C++ 獲取當前日期精確到毫秒的幾種方法

#include <stdio.h>
#include <string.h>
#include <sys/time.h>
#include <iostream>
#include <iomanip>
#include <ctime>
#include <chrono>
/*
取當前時間，精確到微秒；
*/
int main(int argc, char *argv[])
{
    auto now = std::chrono::system_clock::now();
    //通過不同精度獲取相差的毫秒數
    uint64_t dis_millseconds = std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch()).count()
        - std::chrono::duration_cast<std::chrono::seconds>(now.time_since_epoch()).count() * 1000;
    time_t tt = std::chrono::system_clock::to_time_t(now);
    auto time_tm = localtime(&tt);
    char strTime[25] = { 0 };
    sprintf(strTime, "%d-%02d-%02d %02d:%02d:%02d %03d", time_tm->tm_year + 1900,
        time_tm->tm_mon + 1, time_tm->tm_mday, time_tm->tm_hour,
        time_tm->tm_min, time_tm->tm_sec, (int)dis_millseconds);
    std::cout << strTime << std::endl;
    return 1;
}

#include <ctime>
#include <string>
#include <chrono>
#include <sstream>
#include <iomanip>
#include <iostream>

// use strftime to format time_t into a "date time"
std::string date_time(std::time_t posix)
{
    char buf[20]; // big enough for 2015-07-08 10:06:51\0
    std::tm tp = *std::localtime(&posix);
    return {buf, std::strftime(buf, sizeof(buf), "%F %T", &tp)};
}

std::string stamp()
{
    using namespace std;
    using namespace std::chrono;

    // get absolute wall time
    auto now = system_clock::now();

    // find the number of milliseconds
    auto ms = duration_cast<milliseconds>(now.time_since_epoch()) % 1000;

    // build output string
    std::ostringstream oss;
    oss.fill('0');

    // convert absolute time to time_t seconds
    // and convert to "date time"
    oss << date_time(system_clock::to_time_t(now));
    oss << '.' << setw(3) << ms.count();

    return oss.str();
}

int main()
{
    std::cout << stamp() << '\n';
}

std::string stamp()
{
    using namespace std;
    using namespace std::chrono;

    auto now = system_clock::now();

    // use microseconds % 1000000 now
    auto us = duration_cast<microseconds>(now.time_since_epoch()) % 1000000;

    std::ostringstream oss;
    oss.fill('0');

    oss << date_time(system_clock::to_time_t(now));
    oss << '.' << setw(6) << us.count();

    return oss.str();
}