Date Utilities

The Util.Dates package provides various date utilities to help in formatting and parsing dates in various standard formats. It completes the standard Ada.Calendar.Formatting and other packages by implementing specific formatting and parsing. To use the packages described here, use the following GNAT project:

with "utilada_base";

Date Operations

Several operations allow to compute from a given date:

  • Get_Day_Start: The start of the day (0:00),

  • Get_Day_End: The end of the day (23:59:59),

  • Get_Week_Start: The start of the week,

  • Get_Week_End: The end of the week,

  • Get_Month_Start: The start of the month,

  • Get_Month_End: The end of the month

The Date_Record type represents a date in a split format allowing to access easily the day, month, hour and other information.

Now        : Ada.Calendar.Time := Ada.Calendar.Clock;
Week_Start : Ada.Calendar.Time := Get_Week_Start (Now);
Week_End   : Ada.Calendar.Time := Get_Week_End (Now);

RFC7231 Dates

The RFC 7231 defines a standard date format that is used by HTTP headers. The Util.Dates.RFC7231 package provides an Image function to convert a date into that target format and a Value function to parse such format string and return the date.

  Now  : constant Ada.Calendar.Time := Ada.Calendar.Clock;
  S    : constant String := Util.Dates.RFC7231.Image (Now);
  Date : Ada.Calendar.time := Util.Dates.RFC7231.Value (S);

A Constraint_Error exception is raised when the date string is not in the correct format.

ISO8601 Dates

The ISO8601 defines a standard date format that is commonly used and easily parsed by programs. The Util.Dates.ISO8601 package provides an Image function to convert a date into that target format and a Value function to parse such format string and return the date.

  Now  : constant Ada.Calendar.Time := Ada.Calendar.Clock;
  S    : constant String := Util.Dates.ISO8601.Image (Now);
  Date : Ada.Calendar.time := Util.Dates.ISO8601.Value (S);

A Constraint_Error exception is raised when the date string is not in the correct format.

Localized date formatting

The Util.Dates.Formats provides a date formatting and parsing operation similar to the Unix strftime, strptime or the GNAT.Calendar.Time_IO. The localization of month and day labels is however handled through Util.Properties.Bundle (similar to the Java world). Unlike strftime and strptime, this allows to have a multi-threaded application that reports dates in several languages. The GNAT.Calendar.Time_IO only supports English and this is the reason why it is not used here.

The date pattern recognizes the following formats:

Format Description
%a The abbreviated weekday name according to the current locale.
%A The full weekday name according to the current locale.
%b The abbreviated month name according to the current locale.
%h Equivalent to %b. (SU)
%B The full month name according to the current locale.
%c The preferred date and time representation for the current locale.
%C The century number (year/100) as a 2-digit integer. (SU)
%d The day of the month as a decimal number (range 01 to 31).
%D Equivalent to %m/%d/%y
%e Like %d, the day of the month as a decimal number,
but a leading zero is replaced by a space. (SU)
%F Equivalent to %Y-%m-%d (the ISO 8601 date format). (C99)
%G The ISO 8601 week-based year
%H The hour as a decimal number using a 24-hour clock (range 00 to 23).
%I The hour as a decimal number using a 12-hour clock (range 01 to 12).
%j The day of the year as a decimal number (range 001 to 366).
%k The hour (24 hour clock) as a decimal number (range 0 to 23);
%l The hour (12 hour clock) as a decimal number (range 1 to 12);
%m The month as a decimal number (range 01 to 12).
%M The minute as a decimal number (range 00 to 59).
%n A newline character. (SU)
%p Either "AM" or "PM"
%P Like %p but in lowercase: "am" or "pm"
%r The time in a.m. or p.m. notation.
In the POSIX locale this is equivalent to %I:%M:%S %p. (SU)
%R The time in 24 hour notation (%H:%M).
%s The number of seconds since the Epoch, that is,
since 1970-01-01 00:00:00 UTC. (TZ)
%S The second as a decimal number (range 00 to 60).
%t A tab character. (SU)
%T The time in 24 hour notation (%H:%M:%S). (SU)
%u The day of the week as a decimal, range 1 to 7,
Monday being 1. See also %w. (SU)
%U The week number of the current year as a decimal
number, range 00 to 53
%V The ISO 8601 week number
%w The day of the week as a decimal, range 0 to 6,
Sunday being 0. See also %u.
%W The week number of the current year as a decimal number,
range 00 to 53
%x The preferred date representation for the current locale
without the time.
%X The preferred time representation for the current locale
without the date.
%y The year as a decimal number without a century (range 00 to 99).
%Y The year as a decimal number including the century.
%z The timezone as hour offset from GMT.
%Z The timezone or name or abbreviation.

The following strftime flags are ignored:

Format Description
%E Modifier: use alternative format, see below. (SU)
%O Modifier: use alternative format, see below. (SU)

SU: Single Unix Specification C99: C99 standard, POSIX.1-2001

See strftime (3) and strptime (3) manual page

To format and use the localize date, it is first necessary to get a bundle for the dates so that date elements are translated into the given locale.

 Factory     : Util.Properties.Bundles.Loader;
 Bundle      : Util.Properties.Bundles.Manager;
 ...
    Load_Bundle (Factory, "dates", "fr", Bundle);

The date is formatted according to the pattern string described above. The bundle is used by the formatter to use the day and month names in the expected locale.

 Date : String := Util.Dates.Formats.Format (Pattern => Pattern,
                                             Date    => Ada.Calendar.Clock,
                                             Bundle  => Bundle);

To parse a date according to a pattern and a localization, the same pattern string and bundle can be used and the Parse function will return the date in split format.

 Result : Date_Record := Util.Dates.Formats.Parse (Date    => Date,
                                                   Pattern => Pattern,
                                                   Bundle  => Bundle);