CODEWITHSUNDEEP
csemaphore
marymary
marymary

Reputation: 21

semaphore initialization in c

arg.val = 1;

    if (sem_id = semget(IPC_PRIVATE, 1, 0600 | IPC_CREAT) == -1 ){
            perror("Creating semaphore failed");
            exit(1);
    }
    else {
            printf("Creating a semaphore with ID: %d \n",sem_id);
            if (semctl(sem_id, 0, SETVAL, arg) == -1 ) {                       
                    perror("Initialization of semaphore failed\n");
                    exit(1);
            }
    }

I am trying to create and initialize a semaphore and when I am compiling my program it returns me:
"Initialization of semaphore failed :Identifier removed

Could you explain me the reason why this happens??

Upvotes: 2

Views: 989

Answers (2)

Adam Schmidt
Adam Schmidt

Reputation: 452

The operation == has a higher precedence than the operation =. I believe this means this means that sem_id is getting set to a true value. You should group the operation in the if statement.

if((sem_id = semget(IPC_PRIVATE, 1, 0600 | IPC_CREAT)) == -1){

Upvotes: 1

Peter G.
Peter G.

Reputation: 15114

if (sem_id = semget(IPC_PRIVATE, 1, 0600 | IPC_CREAT) == -1 )

is parsed (because == binds stronger than =)

if (sem_id = (semget(IPC_PRIVATE, 1, 0600 | IPC_CREAT) == -1) )

you probably want

if ((sem_id = semget(IPC_PRIVATE, 1, 0600 | IPC_CREAT)) == -1 )

Upvotes: 1

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