Message-Id:	<199812260315.WAA30107@delorie.com>
Comments:	Authenticated sender is <mert0407 AT sable DOT ox DOT ac DOT uk>
From:	"George Foot" <george DOT foot AT merton DOT ox DOT ac DOT uk>
To:	Christian Hofrichter <ChristianHofrichter AT gmx DOT de>
Date:	Sat, 26 Dec 1998 03:14:46 +0000
MIME-Version:	1.0
Subject:	Re: void pointer arithmetic causes warning message
CC:	djgpp AT delorie DOT com
X-mailer:	Pegasus Mail for Win32 (v2.42a)
Reply-To:	djgpp AT delorie DOT com

On 25 Dec 98 at 21:23, Christian Hofrichter wrote:

> I have a void pointer and want to increase it by some bytes. Although I
> convert it into a char pointer I get a warning, everytime when compiling
> my code :
> "ANSI C++ forbids cast to non-reference type used as lvalue"
> 
> That not so bad, but how can I deactivate or avoid this message ?
> What I did is:
> (unsigned char*)pointer+=4;

Try:

    pointer = (char *)pointer + 4;

Casting in this way means the calculation is performed using
`char *'; the cast back to `void *' is implicit.

The warning generated by this:

    pointer = pointer + 4;

is only enabled if you use `-pedantic' switch or explicitly 
`-Wpointer-arith' in any case.  So, to turn it off try using 
the switch `-wpointer-arith' after your other options if 
possible.  I don't think this prevents the warning in 
`-pedantic' mode, so maybe you need to turn that off too.

Note that there's a reason why ANSI forbids arithmetic on void 
pointers -- I suggest you find a better way to do what you're 
doing, if possible.

-- 
george DOT foot AT merton DOT oxford DOT ac DOT uk

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