tzset(3p) — Linux manual page

TZSET(3P)               POSIX Programmer's Manual              TZSET(3P)

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(3p),
       localtime(3p), mktime(3p), and strftime(3p).  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(3p), localtime(3p), mktime(3p), strftime(3p)

       The Base Definitions volume of POSIX.1‐2017, Chapter 8,
       Environment Variables, time.h(0p)

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 in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                         TZSET(3P)

Pages that refer to this page: time.h(0p), daylight(3p), localtime(3p), mktime(3p), strftime(3p), timezone(3p)

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