Description
GTimeZone is a structure that represents a time zone, at no
particular point in time. It is refcounted and immutable.
Each time zone has an identifier (for example, ‘Europe/London’) which is
platform dependent. See g_time_zone_new() for information on the identifier
formats. The identifier of a time zone can be retrieved using
g_time_zone_get_identifier().
A time zone contains a number of intervals. Each interval has
an abbreviation to describe it (for example, ‘PDT’), an offet to UTC and a
flag indicating if the daylight savings time is in effect during that
interval. A time zone always has at least one interval — interval 0. Note
that interval abbreviations are not the same as time zone identifiers
(apart from ‘UTC’), and cannot be passed to g_time_zone_new().
Every UTC time is contained within exactly one interval, but a given
local time may be contained within zero, one or two intervals (due to
incontinuities associated with daylight savings time).
An interval may refer to a specific period of time (eg: the duration
of daylight savings time during 2010) or it may refer to many periods
of time that share the same properties (eg: all periods of daylight
savings time). It is also possible (usually for political reasons)
that some properties (like the abbreviation) change between intervals
without other properties changing.
GTimeZone is available since GLib 2.26.
Functions
g_time_zone_unref ()
void
g_time_zone_unref (GTimeZone *tz);
Decreases the reference count on tz
.
Since: 2.26
g_time_zone_ref ()
GTimeZone *
g_time_zone_ref (GTimeZone *tz);
Increases the reference count on tz
.
Returns
a new reference to tz
.
Since: 2.26
g_time_zone_new ()
GTimeZone *
g_time_zone_new (const gchar *identifier);
Creates a GTimeZone corresponding to identifier
.
identifier
can either be an RFC3339/ISO 8601 time offset or
something that would pass as a valid value for the TZ environment
variable (including NULL).
In Windows, identifier
can also be the unlocalized name of a time
zone for standard time, for example "Pacific Standard Time".
Valid RFC3339 time offsets are "Z" (for UTC) or
"±hh:mm". ISO 8601 additionally specifies
"±hhmm" and "±hh". Offsets are
time values to be added to Coordinated Universal Time (UTC) to get
the local time.
In UNIX, the TZ environment variable typically corresponds
to the name of a file in the zoneinfo database, an absolute path to a file
somewhere else, or a string in
"std offset [dst [offset],start[/time],end[/time]]" (POSIX) format.
There are no spaces in the specification. The name of standard
and daylight savings time zone must be three or more alphabetic
characters. Offsets are time values to be added to local time to
get Coordinated Universal Time (UTC) and should be
"[±]hh[[:]mm[:ss]]". Dates are either
"Jn" (Julian day with n between 1 and 365, leap
years not counted), "n" (zero-based Julian day
with n between 0 and 365) or "Mm.w.d" (day d
(0 <= d <= 6) of week w (1 <= w <= 5) of month m (1 <= m <= 12), day
0 is a Sunday). Times are in local wall clock time, the default is
02:00:00.
In Windows, the "tzn[+|–]hh[:mm[:ss]][dzn]" format is used, but also
accepts POSIX format. The Windows format uses US rules for all time
zones; daylight savings time is 60 minutes behind the standard time
with date and time of change taken from Pacific Standard Time.
Offsets are time values to be added to the local time to get
Coordinated Universal Time (UTC).
g_time_zone_new_local() calls this function with the value of the
TZ environment variable. This function itself is independent of
the value of TZ, but if identifier
is NULL then /etc/localtime
will be consulted to discover the correct time zone on UNIX and the
registry will be consulted or GetTimeZoneInformation() will be used
to get the local time zone on Windows.
If intervals are not available, only time zone rules from TZ
environment variable or other means, then they will be computed
from year 1900 to 2037. If the maximum year for the rules is
available and it is greater than 2037, then it will followed
instead.
See
RFC3339 §5.6
for a precise definition of valid RFC3339 time offsets
(the time-offset expansion) and ISO 8601 for the
full list of valid time offsets. See
The GNU C Library manual
for an explanation of the possible
values of the TZ environment variable. See
Microsoft Time Zone Index Values
for the list of time zones on Windows.
You should release the return value by calling g_time_zone_unref()
when you are done with it.
Returns
the requested timezone
Since: 2.26
g_time_zone_new_local ()
GTimeZone *
g_time_zone_new_local (void);
Creates a GTimeZone corresponding to local time. The local time
zone may change between invocations to this function; for example,
if the system administrator changes it.
This is equivalent to calling g_time_zone_new() with the value of
the TZ environment variable (including the possibility of NULL).
You should release the return value by calling g_time_zone_unref()
when you are done with it.
Returns
the local timezone
Since: 2.26
g_time_zone_new_utc ()
GTimeZone *
g_time_zone_new_utc (void);
Creates a GTimeZone corresponding to UTC.
This is equivalent to calling g_time_zone_new() with a value like
"Z", "UTC", "+00", etc.
You should release the return value by calling g_time_zone_unref()
when you are done with it.
Returns
the universal timezone
Since: 2.26
g_time_zone_new_offset ()
GTimeZone *
g_time_zone_new_offset (gint32 seconds);
Creates a GTimeZone corresponding to the given constant offset from UTC,
in seconds.
This is equivalent to calling g_time_zone_new() with a string in the form
[+|-]hh[:mm[:ss]].
Returns
a timezone at the given offset from UTC.
[transfer full]
Since: 2.58
g_time_zone_find_interval ()
gint
g_time_zone_find_interval (GTimeZone *tz,
GTimeType type,
gint64 time_);
Finds an interval within tz
that corresponds to the given time_
.
The meaning of time_
depends on type
.
If type
is G_TIME_TYPE_UNIVERSAL then this function will always
succeed (since universal time is monotonic and continuous).
Otherwise time_
is treated as local time. The distinction between
G_TIME_TYPE_STANDARD and G_TIME_TYPE_DAYLIGHT is ignored except in
the case that the given time_
is ambiguous. In Toronto, for example,
01:30 on November 7th 2010 occurred twice (once inside of daylight
savings time and the next, an hour later, outside of daylight savings
time). In this case, the different value of type
would result in a
different interval being returned.
It is still possible for this function to fail. In Toronto, for
example, 02:00 on March 14th 2010 does not exist (due to the leap
forward to begin daylight savings time). -1 is returned in that
case.
Returns
the interval containing time_
, or -1 in case of failure
Since: 2.26
g_time_zone_adjust_time ()
gint
g_time_zone_adjust_time (GTimeZone *tz,
GTimeType type,
gint64 *time_);
Finds an interval within tz
that corresponds to the given time_
,
possibly adjusting time_
if required to fit into an interval.
The meaning of time_
depends on type
.
This function is similar to g_time_zone_find_interval(), with the
difference that it always succeeds (by making the adjustments
described below).
In any of the cases where g_time_zone_find_interval() succeeds then
this function returns the same value, without modifying time_
.
This function may, however, modify time_
in order to deal with
non-existent times. If the non-existent local time_
of 02:30 were
requested on March 14th 2010 in Toronto then this function would
adjust time_
to be 03:00 and return the interval containing the
adjusted time.
Returns
the interval containing time_
, never -1
Since: 2.26
g_time_zone_get_identifier ()
const gchar *
g_time_zone_get_identifier (GTimeZone *tz);
Get the identifier of this GTimeZone, as passed to g_time_zone_new().
If the identifier passed at construction time was not recognised, UTC will
be returned. If it was NULL, the identifier of the local timezone at
construction time will be returned.
The identifier will be returned in the same format as provided at
construction time: if provided as a time offset, that will be returned by
this function.
Returns
identifier for this timezone
Since: 2.58
g_time_zone_get_abbreviation ()
const gchar *
g_time_zone_get_abbreviation (GTimeZone *tz,
gint interval);
Determines the time zone abbreviation to be used during a particular
interval
of time in the time zone tz
.
For example, in Toronto this is currently "EST" during the winter
months and "EDT" during the summer months when daylight savings time
is in effect.
Returns
the time zone abbreviation, which belongs to tz
Since: 2.26
g_time_zone_get_offset ()
gint32
g_time_zone_get_offset (GTimeZone *tz,
gint interval);
Determines the offset to UTC in effect during a particular interval
of time in the time zone tz
.
The offset is the number of seconds that you add to UTC time to
arrive at local time for tz
(ie: negative numbers for time zones
west of GMT, positive numbers for east).
Returns
the number of seconds that should be added to UTC to get the
local time in tz
Since: 2.26
g_time_zone_is_dst ()
gboolean
g_time_zone_is_dst (GTimeZone *tz,
gint interval);
Determines if daylight savings time is in effect during a particular
interval
of time in the time zone tz
.
Returns
TRUE if daylight savings time is in effect
Since: 2.26