我在OS X上使用了它并为我工作（也链接到ibresolv.dylib）

#include <arpa/inet.h>
#include <ifaddrs.h>
#include <resolv.h>
#include <dns.h>

- (NSString *) getDNSAddressesStr 
{
    NSMutableString *addressStr = [[NSMutableString alloc]initWithString:@"DNS Addresses \n"];

    res_state res = malloc(sizeof(struct __res_state));

    int result = res_ninit(res);

    if ( result == 0 )
    {    
        for ( int i = 0; i < res->nscount; i++ )
        {
            NSString *s = [NSString stringWithUTF8String :  inet_ntoa(res->nsaddr_list[i].sin_addr)];
            [addressStr appendFormat:@"%@\n",s];
            NSLog(@"%@",s);
        }
    }
    else 
        [addressStr appendString:@" res_init result != 0"];

    return addressStr;
    }
}