The question naturally arises, how does the library determine this local time?
The UNIX operating system provides for setting the local time zone and for establishing whether DST is locally observed. Class RWTime uses various system calls to determine these values and sets itself accordingly. Class RWTime should function properly in North America or places where DST is not observed. In places not governed by United States DST rules, you may need to re-initialize the local time zone_see RWZone in the Class Reference.
Users of the various Windows operating systems may have to set the time switches manually. How you do this depends on your compiler. If you do nothing, the class will function properly for local time, but may not give the proper GMT because the computer has no way of knowing the offset from local time to GMT.
If you use Borland, MetaWare, Microsoft, Symantec, or Watcom, you must set your environment variable TZ to the appropriate time zone. For example:
set TZ=PST8PDT
For further information, see the documentation for function tzset()or _tzset() in your compiler's run-time library reference.
Finally, it is essential that your computer's system clock be set and functioning correctly. If you are using a PC, be sure the batteries that power the system clock are charged.