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;
}
This uses realpath, so it works on FreeBSD. If you are using FreeBSD or another BSD-like operating system, you can also use getprogname:
/* For getprogname. */
#include <stdlib.h>
#include "call_realpath.h"

int main ()
{
    call_realpath (getprogname ());
    return 0;
}
On a system like Linux, which uses glibc (the GNU C library), the value of argv[0] is available in a global variable called program_invocation_name:
#include "call_realpath.h"

extern char * program_invocation_name;

int main ()
{
    call_realpath (program_invocation_name);
    return 0;
}
You can also find it from reading the file /proc/{number}/cmdline, where {number} is the process number, returned by getpid.
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