Using Dates

This functionality is wrapped in the Time class so there is no Date class.

Let go through the basics. There are two times in Windows, system time and local time.

System time is expressed in UTC (Coordinated Universal Time). Local time is the time for the localized system. For example right now in a workspace:

Time getSystemTime

shows: 5:42:38 PM - 3/6/2005

Time getLocalTime

shows: 10:42:38 AM - 3/6/2005

This is because I am currently at UTC - 7 hours (I am in Colorado).

UTC is used in several places in Smalltalk MT, for example the timestamp in the change log is UTC. This allows change logs to be correctly timed regardless of where and what system it was created on. Otherwise imagine if I created a method in one time zone and sent it to another time zone.

A windows date time structure (called a SYSTEMTIME) holds year, month, day of week, day, hour, seconds, milliseconds.

Time zone information can be obtained by using

Time getTimeZoneInformation

If you inspect the result you will be looking at a TIME_ZONE_INFORMATION structure.

To manipulate time, the easiest was is to first convert the SYSTEMTIME to a FILETIME. The FILETIME structure is a 64-bit value representing the number of 100-nanosecond intervals since January 1, 1601 (UTC).

This means that 10000000 (1 with 7 zeros) represents 1 second (since a nanosecond is 10^9, 100 nanoseconds is 10^7).

For example, to take the current local time and add 1 hour, you would use the following (1 hour is = 1 hour * 60 minutes * 60 seconds * 10000000).

initialTime := Time getLocalTime.
fileTime := initialTime asFileTime.
fileTime := fileTime + (1*60*60*10000000).
newTime := Time fromFileTime: fileTime.
 

Inspect initialTime and newTime and they will be 1 hour apart.