инициализировать информацию о преобразовании времени (initialize time conversion information)
Имя (Name)
tzset, tzname, timezone, daylight - initialize time conversion
information
Синопсис (Synopsis)
#include <time.h>
void tzset(void);
extern char *tzname[2];
extern long timezone;
extern int daylight;
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
tzset():
_POSIX_C_SOURCE
tzname:
_POSIX_C_SOURCE
timezone, daylight:
_XOPEN_SOURCE
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _SVID_SOURCE
Описание (Description)
The tzset() function initializes the tzname variable from the TZ
environment variable. This function is automatically called by
the other time conversion functions that depend on the timezone.
In a System-V-like environment, it will also set the variables
timezone (seconds West of UTC) and daylight (to 0 if this
timezone does not have any daylight saving time rules, or to
nonzero if there is a time, past, present, or future when
daylight saving time applies).
If the TZ variable does not appear in the environment, the system
timezone is used. The system timezone is configured by copying,
or linking, a file in the tzfile(5) format to /etc/localtime. A
timezone database of these files may be located in the system
timezone directory (see the FILES section below).
If the TZ variable does appear in the environment, but its value
is empty, or its value cannot be interpreted using any of the
formats specified below, then Coordinated Universal Time (UTC) is
used.
The value of TZ can be one of two formats. The first format is a
string of characters that directly represent the timezone to be
used:
std offset[dst[offset][,start[/time],end[/time]]]
There are no spaces in the specification. The std string
specifies an abbreviation for the timezone and must be three or
more alphabetic characters. When enclosed between the less-than
(<) and greater-than (>) signs, the characters set is expanded to
include the plus (+) sign, the minus (-) sign, and digits. The
offset string immediately follows std and specifies the time
value to be added to the local time to get Coordinated Universal
Time (UTC). The offset is positive if the local timezone is west
of the Prime Meridian and negative if it is east. The hour must
be between 0 and 24, and the minutes and seconds 00 and 59:
[+|-]hh[:mm[:ss]]
The dst string and offset specify the name and offset for the
corresponding daylight saving timezone. If the offset is
omitted, it defaults to one hour ahead of standard time.
The start field specifies when daylight saving time goes into
effect and the end field specifies when the change is made back
to standard time. These fields may have the following formats:
Jn This specifies the Julian day with n between 1 and 365.
Leap days are not counted. In this format, February 29
can't be represented; February 28 is day 59, and March 1
is always day 60.
n This specifies the zero-based Julian day with n between 0
and 365. February 29 is counted in leap years.
Mm.w.d This specifies day d (0 <= d <= 6) of week w (1 <= w <= 5)
of month m (1 <= m <= 12). Week 1 is the first week in
which day d occurs and week 5 is the last week in which
day d occurs. Day 0 is a Sunday.
The time fields specify when, in the local time currently in
effect, the change to the other time occurs. If omitted, the
default is 02:00:00.
Here is an example for New Zealand, where the standard time
(NZST) is 12 hours ahead of UTC, and daylight saving time (NZDT),
13 hours ahead of UTC, runs from the first Sunday in October to
the third Sunday in March, and the changeovers happen at the
default time of 02:00:00:
TZ="NZST-12:00:00NZDT-13:00:00,M10.1.0,M3.3.0"
The second format specifies that the timezone information should
be read from a file:
:[filespec]
If the file specification filespec is omitted, or its value
cannot be interpreted, then Coordinated Universal Time (UTC) is
used. If filespec is given, it specifies another
tzfile(5)-format file to read the timezone information from. If
filespec does not begin with a '/', the file specification is
relative to the system timezone directory. If the colon is
omitted each of the above TZ formats will be tried.
Here's an example, once more for New Zealand:
TZ=":Pacific/Auckland"
Окружение (Environment)
TZ If this variable is set its value takes precedence over
the system configured timezone.
TZDIR If this variable is set its value takes precedence over
the system configured timezone database directory path.
Файлы (Files)
/etc/localtime
The system timezone file.
/usr/share/zoneinfo/
The system timezone database directory.
/usr/share/zoneinfo/posixrules
When a TZ string includes a dst timezone without anything
following it, then this file is used for the start/end
rules. It is in the tzfile(5) format. By default, the
zoneinfo Makefile hard links it to the America/New_York
tzfile.
Above are the current standard file locations, but they are
configurable when glibc is compiled.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────────┬───────────────┬────────────────────┐
│Interface │ Attribute │ Value │
├───────────────────────────┼───────────────┼────────────────────┤
│tzset() │ Thread safety │ MT-Safe env locale │
└───────────────────────────┴───────────────┴────────────────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
Примечание (Note)
4.3BSD had a function char *timezone(zone, dst) that returned the
name of the timezone corresponding to its first argument (minutes
West of UTC). If the second argument was 0, the standard name
was used, otherwise the daylight saving time version.
Смотри также (See also)
date(1), gettimeofday(2), time(2), ctime(3), getenv(3), tzfile(5)
