TZSET
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
PROLOG
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.
NAME
daylight,
timezone,
tzname,
tzset
--- set timezone conversion information
SYNOPSIS
#include <time.h>
extern int daylight;
extern long timezone;
extern char *tzname[2];
void tzset(void);
DESCRIPTION
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[0] = "std";
tzname[1] = "dst";
where
std
and
dst
are as described in the Base Definitions volume of POSIX.1-2017,
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.
If a thread accesses
tzname,
daylight,
or
timezone
directly while another thread is in a call to
tzset(),
or to any function that is required or allowed to set timezone
information as if by calling
tzset(),
the behavior is undefined.
RETURN VALUE
The
tzset()
function shall not return a value.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
Example
TZ
variables and their timezone differences are given in the table below:
| TZ | timezone
|
|
| EST5EDT | 5*60*60
|
| GMT0 | 0*60*60
|
| JST-9 | -9*60*60
|
| MET-1MEST | -1*60*60
|
| MST7MDT | 7*60*60
|
| PST8PDT | 8*60*60
|
|
APPLICATION USAGE
Since the
ctime(),
localtime(),
mktime(),
strftime(),
and
strftime_l()
functions are required to set timezone information as if by calling
tzset(),
there is no need for an explicit
tzset()
call before using these functions. However, portable applications
should call
tzset()
explicitly before using
ctime_r()
or
localtime_r()
because setting timezone information is optional for those functions.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
ctime(),
localtime(),
mktime(),
strftime()
The Base Definitions volume of POSIX.1-2017,
Chapter 8, Environment Variables,
<time.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
Any typographical or formatting errors that appear
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