Struct

GLibDate

Description [src]

struct GDate {
  guint julian_days : 32;
  guint julian : 1;
  guint dmy : 1;
  guint day : 6;
  guint month : 4;
  guint year : 16;
}

GDate is a struct for calendrical calculations.

The GDate data structure represents a day between January 1, Year 1, and sometime a few thousand years in the future (right now it will go to the year 65535 or so, but g_date_set_parse() only parses up to the year 8000 or so - just count on “a few thousand”). GDate is meant to represent everyday dates, not astronomical dates or historical dates or ISO timestamps or the like. It extrapolates the current Gregorian calendar forward and backward in time; there is no attempt to change the calendar to match time periods or locations. GDate does not store time information; it represents a day.

The GDate implementation has several nice features; it is only a 64-bit struct, so storing large numbers of dates is very efficient. It can keep both a Julian and day-month-year representation of the date, since some calculations are much easier with one representation or the other. A Julian representation is simply a count of days since some fixed day in the past; for GDate the fixed day is January 1, 1 AD. (“Julian” dates in the GDate API aren’t really Julian dates in the technical sense; technically, Julian dates count from the start of the Julian period, Jan 1, 4713 BC).

GDate is simple to use. First you need a “blank” date; you can get a dynamically allocated date from g_date_new(), or you can declare an automatic variable or array and initialize it by calling g_date_clear(). A cleared date is safe; it’s safe to call g_date_set_dmy() and the other mutator functions to initialize the value of a cleared date. However, a cleared date is initially invalid, meaning that it doesn’t represent a day that exists. It is undefined to call any of the date calculation routines on an invalid date. If you obtain a date from a user or other unpredictable source, you should check its validity with the g_date_valid() predicate. g_date_valid() is also used to check for errors with g_date_set_parse() and other functions that can fail. Dates can be invalidated by calling g_date_clear() again.

It is very important to use the API to access the GDate struct. Often only the day-month-year or only the Julian representation is valid. Sometimes neither is valid. Use the API.

GLib also features GDateTime which represents a precise time.

Structure members

julian_days: The Julian representation of the date.
julian: This bit is set if julian_days is valid.
dmy: This is set if day, month and year are valid.
day: The day of the day-month-year representation of the date, as a number between 1 and 31.
month: The month of the day-month-year representation of the date, as a number between 1 and 12.
year: The year of the day-month-year representation of the date.

Constructors

g_date_new

Allocates a GDate and initializes it to a safe state. The new date will be cleared (as if you’d called g_date_clear()) but invalid (it won’t represent an existing day). Free the return value with g_date_free().

g_date_new_dmy

Create a new GDate representing the given day-month-year triplet.

g_date_new_julian

Create a new GDate representing the given Julian date.

Functions

g_date_get_days_in_month

Returns the number of days in a month, taking leap years into account.

g_date_get_monday_weeks_in_year

Returns the number of weeks in the year, where weeks are taken to start on Monday. Will be 52 or 53. The date must be valid. (Years always have 52 7-day periods, plus 1 or 2 extra days depending on whether it’s a leap year. This function is basically telling you how many Mondays are in the year, i.e. there are 53 Mondays if one of the extra days happens to be a Monday.).

g_date_get_sunday_weeks_in_year

Returns the number of weeks in the year, where weeks are taken to start on Sunday. Will be 52 or 53. The date must be valid. (Years always have 52 7-day periods, plus 1 or 2 extra days depending on whether it’s a leap year. This function is basically telling you how many Sundays are in the year, i.e. there are 53 Sundays if one of the extra days happens to be a Sunday.).

g_date_is_leap_year

Returns TRUE if the year is a leap year.

g_date_strftime

Generates a printed representation of the date, in a [locale][setlocale]-specific way. Works just like the platform’s C library strftime() function, but only accepts date-related formats; time-related formats give undefined results. Date must be valid. Unlike strftime() (which uses the locale encoding), works on a UTF-8 format string and stores a UTF-8 result.

g_date_valid_day

Returns TRUE if the day of the month is valid (a day is valid if it’s between 1 and 31 inclusive).

g_date_valid_dmy

Returns TRUE if the day-month-year triplet forms a valid, existing day in the range of days GDate understands (Year 1 or later, no more than a few thousand years in the future).

g_date_valid_julian

Returns TRUE if the Julian day is valid. Anything greater than zero is basically a valid Julian, though there is a 32-bit limit.

g_date_valid_month

Returns TRUE if the month value is valid. The 12 GDateMonth enumeration values are the only valid months.

g_date_valid_weekday

Returns TRUE if the weekday is valid. The seven GDateWeekday enumeration values are the only valid weekdays.

g_date_valid_year

Returns TRUE if the year is valid. Any year greater than 0 is valid, though there is a 16-bit limit to what GDate will understand.

Instance methods

g_date_add_days

Increments a date some number of days. To move forward by weeks, add weeks*7 days. The date must be valid.

g_date_add_months

Increments a date by some number of months. If the day of the month is greater than 28, this routine may change the day of the month (because the destination month may not have the current day in it). The date must be valid.

g_date_add_years

Increments a date by some number of years. If the date is February 29, and the destination year is not a leap year, the date will be changed to February 28. The date must be valid.

g_date_clamp

If date is prior to min_date, sets date equal to min_date. If date falls after max_date, sets date equal to max_date. Otherwise, date is unchanged. Either of min_date and max_date may be NULL. All non-NULL dates must be valid.

g_date_clear

Initializes one or more GDate structs to a safe but invalid state. The cleared dates will not represent an existing date, but will not contain garbage. Useful to init a date declared on the stack. Validity can be tested with g_date_valid().

g_date_compare

Qsort()-style comparison function for dates. Both dates must be valid.

g_date_copy

Copies a GDate to a newly-allocated GDate. If the input was invalid (as determined by g_date_valid()), the invalid state will be copied as is into the new object.

since: 2.56

g_date_days_between

Computes the number of days between two dates. If date2 is prior to date1, the returned value is negative. Both dates must be valid.

g_date_free

Frees a GDate returned from g_date_new().

g_date_get_day

Returns the day of the month. The date must be valid.

g_date_get_day_of_year

Returns the day of the year, where Jan 1 is the first day of the year. The date must be valid.

g_date_get_iso8601_week_of_year

Returns the week of the year, where weeks are interpreted according to ISO 8601.

since: 2.6

g_date_get_julian

Returns the Julian day or “serial number” of the GDate. The Julian day is simply the number of days since January 1, Year 1; i.e., January 1, Year 1 is Julian day 1; January 2, Year 1 is Julian day 2, etc. The date must be valid.

g_date_get_monday_week_of_year

Returns the week of the year, where weeks are understood to start on Monday. If the date is before the first Monday of the year, return 0. The date must be valid.

g_date_get_month

Returns the month of the year. The date must be valid.

g_date_get_sunday_week_of_year

Returns the week of the year during which this date falls, if weeks are understood to begin on Sunday. The date must be valid. Can return 0 if the day is before the first Sunday of the year.

g_date_get_weekday

Returns the day of the week for a GDate. The date must be valid.

g_date_get_year

Returns the year of a GDate. The date must be valid.

g_date_is_first_of_month

Returns TRUE if the date is on the first of a month. The date must be valid.

g_date_is_last_of_month

Returns TRUE if the date is the last day of the month. The date must be valid.

g_date_order

Checks if date1 is less than or equal to date2, and swap the values if this is not the case.

g_date_set_day

Sets the day of the month for a GDate. If the resulting day-month-year triplet is invalid, the date will be invalid.

g_date_set_dmy

Sets the value of a GDate from a day, month, and year. The day-month-year triplet must be valid; if you aren’t sure it is, call g_date_valid_dmy() to check before you set it.

g_date_set_julian

Sets the value of a GDate from a Julian day number.

g_date_set_month

Sets the month of the year for a GDate. If the resulting day-month-year triplet is invalid, the date will be invalid.

g_date_set_parse

Parses a user-inputted string str, and try to figure out what date it represents, taking the [current locale][setlocale] into account. If the string is successfully parsed, the date will be valid after the call. Otherwise, it will be invalid. You should check using g_date_valid() to see whether the parsing succeeded.