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From: Ron Natalie <ron@sensor.com>
Subject: Re: Programming language vote - results
Date: 1997/11/26
Message-ID: <347C420A.2B18@sensor.com>#1/1
X-Deja-AN: 292875605
References: <3470EF6E.F74@lysator.liu.se>
 <64qsf0$ccc@dfw-ixnews11.ix.netcom.com> <347440AD.35DF@idt.net>
 <65di3v$730$1@news1.ucsd.edu>
Organization: Sensor Systems
Newsgroups: comp.lang.ada,comp.lang.apl,comp.lang.c,comp.lang.c++
Date: 1997-11-26T00:00:00+00:00
List-Id: <comp.lang.ada>


William Tanksley wrote:
> 
> 
> According to the ANSI standard and K&R, as well as universal prior
> practice, the boolean logical operators are short-circuiting.  This
> means that they MUST exectute in order.  In fact, this is required
> explicitly by ANSI and K&R.

The spec calls these sequence points.  Furthermore, && and ||
are required not to execute the right operand if the left
side evaluates to false (in the case of and) or true (in the
case of or).

> The malloc example *probably* has enough parentheses to force it to
> work in the right order but the fact is that the code is obscure at
> best and wrong at worst. It is also no more efficient when compiled
> than the equivalent construct:

Assuming to is a pointer, there's nothing wrong with the statement
as written by the original poster.  PARENS do NOT AFFECT ORDERING
in C/C++, they only affect the binding of the operations.

> It'll work, so long as the library returns zeroes for nulls.

It works no matter what.  The constant zero is the null pointer
constant.  If malloc returns a null pointer regardless of it's
machine representation, testing it for equality against an
integer zero (or the boolean not) will work.