Re: [Q] Returning Strings From A Function

[mheaney@ni.net (Matthew Heaney)]

In article <01bc43b8$a4c441a0$09f682c1@xhv46.dial.pipex.com>, "Nick
Roberts" <Nick.Roberts@dial.pipex.com> wrote:


>Argh! The embarrassment! Sudden brainstorm, Bob (my excuse being that I am
>using a lot of different languages at the moment (pretty feeble, eh?)).
>Anyway, what I _should_ have written was this...
>
>
>declare
>   F: Text_IO.File_Type;
>   ...
>   type Filename_String is array (1..12 range <>) of Character;
>   type Filename_Ref is access Filename_String;
>   ...
>   S: Filename_Ref;
>   ...
>begin
>   ...
>   S := new Filename_String'(Text_IO.Name(F)); -- constraint error raised
>if name longer than 12 chars
>   ...
>   Text_IO.Put("Name of file is: "+String(S.all)); -- note the need to
>dereference and convert
>   ...
>end;

Nick: 

This is an equally confusing solution.  No heap is required:

declare
   The_Name : String (1 .. 12);
begin
   The_Name := Text_IO.Name (F);
   -- This assignment will raise Constraint_Error if the length of the 
   -- return value is not _exactly_ 12.  (It could be lesser or greater.)

   Text_IO.Put ("Name is " & The_Name);
exception
   when Constraint_Error => ...;
end;

Two issues:

1.  Do not use heap when the stack will do.

2. Don't create new string types, ie use subtypes of Standard.String unless
you have a compelling need not to.  In this case, you wanted a string of
length 12, so just use Standard.String:

The_Name : String (1 .. 12);  -- an "anonymous" subtype

subtype Name_String is String (1 .. 12);
The_Name : Name_String;  -- a named subtype

KISS is the operative word.

Matt

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Matthew Heaney
Software Development Consultant
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