C- Semaphore sem_getvalue not returning what I'm expecting?

Question

I've been trying to get myself more acquainted with semaphores and was wondering why this code isn't printing the value I expect.

#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char * argv[]) {
    sem_t sem;
    sem_init(&sem, 0, 1);
    int value;
    sem_getvalue(&sem, &value);
    printf("%d\n",value);

    return 0;
}

It prints 0 for the value. But from my understanding it should be getting the value I initialized the semaphore with which is 1? I tried using a semaphore in some code with pthreads and I initialized the semaphore with a value of 1, but when I called the sem_getvalue function it was printing 32767. Am I missing something here? Thanks in advance.

Edit: sem_init and sem_getvalue both return -1

Edit: Solved. It appears unnamed semaphores aren't implemented on Mac.

Answer 1

I'm getting the output as expected. (i.e. 1)

try using linking with pthread library

gcc sema.c -lpthread

Answer 2

Edit: Solved. It appears unnamed semaphores aren't implemented on Mac.

POSIX semaphore is considered as deprecated on Mac OSX. So, it doesn't work on it as expected.