问如何确定接口名称

EN

getaddrinfo(argv[1], NULL, hints, &answ) //argv[1] it is host name
....
....
socket(tmp->ai_family, tmp->ai_socktype, tmp->ai_protocol) //tmp = answ->ai_next
....
....
/* filling the tcphdr struct */
send_frame->source = s_port;
send_frame->dest = d_port;
send_frame->seq = seq_num;
send_frame->ack_seq = ack_num;
send_frame->doff = 5;
send_frame->fin = 0;
send_frame->syn = 1;
send_frame->rst = 0;
send_frame->psh = 0;
send_frame->ack = 0;
send_frame->urg = 0;
send_frame->window = 0xffff;
send_frame->check = 0;
/* in this part I form a pseudo tcp header for checksum */
/* but for pseudo header i need a source ip address */
/* but I can not know before, what will be the source address */
/* and I can not form the pseudo header, because I do not know what my source address */
sendto(sock, send_frame, sizeof(struct tcphdr), 0, tmp->ai_addr, tmp->ai_addrlen);

    connect(sock, tmp->ai_addr, tmp->ai_addrlen);
    struct sockaddr_in addr;
    socklen_t len = sizeof(struct sockaddr_in);
    getsockname(sock, (struct sockaddr *)&addr, &len);
    printf("%s\n", inet_ntoa(addr.sin_addr));