Get the full file name of the current executable on Unix

This C program prints the full file path to the current executable on Unix.

/* For printf. */
#include <stdio.h>
/* For realpath. */
#include <stdlib.h>
/* For PATH_MAX (the maximum length of a path). */
#include <sys/param.h>
/* For strerror. */
#include <string.h>
/* For errno. */
#include <errno.h>

static void
call_realpath (char * argv0)
{
    char resolved_path[PATH_MAX];

    if (realpath (argv0, resolved_path) == 0) { 
        fprintf (stderr, "realpath failed: %s\n", strerror (errno));
    } else {
        printf ("Program's full path is '%s'\n", resolved_path);
    }
}

int
main (int argc, char ** argv)
{
    printf ("Program called as '%s'\n", argv[0]);
    call_realpath (argv[0]);
    return 0;
}