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Subject: Re: Bounded String question
Newsgroups: comp.lang.ada
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From: Xavier Petit <xpetit@becoast.fr>
Date: Sun, 6 Mar 2016 19:59:46 +0100
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Xref: news.eternal-september.org comp.lang.ada:29687
Date: 2016-03-06T19:59:46+01:00
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Le 11/11/2015 16:34, Bob Duff a écrit :
> No, the type is limited, so GNAT will allocate space for Max_Length
> characters, not Natural'Last characters.
>
> - Bob
>

Hello, I have noticed a problem with this technique, and I would like
to know if it is normal or a GNAT problem. With this source code =>

procedure Test_Bounded_String is
    package Bounded_String is
       type T (Max_Length : Natural := 100) is limited private;

    private
       type T (Max_Length : Natural := 100) is limited record
	 Length : Natural := 0;
	 Chars  : String (1 .. Max_Length);
       end record;
    end Bounded_String;

    Test : Bounded_String.T;

begin
    null;
end Test_Bounded_String;

$ gnatmake test_bounded_string.adb
gcc-5 -c test_bounded_string.adb
test_bounded_string.adb:12:04: warning: variable "Test" is never read
and never assigned
gnatbind-5 -x test_bounded_string.ali
gnatlink-5 test_bounded_string.ali
$ ./test_bounded_string

raised STORAGE_ERROR : stack overflow or erroneous memory access


But, if the type "T" is publicly fully declared, then all goes well :

    package Bounded_String is
       type T (Max_Length : Natural := 100) is limited record
	 Length : Natural := 0;
	 Chars  : String (1 .. Max_Length);
       end record;
    end Bounded_String;


$ gnatmake --version
GNATMAKE 5.3.1

$ cat /etc/debian_version
stretch/sid

$ apt-cache show gnat-5
Package: gnat-5
Source: gcc-5
Version: 5.3.1-8

$ cat /proc/version
Linux version 4.3.0-1-amd64 (debian-kernel@lists.debian.org) (gcc
version 5.3.1 20160121 (Debian 5.3.1-7) ) #1 SMP Debian 4.3.5-1 (2016-02-06)

The problem also occurs with GNAT 4.9.2 from Debian stable.
Thanks by advance !

-- 
Xavier Petit