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I needed time zone adjustment information for a current project, so decided to write a separate program to explore what is available.  Since we identify our time zone to  Windows at installation time and since it politely asks us to confirm when when it changes the clock for daylight savings time, it seems logical that the information would be available.  Sure enough Windows API function GetTimeZoneInformation returns a record, TTimeZoneInformation,  with everything you would want to know; Specifically:

• Bias - the offset in minutes to add to local time  to get UTC (Universal Time Coordinated, also/formerly known as GMT, Greenwich Mean Time).  
• Time zone name
• Daylight savings name
• Date and time for start of Daylight savings time
• Date and time for end of Daylight savings time
• Daylight savings time adjustment amount

The function also returns an integer result indicating:

• Information not available
• We are in daylight savings time
• We are not in daylight savings time

Delphi provides both the hook to the function and the record definition.  Here is a simple program that just calls GetTimeZoneInformation  and displays the results.

Download source

Download executable

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