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From: Nick Roberts <nick.roberts@acm.org>
Newsgroups: comp.lang.ada
Subject: Re: ada calendar
Date: Tue, 09 Dec 2003 04:48:10 +0000
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Date: 2003-12-09T04:48:10+00:00
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Pascal Obry wrote:

> Marius Amado Alves <amado.alves@netcabo.pt> writes:
> 
>>You can do it with Ada.Calendar:
>>
>>  Your_Function (Time_Of
>>    (Year_Number'Value (S (7 .. 10)),
>>     Month_Number'Value (S (4 .. 5)),
>>     Day_Number'Value (S (1 .. 2))));
>>
>>where S is your string containing "27/06/2003" or similar.
> 
> There is no guarantee that S start to 1. It should be using S'First as
> offset to compute all slices.

True, but there's an alternative technique, and possibly a better one in 
this kind of case, using implicit array conversion:

    subtype Date_String is String(1..10);
    X: constant Date_String := S; -- checks length and slides if necessary
    ...
    if X(3) /= '/' or X(6) /= '/' then raise ...; end if;
    Your_Function( Time_Of( Year_Number'Value ( X(7..10) ),
                            Month_Number'Value( X(4..5)  ),
                            Day_Number'Value  ( X(1..2)  ) ) );

Obviously, if possible, it is desirable to declare S itself of a subtype 
such as Date_String.

This technique shows the person reading (reviewing) the code that X does 
indeed start at 1. If the declaration of Date_String is distant from the 
use of a variable of this subtype, you can always use an 'if' test (or 
pragma Assert, or a comment) to reiterate that the bounds are 1 and 10.

-- 
Nick Roberts