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From: "John B. Matthews" <nospam@nospam.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Vectors.Insert_Space bug?
Date: Wed, 20 May 2009 21:56:44 -0400
Organization: The Wasteland
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Date: 2009-05-20T21:56:44-04:00
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In article <4a146f41$0$90265$14726298@news.sunsite.dk>,
 Thomas Løcke <thomas.granvej6@gmail.com> wrote:

> I've stumbled on some weird behavior while trying to make use of the 
> Ada.Containers.Vectors.Insert_Space procedure. According to the RM, this 
> is what it should do:
> 
> "... Then Insert_Space slides the elements in the range Before .. 
> Last_Index (Container) up by Count positions, and then inserts empty 
> elements in the positions starting at Before."
> 
> But that is not at all what I'm seeing, as this small test-program will 
> show:
[...]
> The output from the Test program is:
> 
>   1 Item 1
>   2 Item 2
>   3 Item 3
>   4 Item 4
>   5 Item 5
>   6
>   7
>   8 Item 5
> 
> Which IMHO is wrong. There shouldn't be two "Item 5" elements. And it's 
> possible to make it even worse, by calling Insert_Space multiple times 
> with different Before and Count parameters.
> 
> It seems as if the element located at the Before index is copied and 
> inserted as the first new element, and only after that, does 
> Insert_Space actually start inserting empty elements.
> 
> I've tried to compile with two different compilers, and both exhibit 
> this odd behavior:
> 	GNATMAKE 4.2.3
> 	GNATMAKE  GPL 2008 (20080521)
> 
> I admit to just being a hobbyist, so this might just be me not "getting" 
> what the RM is trying to tell me, but I do think the text is fairly clear.
> 
> Any help would be greatly appreciated.

I get the same result with 4.3.4.

It looks like the old element 5 slid to position 8. The three empties 
are at positions 5, 6 and 7. Note that "Empty elements do not have a 
specified value." In particular, "Reading the value of an empty element 
by calling Element" is a bounded error, and "The implementation may 
treat the [empty] element as having any normal value...":

<http://www.adaic.com/standards/05rm/html/RM-A-18-2.html>

-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>