semaphore initialization

Question

I have a semaphore that I tried to change the value of and it fails. After reading the man page I learned that if the value is less than 0 and you use SETVAL it will fail (I wasn't initializing it). But when I initialize it I get "identifier removed" when I call perror(). I am not sure if it is referring to the SETALL or the union.

My initialization looks like this:

union semun argument; 
unsigned short values[1]; 
values[0] = 1; 
argument.array = values; 
int retVal;

//INITIALIZE our semaphore
if(retVal = semctl(semId, 0, SETALL, argument) == -1)
{
    perror("semaphore INITIALIZATION failed\n");
    exit(1);
}

I have my union declared just like the man page and several other websites do and I have a check after semget() to make sure it returns a semaphore so I know that part is working correctly. If anyone could tell me where I am going wrong I would greatly appreciate it.

Also if anyone could please explain the reason behind my error so that I can learn from my mistake that would be most helpful.

Thanks

UPDATE: apparently it did not like the == -1 so I changed it to < 0 and it worked fine really weird I dunno thanks for all the responses though

Answer 1

Probably you missed to initialize semId prior to the call to semctl().

Try to add the folliwing:

int semId = -1;

...

semId = semget(IPC_PRIVATE, 1, IPC_CREAT);
if (-1 == semId)
   perror("semget() failed");
else {
/* Your call to semctl() */
}