Starting from March 2007, the Daylight Savings Time (DST) start date and end date for the United States will change. DST will start at 2:00 A.M. on the second Sunday in March and end at 2:00 A.M on the first Sunday in November.

The C Run-Time (CRT) performs its own time handling only when the TZ environment variable is set, or when an underlying OS API time call fails.  If the TZ environment variably is not set, the CRT calls the Windows APIs and exhibits Windows behavior. Windows Updates are available which allow Windows to correctly calculate time based on the new DST rules. CRT Updates are available for the CRTs which ship with every currently supported version of Visual Studio and  CRT updates are also available for the CRT which ships with Windows to continue to correctly handle DST conversions in U.S. time zones based on the new DST rules.

Get more information on Preparing for Daylight Saving Time changes in 2007

Get more information on How to handle dates and times that include DST

Thanks,

Sarita Bafna – Visual C++ Team