Converts a system time to a variant representation.
A variant time is stored as an 8-byte real value (double), representing a date between January 1, 100 and December 31, 9999, inclusive. The value 2.0 represents January 1, 1900; 3.0 represents January 2, 1900, and so on. Adding 1 to the value increments the date by a day. The fractional part of the value represents the time of day. Therefore, 2.5 represents noon on January 1, 1900; 3.25 represents 6:00 A.M. on January 2, 1900, and so on. Negative numbers represent dates prior to December 30, 1899.
The variant time resolves to one second. Any milliseconds in the input date are ignored.
The LPSYSTEMTIME structure is useful for the following reasons:
It spans all time/date periods. MS-DOS date/time is limited to representing only those dates between 1/1/1980 and 12/31/2107.
The date/time elements are all easily accessible without needing to do any bit decoding.
The National Data Support data and time formatting functions GetDateFormat and GetTimeFormat take a LPSYSTEMTIME value as input. For more information, see the COM Programmers Reference in the Platform SDK.
It is the default Win32 time/date data format supported by Windows NT and Windows 95.
The SystemTimeToVariantTime function will accept invalid dates and try to fix them when resolving to a VARIANT time. For example, an invalid date such as 2/29/2001 will resolve to 3/1/2001. Only days are fixed, so invalid month values result in an error being returned. Days are checked to be between 1 and 31. Negative days and days greater than 31 results in an error. A day less than 31 but greater than the maximum day in that month has the day promoted to the appropriate day of the next month. A day equal to zero resolves as the last day of the previous month. For example, an invalid dates such as 2/0/2001 will resolve to 1/31/2001.