Path: utzoo!utgpu!news-server.csri.toronto.edu!torsqnt!geac!alias!bmcphers
From: bmcphers@alias.UUCP (Brent McPherson)
Newsgroups: comp.lang.c++
Subject: Re: C++ coding standards (Comment needed)
Keywords: standard,variables
Message-ID: <1990Aug13.182226.24141@alias.uucp>
Date: 13 Aug 90 18:22:26 GMT
References: <2161@runxtsa.runx.oz.au>
Sender: news@alias.uucp (USENET News)
Organization: Alias Research Inc., Toronto ON Canada
Lines: 40

In article <2161@runxtsa.runx.oz.au> edward@runxtsa.runx.oz.au (Edward Birch) writes:
>A friend of mine works with a large organization where they have defined a
>standard that "variables must be declared where first used".
>
>I think that this is an absolutely insane standard for the following reasons:
>[reasons deleted]

I have to disagree with you. There are important reasons for not doing this
in C++.  If all variables in C++ were declared at the start of a routine,
then all the constructors/destructors would get executed on each invocation
of the routine (even if the variables are not used because of control flow
within the routine). The problem is also worse because of nested constructors
and destructors with inherited classes.

A better plan would be to declare all variables at the start of each block
so objects that aren't used (depending on which blocks are executed)
don't have their constructors/destructors called. This distributes the cost
evenly over the entire routine and can result in less overhead in most cases
(rather than a large, constant cost at entry/exit of the routine).

I also like having variables declared close to where they are used since you
will be less likely to forget to remove old variable declarations as the
code evolves. This is not so much of a problem these days since most compilers
will warn of unused/uninitialized variables.

Finally, common sense should prevail. If a variable is first assigned a value
within a loop it should be declared outside the loop just in case the compiler
decides to create the variable on the stack for each loop iteration.

BTW. I think constant cursoring to the top of a routine to add/delete/modify
variables increases development time. Also, readability/understandability are
a matter of personal preference (remember the brace/format/spacing debates
between various C programmers).

>Edward Birch

--
Brent McPherson
Alias Research Inc.
bmcphers%alias@csri.toronto.edu