linker error for ns_initparse

Here the code

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <resolv.h>

int main (int argc, char *argv[])
{
    u_char nsbuf[4096];
    char dispbuf[4096];
    ns_msg msg;
    ns_rr rr;
    int i, j, l;

    if (argc < 2) {
        printf ("Usage: %s <domain>[...]\n", argv[0]);
        exit (1);
    }

    for (i = 1; i < argc; i++) {
        l = res_query (argv[i], ns_c_any, ns_t_mx, nsbuf, sizeof (nsbuf));
        if (l < 0) {
            perror (argv[i]);
        } else {
#ifdef USE_PQUERY

/* this will give lots of detailed info on the request and reply */

            res_pquery (&_res, nsbu开发者_StackOverflow社区f, l, stdout);
#else

/* just grab the MX answer info */

            ns_initparse (nsbuf, l, &msg);
            printf ("%s :\n", argv[i]);
            l = ns_msg_count (msg, ns_s_an);
            for (j = 0; j < l; j++) {
                ns_parserr (&msg, ns_s_an, j, &rr);
                ns_sprintrr (&msg, &rr, NULL, NULL, dispbuf, sizeof (dispbuf));
                printf ("%s\n", dispbuf);
            }
#endif
        }
    }

    exit (0);
}

I compile it as

gcc dns.c -lresolv

and I get the following linker error

In function main': dns.c:(.text+0xd5): undefined reference to__ns_initparse' dns.c:(.text+0x130): undefined reference to __ns_parserr' dns.c:(.text+0x16a): undefined reference to__ns_sprintrr'

Help

Linking with the resolver library helped fixed his issue for me, I added -lresolv to my compilation command.

I believe you need to add

#include <arpa/nameser.h> 

to your file