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
The tzset () function shall use the value
of the environment variable TZ to set time conversion
information used by ctime(3),
localtime(3), mktime(3), and
strftime(3). 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 XBD V1_chap08(7).
[XSI] The tzset ()
function also shall set the external variable daylight to
0 if Daylight Saving 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,
[XSI] 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.
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(3),
localtime(3), mktime(3),
strftime(3), and strftime_l(3) 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 localtime_r(3) because setting
timezone information is optional for that function.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
ctime(3), localtime(3), mktime(3), strftime(3)
XBD V1_chap08(7), <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 the ctime_r () function.