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From: Preben Randhol <randhol+news@pvv.org>
Newsgroups: comp.lang.ada
Subject: Re: Array and memory usage
Date: Sun, 9 Mar 2003 17:09:16 +0000 (UTC)
Organization: Norwegian university of science and technology
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Jeffrey Creem wrote:

> 
> I believe what you are seeing is not something that will happen under all
> OS's.
> 
> Linux uses a commit-on-us type memory manager. Even though you initialized
> your data, it probably was done in such a way that the memory was intialized
> within the ELF initialized data segment.
> 
> Under linux even something like
> 
> aa = malloc(A_BIG_NUMBER)
> 
> will not show all of the data as actually allocated until a process accesses
> each page of memory..
> 
> What you are seeing is partially a trick and partially real. It is not a
> direct effect of the language or compiler.
> 
> Whether or not you should write your programs to rely on it will depend on
> many factors.
> 
> Certainly on an embedded OS like vxWorks, your memory would be allocated and
> consumed immediately.

OK Thanks for clearing it up. I saw the effect last night so I decided
it was time for sleep as I thought I had done something else wrong. But
when I saw the same effect today I started wondering what the effect
was.

At any rate I think I'll stick with an array and set it to some number
that can be changed if needed. We are not talking about a lot of bytes
anyway :-)

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