Movatterモバイル変換

tzset(3p) — Linux manual page

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

PROLOG        top

       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        top

       daylight, timezone, tzname, tzset — set timezone conversion       information

SYNOPSIS        top

       #include <time.h>       extern int daylight;       extern long timezone;       extern char *tzname[2];       void tzset(void);

DESCRIPTION        top

       Thetzset() function shall use the value of the environment       variableTZ to set time conversion information used byctime(3p),localtime(3p),mktime(3p), andstrftime(3p).  IfTZ is absent from       the environment, implementation-defined default timezone       information shall be used.       Thetzset() function shall set the external variabletzname as       follows:           tzname[0] = "std";           tzname[1] = "dst";       wherestd anddst are as described in the Base Definitions volume       of POSIX.1‐2017,Chapter 8,Environment Variables.       Thetzset() function also shall set the external variabledaylight       to 0 if Daylight Savings Time conversions should never be applied       for the timezone in use; otherwise, non-zero. The external       variabletimezone shall be set to the difference, in seconds,       between Coordinated Universal Time (UTC) and local standard time.       If a thread accessestzname,daylight, ortimezone directly while       another thread is in a call totzset(), or to any function that is       required or allowed to set timezone information as if by callingtzset(), the behavior is undefined.

RETURN VALUE        top

       Thetzset() function shall not return a value.

ERRORS        top

       No errors are defined.The following sections are informative.

EXAMPLES        top

       ExampleTZ 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        top

       Since thectime(),localtime(),mktime(),strftime(), andstrftime_l() functions are required to set timezone information as       if by callingtzset(), there is no need for an explicittzset()       call before using these functions. However, portable applications       should calltzset() explicitly before usingctime_r() orlocaltime_r() because setting timezone information is optional for       those functions.

RATIONALE        top

       None.

FUTURE DIRECTIONS        top

       None.

SEE ALSO        top

ctime(3p),localtime(3p),mktime(3p),strftime(3p)       The Base Definitions volume of POSIX.1‐2017,Chapter 8,Environment Variables,time.h(0p)

COPYRIGHT        top

       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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017TZSET(3P)

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

HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH.