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.1‐2008, 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.

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

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       ctime(), localtime(), mktime(), strftime()

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables, <time.h>

COPYRIGHT

       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 .

       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 .