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 .