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From: "Tom Linden" <tom@kednos.com>
Newsgroups: comp.lang.ada,comp.lang.fortran,comp.lang.pl1
Subject: Re: Ada vs Fortran for scientific applications
Date: Tue, 11 Jul 2006 06:53:04 -0700
Organization: Kednos
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Date: 2006-07-11T06:53:04-07:00
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On Mon, 10 Jul 2006 23:46:45 -0700, <adaworks@sbcglobal.net> wrote:

>
> "robin" <robin_v@bigpond.com> wrote in message
> news:z9Dsg.2740$tE5.2374@news-server.bigpond.net.au...
>>
>> Compilers can check for uninitialized variables during compilation.
>>
> True.  In fact, Ada compilers issue a warning for any variable
> that is used before a value is assigned to it.    If a parameter is
> included in a method (function/procedure/subroutine) and never
> referenced, a warning is issued.    Sometimes the pragma
> Normalize_Scalars is useful.   Often, the correct design is to
> leave variables uninitialized until they are used so an exception
> can be raised.   However, since the compiler will emit a warning
> about variables that have never been assigned a value in an algorithm
> that tries to use it, no harm is really done since the careful program=
mer
> will not release a program with warnings in it.

In general, this is not possible, and it is somewhat silly to have the  =

compiler
issue such messages, because on the average it will be wrong as often as=
  =

it is
right.  This can not be done at compile-time but must be done at run-tim=
e  =

and
it requires the compiler to generate a lot of machinery to produce such
mediocre messages.   Wht we did in PL/I was to produce in the  =

cross-reference
listing information on where a variable was referenced or assigned, but =
 =

this was
also somewhat incomplete because it requires a further analysis of  =

aliasing.  My
view is that it is of dubious value.


>
> So, I am assuming, Robin, that PL/I does something similar:  a warning=

> for any variable that is used in a program before a value is assigned =
to  =

> it.
>
> Richard Riehle
>
>