DNS 解析编程实例

Linux下常用的地址解析函数有:

    int res_query(const char *dname, int class, int type,
              unsigned char *answer, int anslen);

    int res_search(const char *dname, int class, int type,
              unsigned char *answer, int anslen);

一般编程中，有这两个就足够了，今天这里给大家共享一下libevent库中提供的另外一个函数：evdns_resolve_ipv4，如果大家在编程中常用libevent,那么下面的实例会很有用。
#cat dns_lookup.c

#include
#include
#include
#include
#include

#include
#include
#include

#include
#include

void usage(void)
{
    printf("USAGE: dns-lookup \n");
    exit(0);
}

void lookup_cb(int result, char type, int count, int ttl, void *addresses, void *arg)
{
    struct in_addr *addrs = addresses;
    int i;

    if (result != DNS_ERR_NONE)
    {
        printf("Error looking up address.\n");
    }
    else
    {
        for (i = 0; i < count; i++)
        {
            printf("[%i][%s]=[%s]\n", i, arg, inet_ntoa(addrs[i]));
        }
        printf("DNS lookup done.\n");
    }
    exit(0);
}

int main(int argc, char **argv)
{
    if (argc != 2)
        usage();

    event_init();
    evdns_init();
    evdns_resolve_ipv4(argv[1], 0, lookup_cb, argv[1]);
    event_dispatch();

    return (0);
}

#gcc dns_lookup.c -o dns_lookup -l event
#./dns_lookup
[0][]=[74.125.224.50]
[1][]=[74.125.224.48]
[2][]=[74.125.224.51]
[3][]=[74.125.224.52]
[4][]=[74.125.224.49]
DNS lookup done.