SystemTimeToFileTime

SystemTimeToFileTime is a Win32 API function that converts a time expressed as a SYSTEMTIME structure to a FILETIME structure representing the same moment in Coordinated Universal Time (UTC). FILETIME stores time as a 64-bit value counting 100-nanosecond intervals since January 1, 1601 (UTC). The conversion maps the calendar-based fields of SYSTEMTIME (year, month, day, hour, minute, second, milliseconds) to the corresponding FILETIME value, which is stored as two 32-bit parts (dwLowDateTime and dwHighDateTime).

The function has the signature BOOL SystemTimeToFileTime(const SYSTEMTIME* lpSystemTime, LPFILETIME lpFileTime). The first parameter is a pointer to a valid SYSTEMTIME in UTC; the second receives the resulting FILETIME. The function returns a nonzero value on success; if the conversion fails (for example, due to an invalid date/time or a value outside the representable range), it returns zero and GetLastError provides extended error information.

Notes and context: SystemTimeToFileTime assumes the input SYSTEMTIME is in UTC. If your time is in local time, convert it to UTC first using appropriate time-zone conversion functions, such as TzSpecificLocalTimeToSystemTime or SystemTimeToTzSpecificLocalTime. Conversely, FileTimeToSystemTime converts a FILETIME to a UTC SYSTEMTIME. Functions like GetSystemTimeAsFileTime can obtain the current UTC FILETIME directly. The API is declared in Windows.h and linked against Kernel32.lib.