test.h

#pragma once
#include <winsock2.h>
#include <ws2tcpip.h>
#include<ctime>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#pragma   comment   (lib,"Ws2_32.lib")
struct NTPPacket
{
    union
    {
        struct _ControlWord
        {
            unsigned int uLI : 2;       // 00 = no leap, clock ok   
            unsigned int uVersion : 3;  // version 3 or version 4
            unsigned int uMode : 3;     // 3 for client, 4 for server, etc.
            unsigned int uStratum : 8;  // 0 is unspecified, 1 for primary reference system,
                                        // 2 for next level, etc.
            int nPoll : 8;              // seconds as the nearest power of 2
            int nPrecision : 8;         // seconds to the nearest power of 2
        };

        int nControlWord;             // 4
    };

    int nRootDelay;                   // 4
    int nRootDispersion;              // 4
    int nReferenceIdentifier;         // 4

    __int64 n64ReferenceTimestamp;    // 8
    __int64 n64OriginateTimestamp;    // 8
    __int64 n64ReceiveTimestamp;      // 8

    int nTransmitTimestampSeconds;    // 4
    int nTransmitTimestampFractions;  // 4
};

.cpp

#include <iostream>
#include <string>
#include <atlstr.h>
#include <vector>
#include <io.h>
#include <stdlib.h>
#include <iostream>
#pragma warning(disable:4996) 

#define JAN_1970 0x83aa7e80 /* 1900年～1970年之间的时间秒数 */

using namespace std;
#include"test.h"//包含上面的头文件，文件名自取

int Get_time_t(time_t & ttime)
{
    ttime = 0;
    WSADATA wsaData;
    // Initialize Winsock
    int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) return 1;
    int result, count;
    int sockfd = 0, rc;
    sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (sockfd < 0) return 2;
    fd_set pending_data;
    timeval block_time;
    NTPPacket ntpSend = { 0 };
    ntpSend.nControlWord = 0x1B;
    NTPPacket ntpRecv;
    SOCKADDR_IN addr_server;
    addr_server.sin_family = AF_INET;
    addr_server.sin_port = htons(123);//NTP服务默认为123端口号
    addr_server.sin_addr.S_un.S_addr = inet_addr("120.25.115.20"); //该地址为阿里云NTP服务器的公网地址，其他NTP服务器地址可自行百度搜索。
    SOCKADDR_IN sock;
    int len = sizeof(sock);

    if ((result = sendto(sockfd, (const char*)&ntpSend, sizeof(NTPPacket), 0, (SOCKADDR *)&addr_server, sizeof(SOCKADDR))) < 0)
    {
        int err = WSAGetLastError();
        return 3;
    }
    FD_ZERO(&pending_data);
    FD_SET(sockfd, &pending_data);
    //timeout 10 sec
    block_time.tv_sec = 10;
    block_time.tv_usec = 0;
    if (select(sockfd + 1, &pending_data, NULL, NULL, &block_time) > 0)
    {
        //获取的时间为1900年1月1日到现在的秒数
        if ((count = recvfrom(sockfd, (char*)&ntpRecv, sizeof(NTPPacket), 0, (SOCKADDR*)&sock, &len)) > 0)
            ttime = ntohl(ntpRecv.nTransmitTimestampSeconds) - JAN_1970;
    }
    closesocket(sockfd);
    WSACleanup();
    return 0;
}
int main() {
    //获取到的t为一个时间戳，请根据需求转换成可视化时间
    time_t  rawtime;
    int filecode = Get_time_t(rawtime);
    if (filecode == 0)
    {
        char cTimePARTNUMBER[256] = "";
        struct tm * timeinfo;
        //time(&rawtime);
        timeinfo = localtime(&rawtime);
        char buffer1[256];
        strftime(cTimePARTNUMBER, sizeof(buffer1), "%Y%m%d-%H:%M:%S", timeinfo);
        string strTimePARTNUMBER = "";
        strTimePARTNUMBER = cTimePARTNUMBER;
        cout << strTimePARTNUMBER << endl;
    }
    else
    {
        cout << filecode << endl;
    }
    cin.get();
    return 0;
}