c++ - 将从 "midnight 1904-1-1"开始的秒数转换为日期时间字符串

Question

在某些多媒体元数据中，可能存在以秒为单位的日期时间UTC 时间 1904 年 1 月 1 日午夜。

据我所知，C/C++ 标准库中的日期时间函数通常基于 1970-1-1 午夜，至少在 Visual C++ 中，C/C++/Win32-API 中是否有函数来转换秒从“1904-1-1午夜”开始到日期时间字符串，例如“hh:mm:ss MM.dd, yyyy”或其他格式字符串或类似“struct tm”的结构？

struct tm
{
    int tm_sec;   // seconds after the minute - [0, 60] including leap second
    int tm_min;   // minutes after the hour - [0, 59]
    int tm_hour;  // hours since midnight - [0, 23]
    int tm_mday;  // day of the month - [1, 31]
    int tm_mon;   // months since January - [0, 11]
    int tm_year;  // years since 1900
    int tm_wday;  // days since Sunday - [0, 6]
    int tm_yday;  // days since January 1 - [0, 365]
    int tm_isdst; // daylight savings time flag
};

解决方案#1:

int main()
{
    SYSTEMTIME systm;
    memset(&systm, 0, sizeof(systm));

    systm.wYear = 1904;
    systm.wMonth = 1;
    systm.wDay = 1;

    FILETIME filetm;
    if (SystemTimeToFileTime(&systm, &filetm) == FALSE){
        printf("Failed to convert system time to file-time.\n");
        return 0;
    }

    ULARGE_INTEGER nanoSeconds;
    nanoSeconds.HighPart = filetm.dwHighDateTime;
    nanoSeconds.LowPart = filetm.dwLowDateTime;

    nanoSeconds.QuadPart += 3600ULL * 10000000; // add 1hour based on 1904/1/1 midnight

    filetm.dwHighDateTime = nanoSeconds.HighPart;
    filetm.dwLowDateTime = nanoSeconds.LowPart;

    if (FileTimeToSystemTime(&filetm, &systm) == FALSE){
        printf("Failed to convert file-time to system time.\n");
        return 0;
    }

    printf("New system time by adding 1 hour: %d-%02d-%02d %02d:%02d:%02d.%03d\n", 
        systm.wYear, systm.wMonth, systm.wDay, 
        systm.wHour, systm.wMinute, systm.wSecond, systm.wMilliseconds);

    return 0;
}

输出为

New system time by adding 1 hour: 1904-01-01 01:00:00.000

解决方案#2:

用@Howard Hinnant的date.h也可以解决这个问题，请看他提供的示例代码https://stackoverflow.com/a/49733937/3968307

Answer 1

这是使用 Howard Hinnant's free, open-source date/time library 的好时机:

#include "date/date.h"
#include <cstdint>
#include <iostream>
#include <string>

std::string
convert(std::int64_t seconds_since_1904)
{
    using namespace date;
    using namespace std::chrono;
    constexpr auto offset = sys_days{January/1/1970} - sys_days{January/1/1904};
    return format("%T %m.%d, %Y", sys_seconds{seconds{seconds_since_1904}} - offset);
}

int
main()
{
    std::cout << convert(3'606'124'378) << '\n';
}

输出:

13:12:58 04.09, 2018

更新

以上代码将通过以下方式移植到 C++20(发布时):

• 更改#include "date/date.h"至#include <chrono>
• 更改using namespace date;至using namespace std;
• 更改"%T %m.%d, %Y"至"{:%T %m.%d, %Y}"