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From: Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP>
Newsgroups: comp.lang.ada
Subject: Re: How do I write directly to a memory address?
Date: Mon, 7 Feb 2011 12:42:35 +0000 (UTC)
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On 2011-02-07, Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> wrote:
>
> I think the "change the value of 4" reference above is literally that and
> does not mean changing a language accessible constant containing the value
> of 4.
>
> I made this mistake once with a old Fortran compiler when I was a student.
>
> The constant would be placed into a memory location somewhere by the Fortran
> compiler and then that memory location would be referenced at every point in
> the code in which the literal value (the integer 4 in this example) was used
> in a expression or a call to a subroutine.
>

I realised after posting, this was open to confusion by people who had not
encountered this before so a more detailed example follows. The word constant
above does not refer to a programmer defined constant, but a compiler defined
constant.

In the statement:

	c = (4 * i) + 2

the compiler would allocate memory locations containing the values 4 and 2.
These memory locations would then be used in the generated code whenever the
values of 2 or 4 were found. In other words, all access, including literals,
was by reference.

This was a long time ago however.

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world