SYSTEMTIME structure (minwinbase.h)

Specifies a date and time, using individual members for the month, day, year, weekday, hour, minute, second, and millisecond. The time is either in coordinated universal time (UTC) or local time, depending on the function that is being called.

typedef struct _SYSTEMTIME {
  WORD wYear;
  WORD wMonth;
  WORD wDayOfWeek;
  WORD wDay;
  WORD wHour;
  WORD wMinute;
  WORD wSecond;
  WORD wMilliseconds;
} SYSTEMTIME, *PSYSTEMTIME, *LPSYSTEMTIME;

wYear

The year. The valid values for this member are 1601 through 30827.

wMonth

The month. This member can be one of the following values.

wDayOfWeek

The day of the week. This member can be one of the following values.

wDay

The day of the month. The valid values for this member are 1 through 31.

wHour

The hour. The valid values for this member are 0 through 23.

wMinute

The minute. The valid values for this member are 0 through 59.

wSecond

The second. The valid values for this member are 0 through 59.

wMilliseconds

The millisecond. The valid values for this member are 0 through 999.

It is not recommended that you add and subtract values from the SYSTEMTIME structure to obtain relative times. Instead, you should

• Convert the SYSTEMTIME structure to a FILETIME structure.
• Copy the resulting FILETIME structure to a ULARGE_INTEGER structure.
• Use normal 64-bit arithmetic on the ULARGE_INTEGER value.

The system can periodically refresh the time by synchronizing with a time source. Because the system time can be adjusted either forward or backward, do not compare system time readings to determine elapsed time. Instead, use one of the methods described in Windows Time.

The following example demonstrates the difference between the time values retrieved by the GetSystemTime and GetLocalTime functions.

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

void main()
{
    SYSTEMTIME st, lt;
    
    GetSystemTime(&st);
    GetLocalTime(&lt);
    
    printf("The system time is: %02d:%02d\n", st.wHour, st.wMinute);
    printf(" The local time is: %02d:%02d\n", lt.wHour, lt.wMinute);
}

// Sample output

The system time is: 19:34
 The local time is: 12:34

FILETIME

FileTimeToSystemTime

GetLocalTime

GetSystemTime

SetLocalTime

SetSystemTime

SystemTimeToFileTime

ULARGE_INTEGER