use_getaddrinfo.c

#include <stdio.h>              //printf
#include <string.h>             //memset
#include <unistd.h>             //close

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


static int tcp_connect(const char *pAddr, const char *pService)
{
    struct addrinfo hints;
    struct addrinfo *ainfo = NULL;
    int sock = -1;

    //IPアドレス取得
    memset(&hints, 0, sizeof(hints));
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_family = AF_INET;

    int ret = getaddrinfo(pAddr, pService, &hints, &ainfo);
    if (ret == 0) {
        struct addrinfo *rp;
        for (rp = ainfo; rp != NULL; rp = rp->ai_next) {
            sock = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
            if (sock < 0) {
                fprintf(stderr, "fail: sock\n");
                goto ERR_EXIT;
            }

            struct sockaddr_in *in = (struct sockaddr_in *)rp->ai_addr;
            fprintf(stderr, "addr : %s\n", inet_ntoa(in->sin_addr));
            ret = connect(sock, rp->ai_addr, rp->ai_addrlen);
            if (ret == 0) {
                //接続OK
                fprintf(stderr, "connected\n");
                break;
            }
        }
        if (rp == NULL) {
            goto ERR_EXIT;
        }
    } else {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(ret));
    }

ERR_EXIT:
    freeaddrinfo(ainfo);
    return sock;
}


int main(void)
{
    int sock = tcp_connect("www.yahoo.co.jp", "443");
    printf("socket=%d\n", sock);
    close(sock);

    return 0;
}