When I compile the following code:

#define _POSIX_C_SOURCE 200112L
#define _ISOC99_SOURCE
#define __EXTENSIONS__

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

int
main(int argc, char *argv[])
{
    char *symlinkpath = argv[1];
    char actualpath [PATH_MAX];
    char *ptr;
    ptr = realpath(symlinkpath, actualpath);
    printf("%s\n", ptr);
}

I get a warning on the line that contains the call to the realpath function, saying:

warning: assignment makes pointer from integer without a cast

Anybody know what's up? I'm running Ubuntu Linux 9.04