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NAME

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

SYNOPSIS

#include <time.h>



[XSI] extern int daylight;
extern long timezone;


[CX] extern char *tzname[2];
void tzset(void);

DESCRIPTION

Thetzset() function shall use the value of the environment variableTZ to set time conversion information used byctime(),localtime(),mktime(), andstrftime(). IfTZ isabsent 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 XBD8. EnvironmentVariables.

^[XSI]Thetzset() function also shall set the external variabledaylight to 0 if Daylight Saving Time conversions shouldnever be applied for the timezone in use; otherwise, non-zero. The external variabletimezone shall be set to thedifference, in seconds, between Coordinated Universal Time (UTC) and local standard time.

If a thread accessestzname,^[XSI]daylight, ortimezone  directly while another thread is in a call totzset(), or to any function that isrequired or allowed to set timezone information as if by callingtzset(), the behavior is undefined.

RETURN VALUE

Thetzset() function shall not return a value.

ERRORS

No errors are defined.

EXAMPLES

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

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 applicationsshould calltzset() explicitly before usinglocaltime_r() because settingtimezone information is optional for that function.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

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

XBD8. Environment Variables,<time.h>

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 6

The example is corrected.

Issue 7

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0377 [880] is applied.

Issue 8

Austin Group Defect 1253 is applied, changing "Daylight Savings" to "Daylight Saving".

Austin Group Defect 1410 is applied, removing thectime_r() function.