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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Empty String confusion; Positive and Natural
Date: Tue, 30 Nov 2021 10:34:56 +0200
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On 2021-11-30 0:50, Kevin Chadwick wrote:
>> It would clarify your question if you would show the declaration of that
>> record type. Does it use the String type, or the Unbounded_String type?
> 
> Hopefully I will have a doh moment when I get into the office in the
> morning and post code. I am getting a range check exception when I
> assign "" to a standard.String

Although Standard.String is an unconstrained array type (that is, its 
index range is defined as "Positive range <>"), every object of this 
type is constrained to a fixed length, set when the object is created.

So if you have, for example:

    S : String (1 .. 10);

then S'Length is always 10. If you try to assign to S a string of a 
different length, for example "", you will get an exception because the 
lengths do not match.

If you want a string object that is flexible in terms of length, you 
should use the type Ada.Strings.Unbounded.Unbounded_String, or make an 
instance of Ada.Strings.Bounded.Bounded_String with a suitable maximum 
length.

Or you could use a fixed-length string but always pad it with blanks (or 
whatever) up to the fixed length -- see Ada.Strings.Fixed for several 
useful operations on such strings. Depends on what you want...