在c ++套接字编程中由代理服务器连接到服务器时出错

Question

连接代码：

    cout << "connecting1\n";
    WSADATA wsadata;
    int iResult = WSAStartup (MAKEWORD(2,2), &wsadata );
    if (iResult !=NO_ERROR )
        printf("\nmyERROR at WSAStartup()\n");
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock == -1) {
        perror("error opening socket"); return -1;
    }
    struct sockaddr_in sin;
    sin.sin_port = htons(port);
    sin.sin_addr.s_addr = inet_addr(host.c_str());
    sin.sin_family = AF_INET;

    if (connect(sock, (struct sockaddr *)&sin, sizeof(sin)) == -1) {
        perror("error connecting to host"); return -1;
    }
    const int query_len = query.length() + 1; // trailing '\0'
    if (send(sock, query.c_str(), query_len, 0) != query_len) {
        perror("error sending query"); return -1;
    }

    const int buf_size = 1024 * 1024;
    while (true) {
        std::vector<char> buf(buf_size, '\0');
        const int recv_len = recv(sock, &buf[0], buf_size - 1, 0);

        if (recv_len == -1) {
            perror("error receiving response"); return -1;
        } else if (recv_len == 0) {
            std::cout << std::endl; break;
        } else {
            std::cout << &buf[0];           
            fprintf(fp, "%s", &buf[0]);
        }
    }

在没有代理的wifi中它工作正常，但是当我们使用代理服务器时，可以在chrome中访问net，但上面的代码打印

connecting1

error connecting to host

有什么问题？