undefined reference

[zippo <zippo752001@comcast.net>]

I am getting a undefined reference error to this code. I don't see why. Any help would be great.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dvdread/dvd_reader.h>
#include <dvdread/ifo_types.h>
#include <dvdread/ifo_read.h>
#include <dvdread/nav_read.h>
#include <dvdread/nav_print.h>

int main() {

	ifo_handle_t *vmg_file;
	dvd_reader_t      *dvd;
		
	vmg_file = ifoOpen( dvd, 0 );
	
	//printf ("YAY %s", vmg_file);
	ifoClose( vmg_file );
}

$ gcc main.c -o rip
/tmp/cc8cLKIQ.o(.text+0x2b): In function `main':
: undefined reference to `ifoOpen'
/tmp/cc8cLKIQ.o(.text+0x39): In function `main':
: undefined reference to `ifoClose'
collect2: ld returned 1 exit status