nslookup程序(getaddrinfo和getnameinfo示例)

代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>

#define MAXLINE 64
int main(int argc, char **argv)
{
    struct addrinfo *p, *listp, hints;
    char buf[MAXLINE];
    int rc, flags;

    if (argc != 2) {
        fprintf(stderr, "usage: %s <domain name>\n", argv[0]);
        exit(0);
    }
    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_INET;  // 只用IPV4
    hints.ai_socktype = SOCK_STREAM;  // 只用TCP
    if ((rc = getaddrinfo(argv[1], NULL, &hints, &listp)) != 0) {
        fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(rc));
        exit(1);
    }

    flags = NI_NUMERICHOST;  // 展示数字而不是域名
    for (p = listp; p; p = p->ai_next) {  // 遍历结果链表
        getnameinfo(p->ai_addr, p->ai_addrlen, buf, MAXLINE, NULL, 0, flags);
        printf("%s\n", buf);
    }

    freeaddrinfo(listp);

    exit(0);
}

编译：

gcc nslookup.c -o nslook

运行：

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Reference:

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