c++ - 将 FILETIME 转换为可移植时间单位

Question

我将如何转换 Windows FILETIME将对象转换为 time_t 或原始秒/毫秒？我正在将一些代码从 Windows 移植到 Unix，因此我不能依赖 Windows API 函数。

Answer 1

FILETIME 定义为

Contains a 64-bit value representing the number of 100-nanosecond intervals since January 1, 1601 (UTC).

因此，要将其转换为 Unix 时间，只需减去两个纪元时间并将 100 纳秒间隔转换为秒/毫秒即可。任何数量的工具/站点都会告诉您这两个纪元相隔 134774 天(或 11644473600 秒)。因此:

void convert_filetime(struct timeval *out_tv, const FILETIME *filetime)
{
    // Microseconds between 1601-01-01 00:00:00 UTC and 1970-01-01 00:00:00 UTC
    static const uint64_t EPOCH_DIFFERENCE_MICROS = 11644473600000000ull;

    // First convert 100-ns intervals to microseconds, then adjust for the
    // epoch difference
    uint64_t total_us = (((uint64_t)filetime->dwHighDateTime << 32) | (uint64_t)filetime->dwLowDateTime) / 10;
    total_us -= EPOCH_DIFFERENCE_MICROS;

    // Convert to (seconds, microseconds)
    out_tv->tv_sec = (time_t)(total_us / 1000000);
    out_tv->tv_usec = (useconds_t)(total_us % 1000000);
}