Formatting, Time Zones, and other operations for Time
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

Ada Reference Manual — Legal Information

# 9.6.1 Formatting, Time Zones, and other operations for Time

#### Static Semantics

1/2
The following language-defined library packages exist:
2/2
package Ada.Calendar.Time_Zones is
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-- Time zone manipulation:
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type Time_Offset is range -28*60 .. 28*60;
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Unknown_Zone_Error : exception;
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function UTC_Time_Offset (Date : Time := Clock) return Time_Offset;
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end Ada.Calendar.Time_Zones;
8/2
package Ada.Calendar.Arithmetic is
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-- Arithmetic on days:
10/2
type Day_Count is range
-366*(1+Year_Number'Last - Year_Number'First)
..
366*(1+Year_Number'Last - Year_Number'First);
11/2
subtype Leap_Seconds_Count is Integer range -2047 .. 2047;
12/2
procedure Difference (Left, Right : in Time;
Days : out Day_Count;
Seconds : out Duration;
Leap_Seconds : out Leap_Seconds_Count);
13/2
function "+" (Left : Time; Right : Day_Count) return Time;
function "+" (Left : Day_Count; Right : Time) return Time;
function "-" (Left : Time; Right : Day_Count) return Time;
function "-" (Left, Right : Time) return Day_Count;
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end Ada.Calendar.Arithmetic;
15/2
with Ada.Calendar.Time_Zones;
package Ada.Calendar.Formatting is
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-- Day of the week:
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type Day_Name is (Monday, Tuesday, Wednesday, Thursday,
Friday, Saturday, Sunday);
18/2
function Day_of_Week (Date : Time) return Day_Name;
19/2
-- Hours:Minutes:Seconds access:
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subtype Hour_Number is Natural range 0 .. 23;
subtype Minute_Number is Natural range 0 .. 59;
subtype Second_Number is Natural range 0 .. 59;
subtype Second_Duration is Day_Duration range 0.0 .. 1.0;
21/2
function Year (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Year_Number;
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function Month (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Month_Number;
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function Day (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Day_Number;
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function Hour (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Hour_Number;
25/2
function Minute (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Minute_Number;
26/2
function Second (Date : Time)
return Second_Number;
27/2
function Sub_Second (Date : Time)
return Second_Duration;
28/2
function Seconds_Of (Hour : Hour_Number;
Minute : Minute_Number;
Second : Second_Number := 0;
Sub_Second : Second_Duration := 0.0)
return Day_Duration;
29/2
procedure Split (Seconds : in Day_Duration;
Hour : out Hour_Number;
Minute : out Minute_Number;
Second : out Second_Number;
Sub_Second : out Second_Duration);
30/2
function Time_Of (Year : Year_Number;
Month : Month_Number;
Day : Day_Number;
Hour : Hour_Number;
Minute : Minute_Number;
Second : Second_Number;
Sub_Second : Second_Duration := 0.0;
Leap_Second: Boolean := False;
Time_Zone : Time_Zones.Time_Offset := 0)
return Time;
31/2
function Time_Of (Year : Year_Number;
Month : Month_Number;
Day : Day_Number;
Seconds : Day_Duration := 0.0;
Leap_Second: Boolean := False;
Time_Zone : Time_Zones.Time_Offset := 0)
return Time;
32/2
procedure Split (Date : in Time;
Year : out Year_Number;
Month : out Month_Number;
Day : out Day_Number;
Hour : out Hour_Number;
Minute : out Minute_Number;
Second : out Second_Number;
Sub_Second : out Second_Duration;
Time_Zone : in Time_Zones.Time_Offset := 0);
33/2
procedure Split (Date : in Time;
Year : out Year_Number;
Month : out Month_Number;
Day : out Day_Number;
Hour : out Hour_Number;
Minute : out Minute_Number;
Second : out Second_Number;
Sub_Second : out Second_Duration;
Leap_Second: out Boolean;
Time_Zone : in Time_Zones.Time_Offset := 0);
34/2
procedure Split (Date : in Time;
Year : out Year_Number;
Month : out Month_Number;
Day : out Day_Number;
Seconds : out Day_Duration;
Leap_Second: out Boolean;
Time_Zone : in Time_Zones.Time_Offset := 0);
35/2
-- Simple image and value:
function Image (Date : Time;
Include_Time_Fraction : Boolean := False;
Time_Zone : Time_Zones.Time_Offset := 0) return String;
36/2
function Value (Date : String;
Time_Zone : Time_Zones.Time_Offset := 0) return Time;
37/2
function Image (Elapsed_Time : Duration;
Include_Time_Fraction : Boolean := False) return String;
38/2
function Value (Elapsed_Time : String) return Duration;
39/2
end Ada.Calendar.Formatting;
40/2
Type Time_Offset represents the number of minutes difference between the implementation-defined time zone used by Calendar and another time zone.
41/2
function UTC_Time_Offset (Date : Time := Clock) return Time_Offset;
42/3
Returns, as a number of minutes, the result of subtracting the implementation-defined time zone of Calendar from UTC time, at the time Date. If the time zone of the Calendar implementation is unknown, then Unknown_Zone_Error is raised.
43/2
procedure Difference (Left, Right : in Time;
Days : out Day_Count;
Seconds : out Duration;
Leap_Seconds : out Leap_Seconds_Count);
44/2
Returns the difference between Left and Right. Days is the number of days of difference, Seconds is the remainder seconds of difference excluding leap seconds, and Leap_Seconds is the number of leap seconds. If Left < Right, then Seconds <= 0.0, Days <= 0, and Leap_Seconds <= 0. Otherwise, all values are nonnegative. The absolute value of Seconds is always less than 86_400.0. For the returned values, if Days = 0, then Seconds + Duration(Leap_Seconds) = Calendar."–" (Left, Right).
45/2
function "+" (Left : Time; Right : Day_Count) return Time;
function "+" (Left : Day_Count; Right : Time) return Time;
46/2
Adds a number of days to a time value. Time_Error is raised if the result is not representable as a value of type Time.
47/2
function "-" (Left : Time; Right : Day_Count) return Time;
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Subtracts a number of days from a time value. Time_Error is raised if the result is not representable as a value of type Time.
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function "-" (Left, Right : Time) return Day_Count;
50/2
Subtracts two time values, and returns the number of days between them. This is the same value that Difference would return in Days.
51/2
function Day_of_Week (Date : Time) return Day_Name;
52/2
Returns the day of the week for Time. This is based on the Year, Month, and Day values of Time.
53/2
function Year (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Year_Number;
54/2
Returns the year for Date, as appropriate for the specified time zone offset.
55/2
function Month (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Month_Number;
56/2
Returns the month for Date, as appropriate for the specified time zone offset.
57/2
function Day (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Day_Number;
58/2
Returns the day number for Date, as appropriate for the specified time zone offset.
59/2
function Hour (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Hour_Number;
60/2
Returns the hour for Date, as appropriate for the specified time zone offset.
61/2
function Minute (Date : Time;
Time_Zone : Time_Zones.Time_Offset := 0)
return Minute_Number;
62/2
Returns the minute within the hour for Date, as appropriate for the specified time zone offset.
63/2
function Second (Date : Time)
return Second_Number;
64/2
Returns the second within the hour and minute for Date.
65/2
function Sub_Second (Date : Time)
return Second_Duration;
66/2
Returns the fraction of second for Date (this has the same accuracy as Day_Duration). The value returned is always less than 1.0.
67/2
function Seconds_Of (Hour : Hour_Number;
Minute : Minute_Number;
Second : Second_Number := 0;
Sub_Second : Second_Duration := 0.0)
return Day_Duration;
68/2
Returns a Day_Duration value for the combination of the given Hour, Minute, Second, and Sub_Second. This value can be used in Calendar.Time_Of as well as the argument to Calendar."+" and Calendar."–". If Seconds_Of is called with a Sub_Second value of 1.0, the value returned is equal to the value of Seconds_Of for the next second with a Sub_Second value of 0.0.
69/2
procedure Split (Seconds : in Day_Duration;
Hour : out Hour_Number;
Minute : out Minute_Number;
Second : out Second_Number;
Sub_Second : out Second_Duration);
70/3
Splits Seconds into Hour, Minute, Second and Sub_Second in such a way that the resulting values all belong to their respective subtypes. The value returned in the Sub_Second parameter is always less than 1.0. If Seconds = 86400.0, Split propagates Time_Error.
71/2
function Time_Of (Year : Year_Number;
Month : Month_Number;
Day : Day_Number;
Hour : Hour_Number;
Minute : Minute_Number;
Second : Second_Number;
Sub_Second : Second_Duration := 0.0;
Leap_Second: Boolean := False;
Time_Zone : Time_Zones.Time_Offset := 0)
return Time;
72/2
If Leap_Second is False, returns a Time built from the date and time values, relative to the specified time zone offset. If Leap_Second is True, returns the Time that represents the time within the leap second that is one second later than the time specified by the other parameters. Time_Error is raised if the parameters do not form a proper date or time. If Time_Of is called with a Sub_Second value of 1.0, the value returned is equal to the value of Time_Of for the next second with a Sub_Second value of 0.0.
73/2
function Time_Of (Year : Year_Number;
Month : Month_Number;
Day : Day_Number;
Seconds : Day_Duration := 0.0;
Leap_Second: Boolean := False;
Time_Zone : Time_Zones.Time_Offset := 0)
return Time;
74/2
If Leap_Second is False, returns a Time built from the date and time values, relative to the specified time zone offset. If Leap_Second is True, returns the Time that represents the time within the leap second that is one second later than the time specified by the other parameters. Time_Error is raised if the parameters do not form a proper date or time. If Time_Of is called with a Seconds value of 86_400.0, the value returned is equal to the value of Time_Of for the next day with a Seconds value of 0.0.
75/2
procedure Split (Date : in Time;
Year : out Year_Number;
Month : out Month_Number;
Day : out Day_Number;
Hour : out Hour_Number;
Minute : out Minute_Number;
Second : out Second_Number;
Sub_Second : out Second_Duration;
Leap_Second: out Boolean;
Time_Zone : in Time_Zones.Time_Offset := 0);
76/2
If Date does not represent a time within a leap second, splits Date into its constituent parts (Year, Month, Day, Hour, Minute, Second, Sub_Second), relative to the specified time zone offset, and sets Leap_Second to False. If Date represents a time within a leap second, set the constituent parts to values corresponding to a time one second earlier than that given by Date, relative to the specified time zone offset, and sets Leap_Seconds to True. The value returned in the Sub_Second parameter is always less than 1.0.
77/2
procedure Split (Date : in Time;
Year : out Year_Number;
Month : out Month_Number;
Day : out Day_Number;
Hour : out Hour_Number;
Minute : out Minute_Number;
Second : out Second_Number;
Sub_Second : out Second_Duration;
Time_Zone : in Time_Zones.Time_Offset := 0);
78/2
Splits Date into its constituent parts (Year, Month, Day, Hour, Minute, Second, Sub_Second), relative to the specified time zone offset. The value returned in the Sub_Second parameter is always less than 1.0.
79/2
procedure Split (Date : in Time;
Year : out Year_Number;
Month : out Month_Number;
Day : out Day_Number;
Seconds : out Day_Duration;
Leap_Second: out Boolean;
Time_Zone : in Time_Zones.Time_Offset := 0);
80/2
If Date does not represent a time within a leap second, splits Date into its constituent parts (Year, Month, Day, Seconds), relative to the specified time zone offset, and sets Leap_Second to False. If Date represents a time within a leap second, set the constituent parts to values corresponding to a time one second earlier than that given by Date, relative to the specified time zone offset, and sets Leap_Seconds to True. The value returned in the Seconds parameter is always less than 86_400.0.
81/2
function Image (Date : Time;
Include_Time_Fraction : Boolean := False;
Time_Zone : Time_Zones.Time_Offset := 0) return String;
82/2
Returns a string form of the Date relative to the given Time_Zone. The format is "Year-Month-Day Hour:Minute:Second", where the Year is a 4-digit value, and all others are 2-digit values, of the functions defined in Calendar and Calendar.Formatting, including a leading zero, if needed. The separators between the values are a minus, another minus, a colon, and a single space between the Day and Hour. If Include_Time_Fraction is True, the integer part of Sub_Seconds*100 is suffixed to the string as a point followed by a 2-digit value.
83/2
function Value (Date : String;
Time_Zone : Time_Zones.Time_Offset := 0) return Time;
84/2
Returns a Time value for the image given as Date, relative to the given time zone. Constraint_Error is raised if the string is not formatted as described for Image, or the function cannot interpret the given string as a Time value.
85/2
function Image (Elapsed_Time : Duration;
Include_Time_Fraction : Boolean := False) return String;
86/2
Returns a string form of the Elapsed_Time. The format is "Hour:Minute:Second", where all values are 2-digit values, including a leading zero, if needed. The separators between the values are colons. If Include_Time_Fraction is True, the integer part of Sub_Seconds*100 is suffixed to the string as a point followed by a 2-digit value. If Elapsed_Time < 0.0, the result is Image (abs Elapsed_Time, Include_Time_Fraction) prefixed with a minus sign. If abs Elapsed_Time represents 100 hours or more, the result is implementation-defined.
87/2
function Value (Elapsed_Time : String) return Duration;
88/2
Returns a Duration value for the image given as Elapsed_Time. Constraint_Error is raised if the string is not formatted as described for Image, or the function cannot interpret the given string as a Duration value.

#### Implementation Advice

89/2
An implementation should support leap seconds if the target system supports them. If leap seconds are not supported, Difference should return zero for Leap_Seconds, Split should return False for Leap_Second, and Time_Of should raise Time_Error if Leap_Second is True.
NOTES
90/2
38 The implementation-defined time zone of package Calendar may, but need not, be the local time zone. UTC_Time_Offset always returns the difference relative to the implementation-defined time zone of package Calendar. If UTC_Time_Offset does not raise Unknown_Zone_Error, UTC time can be safely calculated (within the accuracy of the underlying time-base).
91/2
39 Calling Split on the results of subtracting Duration(UTC_Time_Offset*60) from Clock provides the components (hours, minutes, and so on) of the UTC time. In the United States, for example, UTC_Time_Offset will generally be negative.

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