linker error for ns_initparse

Question

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, nsbuf, 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

Educable

From some quick googling, it appears that these functions are considered internal and therefore deliberately not exported. They may be present in the static library. This is also probably version-dependent; there have been plenty of versions of the BIND API. jira.secondlife.com/browse/VWR-1598 and newsgroups-index.com/group/… – Shuck

Answer 1

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

Grebe

I have the same error as OP when compiling, but adding -lresolv did not solve it for me. My command is g++ -o test -x c++ -std=c++20 -lresolv ./test-resolv.cpp, any idea what I'm doing wrong? – Mickel

NM, I Solved my problem, it was pretty silly: the -l commands must come after the source reference (something about the order in which the linked loads libraries from -l to resolve references). – Mickel

Answer 2

I believe you need to add

#include <arpa/nameser.h> 

to your file

Dinorahdinosaur

This will not work since a header cannot define a reference. – Slush

Answer 3

I don't have enough reputation to reply to sdgfsdh, but Darakian is right, adding arpa/namesrv.h will help. Many implementations of libresolv use private symbols and make those symbols available using macros.

For example, macOS' nameser.h contains:

#define ns_initparse        res_9_ns_initparse

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