The tzset() function shall use the value of the environment variable
TZ to set time conversion information used by ctime() ,
localtime() , mktime() , and strftime() . If TZ is
absent from the environment, implementation-defined default timezone
information shall be used.
The tzset() function shall set the external variable tzname as
tzname = "std";tzname = "dst";
where std and dst are as described in the Base Definitions volume
of IEEE Std 1003.1-2001, Chapter 8, Environment Variables.
The tzset() function also shall set the external variable daylight
to 0 if Daylight Savings Time conversions should never be applied for the
timezone in use; otherwise, non-zero. The external variable timezone
shall be set to the difference, in seconds, between Coordinated Universal Time
(UTC) and local standard time.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html