VariantTimeToSystemTime function (oleauto.h)

Article
2021-10-13

Converts the variant representation of time to system time values.

Syntax

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

Parameters

[in] vtime

The variant time to convert.

[out] lpSystemTime

Receives the system time.

Return value

The function returns TRUE on success and FALSE otherwise.

Remarks

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.

Requirements

Requirement	Value
Target Platform	Windows
Header	oleauto.h
Library	OleAut32.lib
DLL	OleAut32.dll

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