cpp get current time's precision to milliseconds,such as yyyymmddHHMMSSfff

//model/util.h
#pragma once
#ifndef __util_h__
#define __util_h__
#include <chrono>
#include <ctime>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <sstream>
#include <string>
#include <thread>
#include <unistd.h>
#include <vector>

using namespace std;

class util
{
public:
    void time_demo();
    void print_time();
};
#endif


//model/util.cpp
#include "model/util.h"

void util::time_demo()
{    
    chrono::time_point<chrono::high_resolution_clock> now = chrono::high_resolution_clock::now();
    cout<<"nanos "<<chrono::duration_cast<chrono::nanoseconds>(now.time_since_epoch()).count()
    <<",micros "<<chrono::duration_cast<chrono::microseconds>(now.time_since_epoch()).count()
    <<",mills "<<chrono::duration_cast<chrono::milliseconds>(now.time_since_epoch()).count()
    <<",seconds "<<chrono::duration_cast<chrono::seconds>(now.time_since_epoch()).count()<<endl; 
    chrono::milliseconds mills=chrono::duration_cast<chrono::milliseconds>(now.time_since_epoch());
    chrono::seconds seconds=chrono::duration_cast<chrono::seconds>(now.time_since_epoch());
    uint64_t millsValue=mills.count()-seconds.count()*1000;
    time_t rawTime = chrono::high_resolution_clock::to_time_t(now);
    struct tm tmInfo = *std::localtime(&rawTime);
    stringstream ss;
    ss << std::put_time(&tmInfo, "%Y%m%d%H%M%S") << std::setfill('0') << std::setw(3) << millsValue;
    string dtValue = ss.str();
    ss = stringstream(std::string());
    cout << "now is " << dtValue << endl<<endl;
}

void util::print_time()
{   
    while (1)
    {
        time_demo();
        usleep(100000);
    } 
}

//main.cpp

#include "model/util.h"

void print_time_demo()
{
    util ul;
    ul.print_time();
}

int main(int args,char **argv)
{
    print_time_demo();
}

Compile

g++ -g -std=c++2a -I. *.cpp ./model/*.cpp -o h1 -luuid -lpthread

Run