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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Strings with discriminated records
Date: Sun, 27 May 2018 19:07:58 +0100
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Date: 2018-05-27T19:07:58+01:00
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NiGHTS <nights@unku.us> writes:

> I've expanded my example to include a strange run-time crash I am getting.
>
> Type Message (Length : Positive) is new Ada.Finalization.Controlled with record
>     Text  :  String (1 .. Length);
>     Cstr  :  Interfaces.C.Strings.chars_ptr;
> end record;
>        
> function Create (Value : String) return Message is
> begin
>     return (
>         Ada.Finalization.Controlled with Length => Value'Length, 
>         Text => Value, 
>         Cstr => Interfaces.C.Strings.New_String (Value) 
>     );
> end Create; 
>
> procedure Finalize (
>     M : in out Message
> ) is
> begin
>     Interfaces.C.Strings.Free ( M.Cstr ); -- Crashes here
> end;
>
> declare
>     M : Message := Create ("Hello World");
> begin
>     null;
> end; 
>
> Why does my program crash on Finalization?

Maybe Finalize is getting called twice? You should set M.Cstr to
Null_Ptr after freeing it.