to use ipcrm to remove the shared memory.
*/

int main(int argc, char *argv[])
{
   int shmid;
   int SaveErrno;
   struct shmid_ds shmid_ds;

   if ((shmid = shmget(508, 1024*1024, 0666|IPC_CREAT|IPC_EXCL)) == -1)
   {
      SaveErrno = errno;
      printf("shmget failed with %d\n", SaveErrno);
      exit(1);
   }

   shmid_ds.shm_perm.uid = getuid();
   shmid_ds.shm_perm.gid = getgid();
   shmid_ds.shm_perm.mode = 0666;

   if (shmctl(shmid, IPC_SET, &shmid_ds) == -1)
   {
      SaveErrno = errno;
      printf("shmctl failed with %d\n", SaveErrno);
      exit(1);
   }

   exit(0);
}

-- 
Michael Potter
LIDP Consulting Inc.

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