a strange question about "semget"

iclinux · 06-15-2005, 12:59 AM

hi,there,

I'm now using HP-UX, and want to find some help.
My question is :
I create a semaphore, that's ok. Then I create it again, and a error occurs, but errno is 0. I don't know why. Have you ever gotten this problem?

Best Regards,
iclinux

Code:

    semid=semget(0x12345678,1,0777|IPC_CREAT|IPC_EXCL);
    if (semid == -1) return;
 
    semid=semget(0x12345678,1,0777|IPC_CREAT|IPC_EXCL);
    if (semid == -1)
    {
        printf("errno is [%d]\n",errno); // strange, errno is 0, why??
        if (errno == EEXIST)
        {
            semid=semget(key,1,0);
            return true;
        }
        else
        {
            return false;
        }
    }

Dark_Helmet · 06-15-2005, 08:58 PM

I can't give you an answer for why errno is 0, because from what I read, it should be equal to EEXIST (assuming EEXIST is not defined to be 0). From the man page for semget():

Code:

RETURN VALUE
       If successful, the return value will be the semaphore set identifier (a
       nonnegative integer), otherwise -1 is returned, with  errno  indicating
       the error.

ERRORS
       On failure errno will be set to one of the following:

       ...

       EEXIST     A semaphore set exists for key and semflg was asserting both
                  IPC_CREAT and IPC_EXCL.

Tinkster · 06-15-2005, 11:58 PM

Moved: This thread is more suitable in "Other *nix" since it's not a linux-question, and has been moved accordingly to help your thread/question get the exposure it deserves.