linux-kernel - sizeof vs strlen (was Re: [PATCH 4/4] fs/qnx4: decrement sizeof size in strncmp)

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Date:	Thu, 12 Nov 2009 11:22:15 +0100
From:	Bernd Petrovitsch <bernd@...mix.at>
To:	Julia Lawall <julia@...u.dk>
Cc:	al@...rsen.net, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: sizeof vs strlen (was Re: [PATCH 4/4] fs/qnx4: decrement sizeof
 size in strncmp)

On Thu, 2009-11-12 at 08:49 +0100, Julia Lawall wrote:
> From: Julia Lawall <julia@...u.dk>
> 
> As observed by Joe Perches, sizeof of a constant string includes the
> trailing 0.  If what is wanted is to check the initial characters of
> another string, this trailing 0 should not be taken into account.  If an
> exact match is wanted, strcmp should be used instead.
[...]
> strncmp(foo, abc, 
> - sizeof(abc)
> + sizeof(abc)-1
>  )
> // </smpl>
Am I the only one who find "strlen()" instead of "sizeof()-1" here much
more readable (and to the point).

As for run-time, it shouldn't make a difference for static/constant
strings as gcc should be able calculate the length at compile time. And
if the string is not constant, sizeof() is probably wrong anyways.

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
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