WIN32 : Date/Time conversion and strftime

DateTimeConversionAndStrfTime.cpp

#include <windows.h>
#include <time.h>
#include <stdio.h>
#include <stdint.h>

// http://www.programmingforums.org/post45492.html
static const int64_t EPOCH_DIFF =  0x019DB1DED53E8000LL; // 116444736000000000 nsecs
static const int RATE_DIFF = 10000000; // 100 nsecs

time_t tmToUnixTime(const struct tm& stm) {
    auto tm = stm;
    return mktime(&tm);
}

struct tm unixTimeToTm(time_t unixTime) {
    struct tm stm {};
    gmtime_s(&stm, &unixTime);
    return stm;
}

FILETIME unixTimeToWin32FileTime(time_t unixTime) {
    auto t = (static_cast<int64_t>(unixTime) * RATE_DIFF) + EPOCH_DIFF;
    return * reinterpret_cast<const FILETIME*>(&t);
}

time_t win32FileTimeToUnixTime(const FILETIME& win32FileTime) {
    const auto ft = * reinterpret_cast<const int64_t*>(&win32FileTime);
    auto t = (ft - EPOCH_DIFF) / RATE_DIFF;
    return static_cast<time_t>(t);
}

SYSTEMTIME win32FileTimeToSystemTime(const FILETIME& win32FileTime) {
    SYSTEMTIME st;
    FileTimeToSystemTime(&win32FileTime, &st);
    return st;
}

FILETIME win32SystemTimeToFileTime(const SYSTEMTIME& win32SystemTime) {
    FILETIME ft;
    SystemTimeToFileTime(&win32SystemTime, &ft);
    return ft;
}

SYSTEMTIME win32SystemTimeToLocalTime(const SYSTEMTIME& win32SystemTime) {
    SYSTEMTIME lt;
    SystemTimeToTzSpecificLocalTime(nullptr, &win32SystemTime, &lt);
    return lt;
}

SYSTEMTIME win32LocalTimeToSystemTime(const SYSTEMTIME& win32LocalTime) {
    SYSTEMTIME st;
    TzSpecificLocalTimeToSystemTime(nullptr, &win32LocalTime, &st);
    return st;
}

SYSTEMTIME win32FileTimeToLocalTime(const FILETIME& win32FileTime) {
    return win32SystemTimeToLocalTime(win32FileTimeToSystemTime(win32FileTime));
}

FILETIME win32LocalTimeToFileTime(const SYSTEMTIME& win32LocalTime) {
    return win32SystemTimeToFileTime(win32LocalTimeToSystemTime(win32LocalTime));
}

SYSTEMTIME getSystemTime() {
    SYSTEMTIME st;
    GetSystemTime(&st);
    return st;
}

SYSTEMTIME getLocalTime() {
    SYSTEMTIME st;
    GetLocalTime(&st);
    return st;
}



int main() {
    const auto lt = getLocalTime();
    const auto ft = win32LocalTimeToFileTime(lt);
    const auto ut = win32FileTimeToUnixTime(ft);
    const auto tm = unixTimeToTm(ut);

    static const char* fmts[][2] = {
        { "%a", "Abbreviated weekday name" },
        { "%A", "Full weekday name" },
        { "%b", "Abbreviated month name" },
        { "%B", "Full month name" },
        { "%c", "Date and time representation appropriate for locale" },
        { "%d", "Day of month as decimal number (01..31)" },
        { "%H", "Hour in 24-hour format (00..23)" },
        { "%I", "Hour in 12-hour format (01..12)" },
        { "%j", "Day of year as decimal number (001..366)" },
        { "%m", "Month as decimal number (01..12)" },
        { "%M", "Minute as decimal number (00..59)" },
        { "%p", "Current locale's A.M./P.M. indicator for 12-hour clock" },
        { "%S", "Second as decimal number (00..59)" },
        { "%U", "Week of year as decimal number, with Sunday as first day of week (00..53)" },
        { "%w", "Weekday as decimal number (0..6; Sunday is 0)" },
        { "%W", "Week of year as decimal number, with Monday as first day of week (00..53)" },
        { "%x", "Date representation for current locale" },
        { "%X", "Time representation for current locale" },
        { "%y", "Year without century, as decimal number (00..99)" },
        { "%Y", "Year with century, as decimal number" },
        { "%z", "Either the time-zone name or time zone abbreviation, depending on registry settings; no characters if time zone is unknown" },
        { "%Z", "Either the time-zone name or time zone abbreviation, depending on registry settings; no characters if time zone is unknown" },
        { "%%", "Percent sign" },
    };

    for(auto& f : fmts) {
        const auto* fmt  = f[0];
        const auto* desc = f[1];
        char buf[256];
        strftime(buf, sizeof(buf), fmt, &tm);
        printf("%s -> [%-17s] : %s\n", fmt, buf, desc);
    }
}