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<!-- ##### SECTION Title ##### -->
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Date and Time Functions
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<!-- ##### SECTION Short_Description ##### -->
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calendrical calculations and miscellaneous time stuff.
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<!-- ##### SECTION Long_Description ##### -->
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The #GDate data structure represents a day between January 1, Year 1,
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and sometime a few thousand years in the future (right now it will go
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to the year 65535 or so, but g_date_set_parse() only parses up to the
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year 8000 or so - just count on "a few thousand"). #GDate is meant to
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represent everyday dates, not astronomical dates or historical dates
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or ISO timestamps or the like. It extrapolates the current Gregorian
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calendar forward and backward in time; there is no attempt to change
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the calendar to match time periods or locations. #GDate does not store
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time information; it represents a <emphasis>day</emphasis>.
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The #GDate implementation has several nice features; it is only a
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64-bit struct, so storing large numbers of dates is very efficient. It
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can keep both a Julian and day-month-year representation of the date,
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since some calculations are much easier with one representation or the
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other. A Julian representation is simply a count of days since some
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fixed day in the past; for #GDate the fixed day is January 1, 1 AD.
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("Julian" dates in the #GDate API aren't really Julian dates in the
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technical sense; technically, Julian dates count from the start of the
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Julian period, Jan 1, 4713 BC).
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#GDate is simple to use. First you need a "blank" date; you can get a
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dynamically allocated date from g_date_new(), or you can declare an
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automatic variable or array and initialize it to a sane state by
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calling g_date_clear(). A cleared date is sane; it's safe to call
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g_date_set_dmy() and the other mutator functions to initialize the
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value of a cleared date. However, a cleared date is initially
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<emphasis>invalid</emphasis>, meaning that it doesn't represent a day
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that exists. It is undefined to call any of the date calculation
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routines on an invalid date. If you obtain a date from a user or other
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unpredictable source, you should check its validity with the
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g_date_valid() predicate. g_date_valid() is also used to check for
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errors with g_date_set_parse() and other functions that can
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fail. Dates can be invalidated by calling g_date_clear() again.
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<emphasis>It is very important to use the API to access the #GDate
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struct.</emphasis> Often only the day-month-year or only the Julian
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representation is valid. Sometimes neither is valid. Use the API.
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GLib doesn't contain any time-manipulation functions; however, there
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is a #GTime typedef and a #GTimeVal struct which represents a more
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precise time (with microseconds). You can request the current time as
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a #GTimeVal with g_get_current_time().
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<!-- ##### SECTION See_Also ##### -->
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<!-- ##### SECTION Stability_Level ##### -->
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<!-- ##### MACRO G_USEC_PER_SEC ##### -->
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Number of microseconds in one second (1 million). This macro is provided for
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<!-- ##### STRUCT GTimeVal ##### -->
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Represents a precise time, with seconds and microseconds.
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Similar to the <structname>struct timeval</structname> returned by
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the <function>gettimeofday()</function> UNIX call.
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@tv_usec: microseconds.
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<!-- ##### FUNCTION g_get_current_time ##### -->
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<!-- ##### FUNCTION g_usleep ##### -->
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Pauses the current thread for the given number of microseconds. There
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are 1 million microseconds per second (represented by the
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#G_USEC_PER_SEC macro). g_usleep() may have limited precision,
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depending on hardware and operating system; don't rely on the exact
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@microseconds: number of microseconds to pause.
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<!-- ##### FUNCTION g_time_val_add ##### -->
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<!-- ##### FUNCTION g_time_val_from_iso8601 ##### -->
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<!-- ##### FUNCTION g_time_val_to_iso8601 ##### -->
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<!-- ##### STRUCT GDate ##### -->
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Represents a day between January 1, Year 1 and a few thousand years in
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the future. None of its members should be accessed directly. If the
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<structname>GDate</structname> is obtained from g_date_new(), it will
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be safe to mutate but invalid and thus not safe for calendrical computations.
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If it's declared on the stack, it will contain garbage so must be
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initialized with g_date_clear(). g_date_clear() makes the date invalid
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but sane. An invalid date doesn't represent a day, it's "empty." A
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date becomes valid after you set it to a Julian day or you set a day,
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@julian_days: the Julian representation of the date
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@julian: this bit is set if @julian_days is valid
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@dmy: this is set if @day, @month and @year are valid
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@day: the day of the day-month-year representation of the date, as
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a number between 1 and 31
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@month: the day of the day-month-year representation of the date, as
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a number between 1 and 12
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@year: the day of the day-month-year representation of the date
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<!-- ##### TYPEDEF GTime ##### -->
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Simply a replacement for <type>time_t</type>. It has been deprected
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since it is <emphasis>not</emphasis> equivalent to <type>time_t</type>
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on 64-bit platforms with a 64-bit <type>time_t</type>.
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Unrelated to #GTimer.
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Note that <type>GTime</type> is defined to always be a 32bit integer,
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unlike <type>time_t</type> which may be 64bit on some systems.
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Therefore, <type>GTime</type> will overflow in the year 2038, and
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you cannot use the address of a <type>GTime</type> variable as argument
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to the UNIX time() function. Instead, do the following:
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gtime = (GTime)ttime;
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<!-- ##### ENUM GDateDMY ##### -->
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This enumeration isn't used in the API, but may be useful if you need
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to mark a number as a day, month, or year.
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@G_DATE_MONTH: a month
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<!-- ##### TYPEDEF GDateDay ##### -->
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Integer representing a day of the month; between 1 and
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31. #G_DATE_BAD_DAY represents an invalid day of the month.
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<!-- ##### ENUM GDateMonth ##### -->
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Enumeration representing a month; values are #G_DATE_JANUARY,
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#G_DATE_FEBRUARY, etc. #G_DATE_BAD_MONTH is the invalid value.
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@G_DATE_BAD_MONTH: invalid value.
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@G_DATE_JANUARY: January.
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@G_DATE_FEBRUARY: February.
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@G_DATE_MARCH: March.
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@G_DATE_APRIL: April.
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@G_DATE_AUGUST: August.
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@G_DATE_SEPTEMBER: September.
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@G_DATE_OCTOBER: October.
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@G_DATE_NOVEMBER: November.
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@G_DATE_DECEMBER: December.
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<!-- ##### TYPEDEF GDateYear ##### -->
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Integer representing a year; #G_DATE_BAD_YEAR is the invalid
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value. The year must be 1 or higher; negative (BC) years are not
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allowed. The year is represented with four digits.
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<!-- ##### ENUM GDateWeekday ##### -->
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Enumeration representing a day of the week; #G_DATE_MONDAY,
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#G_DATE_TUESDAY, etc. #G_DATE_BAD_WEEKDAY is an invalid weekday.
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@G_DATE_BAD_WEEKDAY: invalid value.
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@G_DATE_MONDAY: Monday.
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@G_DATE_TUESDAY: Tuesday.
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@G_DATE_WEDNESDAY: Wednesday.
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@G_DATE_THURSDAY: Thursday.
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@G_DATE_FRIDAY: Friday.
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@G_DATE_SATURDAY: Saturday.
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@G_DATE_SUNDAY: Sunday.
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<!-- ##### MACRO G_DATE_BAD_DAY ##### -->
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Represents an invalid #GDateDay.
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<!-- ##### MACRO G_DATE_BAD_JULIAN ##### -->
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Represents an invalid Julian day number.
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<!-- ##### MACRO G_DATE_BAD_YEAR ##### -->
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Represents an invalid year.
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<!-- ##### FUNCTION g_date_new ##### -->
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Allocates a #GDate and initializes it to a sane state. The new date will
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be cleared (as if you'd called g_date_clear()) but invalid (it won't
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represent an existing day). Free the return value with g_date_free().
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@Returns: a newly-allocated #GDate.
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<!-- ##### FUNCTION g_date_new_dmy ##### -->
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Like g_date_new(), but also sets the value of the date. Assuming the
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day-month-year triplet you pass in represents an existing day, the
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returned date will be valid.
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@day: day of the month.
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@month: month of the year.
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@Returns: a newly-allocated #GDate initialized with @day, @month, and @year.
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<!-- ##### FUNCTION g_date_new_julian ##### -->
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Like g_date_new(), but also sets the value of the date. Assuming the
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Julian day number you pass in is valid (greater than 0, less than an
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unreasonably large number), the returned date will be valid.
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@julian_day: days since January 1, Year 1.
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@Returns: a newly-allocated #GDate initialized with @julian_day.
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<!-- ##### FUNCTION g_date_clear ##### -->
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Initializes one or more #GDate structs to a sane but invalid
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state. The cleared dates will not represent an existing date, but will
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not contain garbage. Useful to init a date declared on the stack.
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Validity can be tested with g_date_valid().
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@date: pointer to one or more dates to clear.
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@n_dates: number of dates to clear.
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<!-- ##### FUNCTION g_date_free ##### -->
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Frees a #GDate returned from g_date_new().
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<!-- ##### FUNCTION g_date_set_day ##### -->
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Sets the day of the month for a #GDate. If the resulting day-month-year
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triplet is invalid, the date will be invalid.
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<!-- ##### FUNCTION g_date_set_month ##### -->
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Sets the month of the year for a #GDate. If the resulting
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day-month-year triplet is invalid, the date will be invalid.
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@month: month to set.
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<!-- ##### FUNCTION g_date_set_year ##### -->
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Sets the year for a #GDate. If the resulting day-month-year triplet is
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invalid, the date will be invalid.
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<!-- ##### FUNCTION g_date_set_dmy ##### -->
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Sets the value of a #GDate from a day, month, and year. The day-month-year
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triplet must be valid; if you aren't sure it is, call g_date_valid_dmy() to
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check before you set it.
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<!-- ##### FUNCTION g_date_set_julian ##### -->
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Sets the value of a #GDate from a Julian day number.
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@julian_date: Julian day number (days since January 1, Year 1).
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<!-- ##### FUNCTION g_date_set_time ##### -->
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<!-- ##### FUNCTION g_date_set_time_t ##### -->
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<!-- ##### FUNCTION g_date_set_time_val ##### -->
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<!-- ##### FUNCTION g_date_set_parse ##### -->
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Parses a user-inputted string @str, and try to figure out what date it
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represents, taking the current locale into account. If the string is
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successfully parsed, the date will be valid after the call. Otherwise,
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it will be invalid. You should check using g_date_valid() to see
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whether the parsing succeeded.
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This function is not appropriate for file formats and the like; it
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isn't very precise, and its exact behavior varies with the
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locale. It's intended to be a heuristic routine that guesses what the
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user means by a given string (and it does work pretty well in that
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@date: a #GDate to fill in.
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@str: string to parse.
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<!-- ##### FUNCTION g_date_add_days ##### -->
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Increments a date some number of days. To move forward by weeks, add
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weeks*7 days. The date must be valid.
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@date: a #GDate to increment.
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@n_days: number of days to move the date forward.
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<!-- ##### FUNCTION g_date_subtract_days ##### -->
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Moves a date some number of days into the past. To move by weeks, just
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move by weeks*7 days. The date must be valid.
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@date: a #GDate to decrement.
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@n_days: number of days to move.
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<!-- ##### FUNCTION g_date_add_months ##### -->
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Increments a date by some number of months. If the day of the month is
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greater than 28, this routine may change the day of the month (because
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the destination month may not have the current day in it). The date
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@date: a #GDate to increment.
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@n_months: number of months to move forward.
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<!-- ##### FUNCTION g_date_subtract_months ##### -->
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Moves a date some number of months into the past. If the current day of
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the month doesn't exist in the destination month, the day of the month
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may change. The date must be valid.
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@date: a #GDate to decrement.
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@n_months: number of months to move.
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<!-- ##### FUNCTION g_date_add_years ##### -->
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Increments a date by some number of years. If the date is February 29,
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and the destination year is not a leap year, the date will be changed
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to February 28. The date must be valid.
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@date: a #GDate to increment.
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@n_years: number of years to move forward.
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<!-- ##### FUNCTION g_date_subtract_years ##### -->
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Moves a date some number of years into the past. If the current day
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doesn't exist in the destination year (i.e. it's February 29 and you
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move to a non-leap-year) then the day is changed to February 29. The date
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@date: a #GDate to decrement.
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@n_years: number of years to move.
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<!-- ##### FUNCTION g_date_days_between ##### -->
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Computes the number of days between two dates.
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If @date2 is prior to @date1, the returned value is negative.
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Both dates must be valid.
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@date1: the first date.
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@date2: the second date.
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@Returns: the number of days between @date1 and @date2.
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<!-- ##### FUNCTION g_date_compare ##### -->
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<function>qsort()</function>-style comparsion function for dates. Both
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@lhs: first date to compare.
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@rhs: second date to compare.
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@Returns: 0 for equal, less than zero if @lhs is less than @rhs,
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greater than zero if @lhs is greater than @rhs.
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<!-- ##### FUNCTION g_date_clamp ##### -->
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If @date is prior to @min_date, sets @date equal to @min_date.
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If @date falls after @max_date, sets @date equal to @max_date.
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Either @min_date and @max_date may be %NULL. All non-%NULL dates
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@date: a #GDate to clamp.
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@min_date: minimum accepted value for @date.
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@max_date: maximum accepted value for @date.
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<!-- ##### FUNCTION g_date_order ##### -->
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Checks if @date1 is less than or equal to @date2,
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and swap the values if this is not the case.
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@date1: the first date.
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@date2: the second date.
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<!-- ##### FUNCTION g_date_get_day ##### -->
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Returns the day of the month. The date must be valid.
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@date: a #GDate to extract the day of the month from.
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@Returns: day of the month.
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<!-- ##### FUNCTION g_date_get_month ##### -->
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Returns the month of the year. The date must be valid.
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@date: a #GDate to get the month from.
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@Returns: month of the year as a #GDateMonth.
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<!-- ##### FUNCTION g_date_get_year ##### -->
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Returns the year of a #GDate. The date must be valid.
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@Returns: year in which the date falls.
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<!-- ##### FUNCTION g_date_get_julian ##### -->
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Returns the Julian day or "serial number" of the #GDate. The
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Julian day is simply the number of days since January 1, Year 1; i.e.,
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January 1, Year 1 is Julian day 1; January 2, Year 1 is Julian day 2,
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etc. The date must be valid.
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@date: a #GDate to extract the Julian day from.
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@Returns: Julian day.
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<!-- ##### FUNCTION g_date_get_weekday ##### -->
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Returns the day of the week for a #GDate. The date must be valid.
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@Returns: day of the week as a #GDateWeekday.
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<!-- ##### FUNCTION g_date_get_day_of_year ##### -->
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Returns the day of the year, where Jan 1 is the first day of the
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year. The date must be valid.
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@date: a #GDate to extract day of year from.
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@Returns: day of the year.
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<!-- ##### FUNCTION g_date_get_days_in_month ##### -->
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Returns the number of days in a month, taking leap years into account.
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@Returns: number of days in @month during the @year.
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<!-- ##### FUNCTION g_date_is_first_of_month ##### -->
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Returns %TRUE if the date is on the first of a month. The date must be valid.
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@date: a #GDate to check.
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@Returns: %TRUE if the date is the first of the month.
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<!-- ##### FUNCTION g_date_is_last_of_month ##### -->
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Returns %TRUE if the date is the last day of the month. The date must be valid.
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@date: a #GDate to check.
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@Returns: %TRUE if the date is the last day of the month.
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<!-- ##### FUNCTION g_date_is_leap_year ##### -->
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Returns %TRUE if the year is a leap year.
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@year: year to check.
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@Returns: %TRUE if the year is a leap year.
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<!-- ##### FUNCTION g_date_get_monday_week_of_year ##### -->
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Returns the week of the year, where weeks are understood to start on
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Monday. If the date is before the first Monday of the year, return
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0. The date must be valid.
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@Returns: week of the year.
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<!-- ##### FUNCTION g_date_get_monday_weeks_in_year ##### -->
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Returns the number of weeks in the year, where weeks are taken to start
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on Monday. Will be 52 or 53. The date must be valid. (Years always have 52
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7-day periods, plus 1 or 2 extra days depending on whether it's a leap
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year. This function is basically telling you how many Mondays are in
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the year, i.e. there are 53 Mondays if one of the extra days happens
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@Returns: number of Mondays in the year.
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<!-- ##### FUNCTION g_date_get_sunday_week_of_year ##### -->
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Returns the week of the year during which this date falls, if weeks
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are understood to being on Sunday. The date must be valid. Can return 0 if
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the day is before the first Sunday of the year.
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@Returns: week number.
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<!-- ##### FUNCTION g_date_get_sunday_weeks_in_year ##### -->
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Returns the number of weeks in the year, where weeks are taken to start
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on Sunday. Will be 52 or 53. The date must be valid. (Years always have 52
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7-day periods, plus 1 or 2 extra days depending on whether it's a leap
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year. This function is basically telling you how many Sundays are in
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the year, i.e. there are 53 Sundays if one of the extra days happens
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@year: year to count weeks in.
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@Returns: number of weeks.
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<!-- ##### FUNCTION g_date_get_iso8601_week_of_year ##### -->
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<!-- ##### FUNCTION g_date_strftime ##### -->
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Generates a printed representation of the date, in a locale-specific
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way. Works just like the platform's C library
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<function>strftime()</function> function, but only accepts
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date-related formats; time-related formats give undefined
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results. Date must be valid. Unlike <function>strftime()</function>
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(which uses the locale encoding), works on a UTF-8 format string and
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stores a UTF-8 result.
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This function does not provide any conversion specifiers in addition
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to those implemented by the platform's C library. For example, don't
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expect that using <function>g_date_strftime()</function> would make
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the %F provided by the C99 <function>strftime()</function> work on
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Windows where the C library only complies to C89.
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@s: destination buffer.
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@format: format string.
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@Returns: number of characters written to the buffer, or 0 the buffer was too small.
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<!-- ##### FUNCTION g_date_to_struct_tm ##### -->
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Fills in the date-related bits of a <structname>struct tm</structname>
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using the @date value. Initializes the non-date parts with something
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sane but meaningless.
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@date: a #GDate to set the <structname>struct tm</structname> from.
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@tm: <structname>struct tm</structname> to fill.
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<!-- ##### FUNCTION g_date_valid ##### -->
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Returns %TRUE if the #GDate represents an existing day. The date must not
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contain garbage; it should have been initialized with g_date_clear()
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if it wasn't allocated by one of the g_date_new() variants.
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@date: a #GDate to check.
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@Returns: Whether the date is valid.
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<!-- ##### FUNCTION g_date_valid_day ##### -->
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Returns %TRUE if the day of the month is valid (a day is valid if it's
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between 1 and 31 inclusive).
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@Returns: %TRUE if the day is valid.
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<!-- ##### FUNCTION g_date_valid_month ##### -->
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Returns %TRUE if the month value is valid. The 12 #GDateMonth
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enumeration values are the only valid months.
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@Returns: %TRUE if the month is valid.
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<!-- ##### FUNCTION g_date_valid_year ##### -->
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Returns %TRUE if the year is valid. Any year greater than 0 is valid,
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though there is a 16-bit limit to what #GDate will understand.
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@Returns: %TRUE if the year is valid.
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<!-- ##### FUNCTION g_date_valid_dmy ##### -->
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Returns %TRUE if the day-month-year triplet forms a valid, existing day
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in the range of days #GDate understands (Year 1 or later, no more than
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a few thousand years in the future).
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@Returns: %TRUE if the date is a valid one.
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<!-- ##### FUNCTION g_date_valid_julian ##### -->
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Returns %TRUE if the Julian day is valid. Anything greater than zero is basically a
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valid Julian, though there is a 32-bit limit.
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@julian_date: Julian day to check.
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@Returns: %TRUE if the Julian day is valid.
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<!-- ##### FUNCTION g_date_valid_weekday ##### -->
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Returns %TRUE if the weekday is valid. The 7 #GDateWeekday enumeration
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values are the only valid weekdays.
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@Returns: %TRUE if the weekday is valid.
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docs/reference/glib/tmpl/date.sgml
