GTimeZone

GTimeZone — a structure representing a time zone

Types and Values

Includes

#include <glib.h>

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 .

Parameters

tz

a GTimeZone

 

Since: 2.26


g_time_zone_ref ()

GTimeZone *
g_time_zone_ref (GTimeZone *tz);

Increases the reference count on tz .

Parameters

tz

a GTimeZone

 

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, 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.

Parameters

identifier

a timezone identifier.

[nullable]

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_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.

Parameters

tz

a GTimeZone

 

type

the GTimeType of time_

 

time_

a number of seconds since January 1, 1970

 

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.

Parameters

tz

a GTimeZone

 

type

the GTimeType of time_

 

time_

a pointer to a number of seconds since January 1, 1970

 

Returns

the interval containing time_ , never -1

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.

Parameters

tz

a GTimeZone

 

interval

an interval within the timezone

 

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).

Parameters

tz

a GTimeZone

 

interval

an interval within the timezone

 

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 .

Parameters

tz

a GTimeZone

 

interval

an interval within the timezone

 

Returns

TRUE if daylight savings time is in effect

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).

Members

G_TIME_TYPE_STANDARD

the time is in local standard time

 

G_TIME_TYPE_DAYLIGHT

the time is in local daylight time

 

G_TIME_TYPE_UNIVERSAL

the time is in UTC

 

See Also

GDateTime