[C][socket]getaddrinfo函数基本用法代码示例

使用getaddrinfo进行DNS解析

先上代码：

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <netdb.h>

int main()
{
    int ret, fd;
    char addrstr[] = "www.baidu.com";
    char portstr[] = "443";
    struct addrinfo* remote;
    struct addrinfo hints = {
        .ai_family = AF_UNSPEC,
        .ai_socktype = SOCK_STREAM,
        .ai_flags = AI_PASSIVE,
    };
    ret = getaddrinfo(addrstr, portstr, &hints, &remote);
    if (ret != 0)
    {
        perror("getaddrinfo");
        return -1;
    }
    printf("%s\n", inet_ntoa(((struct sockaddr_in*)(remote->ai_addr))->sin_addr));

    if ((fd = socket(remote->ai_addr->sa_family, SOCK_STREAM, 0)) == -1)
    {
        perror("socket");
        return -1;
    }

    if ((ret == connect(fd, remote->ai_addr, remote->ai_addrlen)) == -1)
    {
        perror("connect");
        return -1;
    }
    freeaddrinfo(remote);

    return 0;
}

test@test:~/my$ ./a.out 
180.101.49.12

getaddrinfo调用成功返回0，失败返回错误码，错误码可由gai_strerror(int errcode)转为含义字串。调用成功结果输出在第四个参数中，也就是代码中的&remote。

函数定义及结构体struct addrinfo如下：

int getaddrinfo(const char *node, const char *service,
                       const struct addrinfo *hints,
                       struct addrinfo **res);

void freeaddrinfo(struct addrinfo *res);

const char *gai_strerror(int errcode);

struct addrinfo {
               int              ai_flags;
               int              ai_family;
               int              ai_socktype;
               int              ai_protocol;
               socklen_t        ai_addrlen;
               struct sockaddr *ai_addr;
               char            *ai_canonname;
               struct addrinfo *ai_next;
           };

remote->ai_addr为struct sockaddr结构，可直接被套接字接口调用。