VariantTimeToSystemTime function (oleauto.h)

Converts the variant representation of time to system time values.

INT VariantTimeToSystemTime(
  [in]  DOUBLE       vtime,
  [out] LPSYSTEMTIME lpSystemTime
);

[in] vtime

The variant time to convert.

[out] lpSystemTime

Receives the system time.

The function returns TRUE on success and FALSE otherwise.

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 the dates prior to December 30, 1899.

Using the SYSTEMTIME structure is useful because:

• 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 Language Support data and time formatting functions GetDateFormat and GetTimeFormat take a SYSTEMTIME value as input.
• It is the default Win32 time and date data format supported by Windows NT and Windows 95.

The VariantTimeToSystemTime 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.