Description
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 to a sane state by
calling g_date_clear(). A cleared date is sane; 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 DMY or only the Julian
representation is valid. Sometimes neither is valid. Use the API.
glib doesn't contain any time-manipulation functions; however, there
is a GTime typedef which is equivalent to time_t, and a GTimeVal
struct which represents a more precise time (with microseconds). You
can request the current time as a GTimeVal with g_get_current_time().
Details
struct GTimeVal
struct GTimeVal
{
glong tv_sec;
glong tv_usec;
}; |
Represents a precise time, with seconds and microseconds. Same as the
struct timeval returned by the
gettimeofday() UNIX call.
g_get_current_time ()
void g_get_current_time (GTimeVal *result); |
Equivalent to gettimeofday(), but also works on
Win32. Returns the current time.
struct GDate
struct GDate
{
guint julian_days : 32; /* julian days representation - we use a
* bitfield hoping that 64 bit platforms
* will pack this whole struct in one big
* int
*/
guint julian : 1; /* julian is valid */
guint dmy : 1; /* dmy is valid */
/* DMY representation */
guint day : 6;
guint month : 4;
guint year : 16;
}; |
Represents a day between January 1, Year 1 and a few thousand years in
the future. None of its members should be accessed directly. If the
GDate is obtained from g_date_new(), it will
be safe to mutate but invalid and thus not safe for calendrical computations.
If it's declared on the stack, it will contain garbage so must be
initialized with g_date_clear(). g_date_clear() makes the date invalid
but sane. An invalid date doesn't represent a day, it's "empty." A
date becomes valid after you set it to a Julian day or you set a day,
month, and year.
GTime
Simply a replacement for time_t. Unrelated to GTimer.
enum GDateDMY
typedef enum
{
G_DATE_DAY = 0,
G_DATE_MONTH = 1,
G_DATE_YEAR = 2
} GDateDMY; |
This enumeration isn't used in the API, but may be useful if you need
to mark a number as a day, month, or year.
GDateDay
typedef guint8 GDateDay; /* day of the month */ |
Integer representing a day of the month; between 1 and
31. G_DATE_BAD_DAY represents an invalid day of the month.
enum GDateMonth
typedef enum
{
G_DATE_BAD_MONTH = 0,
G_DATE_JANUARY = 1,
G_DATE_FEBRUARY = 2,
G_DATE_MARCH = 3,
G_DATE_APRIL = 4,
G_DATE_MAY = 5,
G_DATE_JUNE = 6,
G_DATE_JULY = 7,
G_DATE_AUGUST = 8,
G_DATE_SEPTEMBER = 9,
G_DATE_OCTOBER = 10,
G_DATE_NOVEMBER = 11,
G_DATE_DECEMBER = 12
} GDateMonth; |
Enumeration representing a month; values are G_DATE_JANUARY,
G_DATE_FEBRUARY, etc. G_DATE_BAD_MONTH is the "invalid" value.
GDateYear
typedef guint16 GDateYear; |
Integer representing a year; G_DATE_BAD_YEAR is the invalid
value. The year must be 1 or higher; negative (BC) years are not
allowed. The year is represented with four digits.
enum GDateWeekday
typedef enum
{
G_DATE_BAD_WEEKDAY = 0,
G_DATE_MONDAY = 1,
G_DATE_TUESDAY = 2,
G_DATE_WEDNESDAY = 3,
G_DATE_THURSDAY = 4,
G_DATE_FRIDAY = 5,
G_DATE_SATURDAY = 6,
G_DATE_SUNDAY = 7
} GDateWeekday; |
Enumeration representing a day of the week; G_DATE_MONDAY,
G_DATE_TUESDAY, etc. G_DATE_BAD_WEEKDAY is an invalid weekday.
G_DATE_BAD_DAY
#define G_DATE_BAD_DAY 0U |
Represents an invalid GDateDay.
G_DATE_BAD_JULIAN
#define G_DATE_BAD_JULIAN 0U |
Represents an invalid Julian day number.
G_DATE_BAD_YEAR
#define G_DATE_BAD_YEAR 0U |
Represents an invalid year.
g_date_new ()
GDate* g_date_new (void); |
Allocate a GDate and initialize it to a sane 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 ()
Like g_date_new(), but also sets the value of the date. Assuming the
day/month/year triplet you pass in represents an existing day, the
returned date will be valid.
g_date_new_julian ()
Like g_date_new(), but also sets the value of the date. Assuming the
Julian day number you pass in is valid (greater than 0, less than an
unreasonably large number), the returned date will be valid.
g_date_clear ()
Initialize one or more GDate structs to a sane 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_set_day ()
Set 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_month ()
Set 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_year ()
Set the year for a GDate. If the resulting day-month-year triplet is
invalid, the date will be invalid.
g_date_set_dmy ()
Set the value of a GDate from a day, month, and year. The DMY 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 ()
Set the value of a GDate from a Julian day number.
g_date_set_time ()
Set the value of a date from a GTime (time_t) value. To set the value
of a date to the current day, you could write:
g_date_set_parse ()
void g_date_set_parse (GDate *date,
const gchar *str); |
Parse a user-inputted string str, and try to figure out what date it
represents, taking the current locale 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.
This function is not appropriate for file formats and the like; it
isn't very precise, and its exact behavior varies with the
locale. It's intended to be a heuristic routine that guesses what the
user means by a given string (and it does work pretty well in that
capacity).
g_date_add_days ()
Increment a date some number of days. To move forward by weeks, add
weeks*7 days. The date must be valid.
g_date_subtract_days ()
void g_date_subtract_days (GDate *date,
guint n_days); |
Move a date some number of days into the past. To move by weeks, just
move by weeks*7 days. Date must be valid.
g_date_add_months ()
void g_date_add_months (GDate *date,
guint n_months); |
Increment 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_subtract_months ()
void g_date_subtract_months (GDate *date,
guint n_months); |
Move a date some number of months into the past. If the current day of
the month doesn't exist in the destination month, the day of the month
may change. Date must be valid.
g_date_add_years ()
void g_date_add_years (GDate *date,
guint n_years); |
Increment 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_subtract_years ()
void g_date_subtract_years (GDate *date,
guint n_years); |
Move a date some number of years into the past. If the current day
doesn't exist in the destination year (i.e. it's February 29 and you
move to a non-leap-year) then the day is changed to February 29. Date
must be valid.
g_date_compare ()
qsort()-style comparsion function for dates. Both
dates must be valid.
g_date_day ()
Return the day of the month; the GDate must be valid.
g_date_month ()
Accessor for the month of the year. Date must be valid.
g_date_year ()
Accessor; returns the year of a GDate. The date must be valid.
g_date_julian ()
Accessor, 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. Date must be valid.
g_date_weekday ()
Returns the day of the week for a GDate. The date must be valid.
g_date_day_of_year ()
Return the day of the year, where Jan 1 is the first day of the
year. Date must be valid.
g_date_days_in_month ()
Return the number of days in a month, taking leap years into account.
g_date_is_first_of_month ()
Returns TRUE if the date is on the first of a month. Date must be valid.
g_date_is_last_of_month ()
Returns TRUE if the date is the last day of the month. Date must be valid.
g_date_is_leap_year ()
Returns TRUE if the year is a leap year
g_date_monday_week_of_year ()
Return 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. Date must be valid.
g_date_monday_weeks_in_year ()
Return the number of weeks in the year, where weeks are taken to start
on Monday. Will be 52 or 53. 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_sunday_week_of_year ()
Week of the year during which this date falls, if weeks are understood
to being on Sunday. Date must be valid. Can return 0 if the day is
before the first Sunday of the year.
g_date_sunday_weeks_in_year ()
Return the number of weeks in the year, where weeks are taken to start
on Sunday. Will be 52 or 53. 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_strftime ()
Generate a printed representation of the date, in a locale-specific
way. Works just like the standard C strftime()
function, but only accepts date-related formats; time-related formats
give undefined results. Date must be valid.
g_date_to_struct_tm ()
void g_date_to_struct_tm (GDate *date,
struct tm *tm); |
Fills in the date-related bits of a struct tm
using the date value. Initializes the non-date parts with something
sane but meaningless.
g_date_valid ()
Returns TRUE if the GDate represents an existing day. GDate must not
contain garbage; it should have been initialized with g_date_clear()
if it wasn't allocated by one of the g_date_new() variants.
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_month ()
Returns TRUE if the month value is valid. The 12 GDateMonth
enumeration values are the only valid months.
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.
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_weekday ()
Returns TRUE if the weekday is valid. The 7 GDateWeekday enumeration
values are the only valid weekdays.