From mboxrd@z Thu Jan  1 00:00:00 1970
From: Richard Earnshaw <rearnsha@arm.com>
To: Bill Currie <bcurrie@tssc.co.nz>
Cc: rearnsha@sun52.arm.com
Subject: Re: suggest parentheses around assignment used as truth value 
Date: Thu, 02 Jul 1998 07:08:00 -0000
Message-id: <199807021119.MAA19946@sun52.NIS.cambridge>
References: <359B0985.2FB4@tssc.co.nz>
X-SW-Source: 1998-07/msg00084.html

> Richard Earnshaw wrote:
> >         if ((x = p()) != 0) {...}
> > 
> > Then it becomes clear why the extra parentheses are needed.
> 
> Yes, because without the parentheses, it will be evaluated as:
> 
> 	if (x = (p() != 0)) {...}
> 
> And you're right back where you started from with a `suggest parentheses
> around assignment used as truth value' warning.
> 

Of course the parentheses are necessary in that case, but the meaning is 
obvious, and the compiler can tell that a warning is unnecessary.

In my opinion, it's a bug if gcc doesn't emit a warning for 

  if ((x = p())) {...}

but does for

  if (x = p()) {...}

since apart from an extra set of parentheses they are identical.  Perhaps 
the warning should be changed to "suggest explicit comparison of 
assignment used as truth value".


Richard.