Windows C++ 获取网络时间

可以使用Winsock库中的函数获取网络时间。具体步骤如下：

1. 加载Winsock库，使用WSAStartup函数初始化Winsock；
2. 使用gethostbyname函数获取一个互联网主机的IP地址；
3. 使用SOCKET函数创建一个套接字；
4. 使用connect函数连接到指定主机；
5. 向指定主机发送一条NTP协议的请求报文，可以参考RFC 5905；
6. 接收并解析指定主机返回的NTP协议的应答报文；
7. 计算出网络时间。

以下是一个简单的示例代码：

#include <winsock2.h>
#include <ws2tcpip.h>
#include <time.h>

#pragma comment(lib, "ws2_32.lib")

#define NTP_TIMESTAMP_DELTA 2208988800ull

int main()
{
    // 初始化Winsock
    WSADATA wsaData;
    int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed with error: %d\n", iResult);
        return 1;
    }

    // 获取IP地址
    struct addrinfo* result = NULL;
    struct addrinfo hints;
    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_DGRAM;
    hints.ai_protocol = IPPROTO_UDP;
    iResult = getaddrinfo("pool.ntp.org", "123", &hints, &result);
    if (iResult != 0) {
        printf("getaddrinfo failed: %d\n", iResult);
        WSACleanup();
        return 1;
    }

    // 创建套接字
    SOCKET socketNTP = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (socketNTP == INVALID_SOCKET) {
        printf("socket failed with error: %ld\n", WSAGetLastError());
        freeaddrinfo(result);
        WSACleanup();
        return 1;
    }

    // 连接到指定主机
    iResult = connect(socketNTP, result->ai_addr, (int)result->ai_addrlen);
    if (iResult == SOCKET_ERROR) {
        printf("connect failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(socketNTP);
        WSACleanup();
        return 1;
    }

    // 发送NTP请求报文
    char ntpPacket[48] = {0x1b};
    iResult = send(socketNTP, ntpPacket, sizeof(ntpPacket), 0);
    if (iResult == SOCKET_ERROR) {
        printf("send failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(socketNTP);
        WSACleanup();
        return 1;
    }

    // 接收NTP应答报文
    char ntpResponse[48];
    iResult = recv(socketNTP, ntpResponse, sizeof(ntpResponse), 0);
    if (iResult == SOCKET_ERROR) {
        printf("recv failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(socketNTP);
        WSACleanup();
        return 1;
    }

    // 解析NTP应答报文
    unsigned long long ntpTimestamp = ((unsigned long long)ntpResponse[40] << 24) |
                                      ((unsigned long long)ntpResponse[41] << 16) |
                                      ((unsigned long long)ntpResponse[42] << 8) |
                                      ((unsigned long long)ntpResponse[43]);
    ntpTimestamp -= NTP_TIMESTAMP_DELTA;
    time_t networkTime = (time_t)ntpTimestamp;

    // 输出网络时间
    printf("Network Time: %s", ctime(&networkTime));

    freeaddrinfo(result);
    closesocket(socketNTP);
    WSACleanup();

    return 0;
}

注意：以上代码仅作为示例，实际使用时需要进行错误处理和异常情况的处理。