Not sure why I am getting an undefine refence to gss_str_to_oid error

I am using gssapi in C for the first time. I am trying to reconstruct example on Oracle doc http://docs.oracle.com/cd/E19683-01/816-1331/sampleprogs-1/index.html. In my .c file I call gss_str_to_oid(&min_stat, &tok, oid); and get an undefined reference error. I included #include "gssapi.h" at the top of my .c file. In gssapi.h there is a function call

OM_uint32 KRB5_CALLCONV
gss_str_to_oid(
    OM_uint32 *,        /* minor_status */
    gss_buffer_t,       /* oid_str */
    gss_OID *); 

So what am I doing wrong? I thought that if you included #include "gssapi.h" it would give me access to function in gssapi. Both files are in my src folder. So what am I doing wrong. I am using eclipse and from what in my makefile under targets it says all: GSS-API. I am including most of my code below.

main

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <error.h>
#include <sys/stat.h>
#include <fcntl.h>

#include "gssapi.h"
#include "gssapi_ext.h"
#include "gss-misc.h"

/* global mech oid needed by display status, and acquire cred */
FILE *display_file;
gss_OID g_mechOid = GSS_C_NULL_OID;


void usage()
{
     fprintf(stderr, "Usage: gss-client [-port port] [-d]"
                        " [-mech mechOid] host service msg\n");
     exit(1);
}

static void parse_oid(char *mechanism, gss_OID *oid)
{
    char        *mechstr = 0, *cp;
    gss_buffer_desc tok;
    OM_uint32 maj_stat, min_stat;

    if (isdigit(mechanism[0])) {
        mechstr = malloc(strlen(mechanism)+5);
        if (!mechstr) {
            printf("Couldn't allocate mechanism scratch!\n");
            return;
        }
        sprintf(mechstr, "{ %s }", mechanism);
        for (cp = mechstr; *cp; cp++)
            if (*cp == '.')
                *cp = ' ';
        tok.value = mechstr;
    } else
        tok.value = mechanism;
    tok.length = strlen(tok.value);
      maj_stat = gss_str_to_oid(&min_stat, &tok, oid);
    if (maj_stat != GSS_S_COMPLETE) {
 //       display_status("str_to_oid", maj_stat, min_stat);
        return;
    }
    if (mechstr)
        free(mechstr);
}

int main(argc, argv)
     int argc;
     char **argv;
{
    /* char *service_name, *hostname, *msg; */
     char *msg;
     char service_name[128];
     char hostname[128];
     char *mechanism = 0;
     u_short port = 4444;
     int use_file = 0;
     OM_uint32 deleg_flag = 0, min_stat;

     display_file = stdout;

     /* Parse arguments. */

     argc--; argv++;
     while (argc) {
          if (strcmp(*argv, "-port") == 0) {
               argc--; argv++;
               if (!argc) usage();
               port = atoi(*argv);
           } else if (strcmp(*argv, "-mech") == 0) {
               argc--; argv++;
               if (!argc) usage();
               mechanism = *argv;
           } else if (strcmp(*argv, "-d") == 0) {
               deleg_flag = GSS_C_DELEG_FLAG;
          } else if (strcmp(*argv, "-f") == 0) {
               use_file = 1;
          } else
                break;
          argc--; argv++;
     }
     if (argc != 3)
          usage();

     if (argc > 1) {
                strcpy(hostname, argv[0]);
        } else if (gethostname(hostname, sizeof(hostname)) == -1) {
                        perror("gethostname");
                        exit(1);
        }


     if (argc > 2) {
        strcpy(service_name, argv[1]);
        strcat(service_name, "@");
        strcat(service_name, hostname);

     }

      msg = argv[2];

     if (mechanism)
         parse_oid(mechanism, &g_mechOid);

/*     if (call_server(hostname, port, g_mechOid, service_name,
                   deleg_flag, msg, use_file) < 0)
          exit(1);*/

/*
     if (g_mechOid != GSS_C_NULL_OID)
         (void) gss_release_oid(&min_stat, &gmechOid);
*/

     return 0;
}

gssapi.h

/* New for V2 */
OM_uint32 KRB5_CALLCONV
gss_str_to_oid(
    OM_uint32 *,        /* minor_status */
    gss_buffer_t,       /* oid_str */
    gss_OID *);  

You just can't include the header you have to link the library either dynamically or statically. Is there some dll, lib, so, etc you need to add to your project? Without makefile or your project setup been shown in your question; I think you will not receive a very clear answer. Just including header file isn't enough, the undefined is not a compilation error but a linker error, which means its missing a reference because you are not linking the library to your program.