What's wrong with sem_init()?

[jsrig88]

I'm having a bit of an issue with this compiling in Linux with gcc. The command I am typing in is gcc -o <program name> <program name>.c. That has been working, even with these library-dependent data types and stuff, until I included sem_init in the middle.

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
        
/************************************************************************
* method:  int main()                                                   *
* purpose: to serve as the driving/starting method for the program      *
* returns: 0 to the operating system to signal normal completion        *
*                                                                       *
* approach:                                                             *
************************************************************************/
int main()
{
        /* the semaphores */
        sem_t lowercaseSemaphore; /* for the lowercase letters */
        sem_t capitalSemaphore;   /* for the capital letters */
        sem_t digitSemaphore;     /* for the digits */

        /* initializing all the semaphores basically to 1 */
        sem_init(&lowercaseSemaphore, 0, 1);
        sem_init(&capitalSemaphore, 0, 1);
        sem_init(&digitSemaphore, 0, 1);

        /* the three character buffers */
        char lowercase; /* for a lowercase letter */
        char capital;   /* for a capital letter */
        char digit;     /* for a digit 0-9 */

        return 0;
}

The error message ==

/tmp/ccChuvdk.o: In function `main':
<program name>.c:(.text+0x28): undefined reference to `sem_init'
<program name>.c:(.text+0x43): undefined reference to `sem_init'
<program name>.c:(.text+0x5e): undefined reference to `sem_init'
collect2: ld returned 1 exit status

What's going on here? I've checked the instructor's example, I've checked the man page for sem_init several times, and I've checked my code several times.

[tabstop]

The Linux man page says

Programs using the POSIX semaphores API must be compiled with cc -lrt to link against the real-time library, librt.

(by typing "man semaphores" -- edit, sorry: typing "man sem_overview", the "see also" at the bottom of the sem_init main page).

[nadroj]

These are linking errors, pass "-lpthread" to gcc.

[jsrig88]

I looked at that a little bit after reading your reply, and this seems to compile:
gcc -o <program name> <program name>.c -lrt. Is that the correct way to do it?