This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding Linux
manual page for details of Linux behavior), or the interface may not be
implemented on Linux.
daylight, timezone, tzname, tzset — set timezone conversion information
extern int daylight;
extern long timezone;
extern char *tzname;
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 follows:
tzname = "std";
tzname = "dst";
where std and dst are as described in the Base
Definitions volume of POSIX.1‐2008, Chapter 8, Environment
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.
The tzset() function shall not return a value.
No errors are defined.
The following sections are informative.
Example TZ variables and their timezone differences are given in the
ctime(), localtime(), mktime(),
The Base Definitions volume of POSIX.1‐2008, Chapter
8, Environment Variables, <time.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
7, Copyright (C) 2013 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013
Technical Corrigendum 1 applied.) 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.unix.org/online.html .
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