Time - The Old New Thing

A question about the FileTimeToLocalFileTime function turned out to be something else

March 6, 2015 Mar 6, 2015 03/6/15

Raymond Chen

Negative time.

Converting from a UTC-based SYSTEMTIME directly to a local-time-based SYSTEMTIME

March 7, 2014 Mar 7, 2014 03/7/14

Raymond Chen

Last year, I presented this commutative diagram A 2-by-2 grid of boxes. The top row is labeled FILETIME; the bottom row is labeled SYSTEMTIME. The first column is labeled UTC; the second column is labeled Local. The upper left box is labeled GetSystemTimeAsFileTime. There is an outgoing arrow ...

On the various ways of getting the current time and date in Win32

November 1, 2013 Nov 1, 2013 11/1/13

Raymond Chen

There are a number of functions in Win32 that obtain the current date and time. Here's how they fit together: The starting point is GetSystemTimeAsFileTime. This returns the current time in UTC in the form of a FILETIME structure. This also happens to be the time format used internally by the system, so this ...

Why do Explorer and the command prompt interpret file times differently?

March 8, 2013 Mar 8, 2013 03/8/13

Raymond Chen

A customer observed that if they use Explorer to view the timestamp on a file, it is not always in agreement with the value shown if they run a plain DIR in a command prompt. They are sometimes off by an hour. Why is that? Whenever you hear the phrase "off by an hour" you should immediately think "Daylight Saving Time". The formatting of ...

How do I parse a string into a FILETIME?

November 2, 2012 Nov 2, 2012 11/2/12

Raymond Chen

Public Service Announcement: Daylight Saving Time ends in most parts of the United States this weekend. Other parts of the world may change on a different day from the United States. The NLS functions in Win32 provide functions to convert a SYSTEMTIME into a string, but it does not provide any functions to perform the reverse conversion...

To some people, time zones are just a fancy way of sounding important

March 9, 2012 Mar 9, 2012 03/9/12

Raymond Chen

Standard time sounds much more standard.

How do I generate a unique 32-bit value for a time zone?

November 4, 2011 Nov 4, 2011 11/4/11

Raymond Chen

Public Service Announcement: Daylight Saving Time ends in most parts of the United States this weekend. Other parts of the world may change on a different day from the United States. A customer asked the following question: Given two TIME_ZONE_INFORMATION structures, I would like to compute a LONG for each that I can then compare to ...

Why does my TIME_ZONE_INFORMATION have the wrong DST cutover date?

March 11, 2011 Mar 11, 2011 03/11/11

Raymond Chen

Public Service Announcement: Daylight Saving Time begins in most parts of the United States this weekend. Other parts of the world may change on a different day from the United States. A customer reported that they were getting incorrect values from the GetTimeZoneInformationForYear function. I have a program that calls ...

Why does the Win32 Time service require the date to be correct before it will set the time?

November 5, 2010 Nov 5, 2010 11/5/10

Raymond Chen

Public Service Announcement: Daylight Saving Time ends in most parts of the United States this weekend. Andy points out that if you attempt to synchronize your clock when the date is set incorrectly, the operation fails with the error message "An error occurred while Windows was synchronizing with time.windows.com. For security reasons, ...

Why does the OLE variant date format use 30 December 1899 as its zero point?

March 12, 2010 Mar 12, 2010 03/12/10

Raymond Chen

In 2006, via the suggestion box, Chris J asks why the OLE variant date format has such a strange zero point. Its zero point is 30 December 1899, as opposed to 1 January 1900 (SQL Server's zero point) or 1 January 1970 (the unix zero point). It turns out I don't have to answer this because Eric Lippert explained it three years before ...