如何使用winsock2连接到本地主机

Question

我编写这个程序是为了与侦听端口 27015 的服务器进行内部通信。但是来自 connect() 的返回值给了我错误 10047。创建套接字没有问题，getaddrinfo() 返回不是错误。不知道为什么socket连接不上，会不会是network-byte和host-byte一致的问题？

#include <winsock2.h>
#include <windows.h>
#include <iostream>
#include <Ws2tcpip.h>
#include <iphlpapi.h>
#define DEFAULT_PORT "27015"
using namespace std;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,PSTR szCmdLine, int iCmdShow) {
    WSADATA wsaData;
    // Initialize Winsock version 2.2
    int ret;
    // holds server info//
    if (ret = WSAStartup(MAKEWORD(2,2), &wsaData) != 0){
        std::cout << "WSAStartup failed with error %ld\n", WSAGetLastError());
        return 0;
    }
    else{
        cout << "The current status is:" << wsaData.szSystemStatus << "\n";
    }
      
    // Setup Winsock communication code here
    struct addrinfo *result = NULL, *ptr = NULL, hints;
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
       
    memset(&hints, 0, sizeof(hints));
    int iResult = getaddrinfo("localhost", DEFAULT_PORT, &hints, &result);
    if (iResult != 0) {
        printf("getaddrinfo failed: %d\n", iResult);
        WSACleanup();
        return 1;
    }
    SOCKET Sending_socket; 
      
    Sending_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (Sending_socket == INVALID_SOCKET){
        cout << "socket error\n";
        WSACleanup();
        return 0;
    }
     
    // now we connect to the server ,RetCode=return of connect()
    int RetCode = connect(Sending_socket, result->ai_addr, (int)result->ai_addrlen);
    if (RetCode != 0) {
        int num_attempt = 0;
        while (RetCode != 0 && num_attempt != 100){
            printf("Error at socket(): %ld\n", WSAGetLastError());
            RetCode = connect(Sending_socket, result->ai_addr, (int)result->ai_addrlen);
            num_attempt++;
        }        
    }
    else {
        cout << "connect okay \n";
    }
    int them ;
    closesocket(Sending_socket);
    // When your application is finished call WSACleanup
    them = WSACleanup();
    // making sure to cleanup
    if (them != 0){
        cout << "WSACleanup failed with error " << WSAGetLastError();
        // and exit
        return 1;
    }
    return 1;
}

Answer 1

错误 10047 是 WSAEAFNOSUPPORT，当您尝试为 connect() 提供一个 IP 地址，其系列不受正在连接的套接字支持时，即通过将 AF_INET 地址传递给 AF_INET6 套接字时，会发生错误，或AF_INET6 地址到AF_INET 套接字。在这种情况下，后者正在发生。

发生这种情况的原因是因为您拨打 memset(&hints, 0, sizeof(hints)); 的位置有误！

您声明了 hints 变量并且不要最初将其归零，然后您开始为AF_INET 套接字填充它，但随后您使用memset() 将其归零就在你把它交给getaddrinfo()之前。所以getaddrinfo() 看到hints.ai_family 的值为0 (AF_UNSPEC)，因此允许getaddrinfo() 为"localhost" 返回一个IPv4 或/和一个IPv6 地址。最有可能的是，getaddrinfo() 在输出列表的前面输出了一个AF_INET6 地址（请记住，getaddrinfo() 输出一个以空结尾的链接列表解析的 IP 地址）。

然后您继续使用硬编码的AF_INET 作为套接字系列创建一个新套接字，而不是使用来自result->ai_family 的值，然后将result->ai_addr 分配给connect()，但失败并出现错误如果该 IP 地址是 AF_INET6 地址而不是 AF_INET 地址，则为 10047。

话虽如此，请尝试更多类似的东西：

#include <winsock2.h>
#include <windows.h>
#include <iostream>
#include <Ws2tcpip.h>
#include <iphlpapi.h>

#define DEFAULT_PORT "27015"

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
    WSADATA wsaData;
    int ret;

    // Initialize Winsock version 2.2
    ret = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (ret != 0)
    {
        std::cout << "WSAStartup failed with error " << ret << "\n";
        return 0;
    }

    std::cout << "The current status is:" << wsaData.szSystemStatus << "\n";
      
    // Setup Winsock communication code here
    struct addrinfo *result = NULL, *ptr = NULL, hints;
    memset(&hints, 0, sizeof(hints)); // <-- MOVED HERE!!!
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
       
    ret = getaddrinfo("localhost", DEFAULT_PORT, &hints, &result);
    if (ret != 0)
    {
        std::cout << "getaddrinfo failed: " << ret << "\n";
        WSACleanup();
        return 0;
    }

    SOCKET Sending_socket = INVALID_SOCKET;

    for (int num_attempt = 0; num_attempt < 100; ++num_attempt)
    {
        Sending_socket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
        if (Sending_socket == INVALID_SOCKET)
        {
            std::cout << "socket failed: " << WSAGetLastError() << "\n";
            freeaddrinfo(result);
            WSACleanup();
            return 0;
        }

        // now we connect to the server
        ret = connect(Sending_socket, result->ai_addr, (int)result->ai_addrlen);
        if (ret == 0)
            break;

        std::cout << "Error at socket(): " << WSAGetLastError() << "\n";

        closesocket(Sending_socket);
        Sending_socket = INVALID_SOCKET;
    }

    /* alternatively:

    SOCKET Sending_socket = INVALID_SOCKET;

    for (int num_attempt = 0; Sending_socket == INVALID_SOCKET && num_attempt < 100; ++num_attempt)
    {
        for(ptr = result; ptr != NULL; ptr = ptr->ai_next)
        {
            Sending_socket = socket(ptr->ai_family, ptr->ai_socktype, ptr->ai_protocol);
            if (Sending_socket == INVALID_SOCKET)
            {
                std::cout << "socket failed: " << WSAGetLastError() << "\n";
                freeaddrinfo(result);
                WSACleanup();
                return 0;
            }
     
            // now we connect to the server
            ret = connect(Sending_socket, ptr->ai_addr, (int)ptr->ai_addrlen);
            if (ret == 0)
                break;

            std::cout << "Error at socket(): " << WSAGetLastError() << "\n";

            closesocket(Sending_socket);
            Sending_socket = INVALID_SOCKET;
        }
    }
    */

    freeaddrinfo(result);

    if (Sending_socket != INVALID_SOCKET)
    {
        std::cout << "connect okay\n";

        // use Sending_socket as needed...

        closesocket(Sending_socket);
        ret = 1;
    }
    else
    {
        std::cout << "connect not okay\n";
        ret = 0;
    }

    // When your application is finished call WSACleanup
    WSACleanup();

    return ret;
}

Answer 2

Use getaddrinfo instead.

引用微软的inet_addr function文档

inet_addr 函数将包含IPv4 点分十进制地址 的字符串转换为IN_ADDR 结构的正确地址。

强调我的。没有点分十进制地址，没有地址。

还值得注意的是文档页面的返回值部分，

如果 cp 参数中的字符串不包含合法的 Internet 地址，例如，如果“a.b.c.d”地址的一部分超过 255，则 inet_addr 返回值 INADDR_NONE。

始终检查返回值以确保它没有给出错误消息。