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Functions
void | g_time_zone_unref () |
GTimeZone * | g_time_zone_ref () |
GTimeZone * | g_time_zone_new () |
GTimeZone * | g_time_zone_new_local () |
GTimeZone * | g_time_zone_new_utc () |
gint | g_time_zone_find_interval () |
gint | g_time_zone_adjust_time () |
const gchar * | g_time_zone_get_abbreviation () |
gint32 | g_time_zone_get_offset () |
gboolean | g_time_zone_is_dst () |
Description
GTimeZone is a structure that represents a time zone, at no particular point in time. It is refcounted and immutable.
A time zone contains a number of intervals. Each interval has an abbreviation to describe it, 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.
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
.
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, or 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]" 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.
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.
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.
Since 2.26
g_time_zone_find_interval ()
gint g_time_zone_find_interval (GTimeZone *tz
,GTimeType type
,gint64 time_
);
Finds an the 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.
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.
Since 2.26
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.
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).
Since 2.26
Types and Values
GTimeZone
typedef struct _GTimeZone GTimeZone;
GTimeZone is an opaque structure whose members cannot be accessed directly.
Since 2.26
enum GTimeType
Disambiguates a given time in two ways.
First, specifies if the given time is in universal or local time.
Second, if the time is in local time, specifies if it is local standard time or local daylight time. This is important for the case where the same local time occurs twice (during daylight savings time transitions, for example).