iOS模拟器中的基本套接字编程

Question

我正在学习Beej的套接字教程为什么下面对socket的调用在iPhone模拟器中不起作用

    int status;
    struct addrinfo hints;
    struct addrinfo *servinfo;
    char ipstr[INET6_ADDRSTRLEN];
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;
    if ((status = getaddrinfo("www.yahoo.com", 
                              "80", 
                              &hints, 
                              &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo error: %sn", gai_strerror(status));
        exit(1);
    }
    for(struct addrinfo *p = servinfo; p != NULL; p = p->ai_next) {
        void *addr;
        char *ipver;
        if (p->ai_family == AF_INET) {
            struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
            addr = &(ipv4->sin_addr);
            ipver = "IPv4";
        } else {
            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
            addr = &(ipv6->sin6_addr);
            ipver = "IPv6";
        }
        inet_ntop(p->ai_family, addr, ipstr, sizeof(ipstr));
        printf("  %s: %sn", ipver, ipstr);
        int socketfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
        if (socketfd)
            printf("errno: %dn", errno);
    }
    freeaddrinfo(servinfo);

上述代码的输出为：

  IPv4: 72.30.38.140
  errno: 2
  IPv4: 72.30.2.43
  errno: 2

errno 2为No such file or directory。我不知道该怎么解释。

Answer 1

错误在这一行：

if (socketfd) {

这应该是：

if (socketfd == -1) {

由于socket()在出错时返回-1，而在成功时返回0（如前所述：https://stackoverflow.com/a/1879234/22471)