Use of resolv.h

问题

I'm trying to find out my DNS server address by reading it from resolv.h's _res struct. According to man 3 resolver the setup code should be.

#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>

extern struct state _res;

and then I just read out whatever I need. My problem is that trying to compile this I get

resolver.c:5:21: error: conflicting types for '__res_state'
extern struct state _res;
                    ^
/usr/include/resolv.h:251:16: note: expanded from macro '_res'
#define _res (*__res_state())
               ^
/usr/include/resolv.h:249:28: note: previous declaration is here
extern struct __res_state *__res_state(void) __attribute__ ((__const__));
                           ^
1 error generated.

by clang.

What am I doing wrong?

回答1:

You shouldn't declare _res yourself - resolv.h includes the right declaration (despite what the man page implies).

回答2:

#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>


int main() {

    // call this first
    res_init();

    // do something with this list it contains list of dns servers
    _res.nsaddr_list[0];

}

来源：https://stackoverflow.com/questions/11371965/use-of-resolv-h