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Date: Sat, 15 Dec 2012 05:21:19 +0400
From: Solar Designer <>
Subject: Re: Use of strnlen()

On Sat, Dec 15, 2012 at 01:51:07AM +0100, magnum wrote:
> I tried "#define _XOPEN_SOURCE 700" right before including string.h but it made no difference.

Feature macros need to be defined before the very first #include
directive, not before the "relevant" one.  Chances are that it was too
late to change them at the point where you put the #define.

> And this seem to be a late extension... is there any way I could conditionally use strnlen and fallback to strlen?

I'd rather avoid using strnlen() in all cases.  Chances are that for the
very low lengths that we're dealing with a custom loop is faster anyway.

Additionally, our own code may safely read beyond the NUL byte (if we
know that our buffer is large enough and we only need to check if the
length is sufficient, not find out the exact length) - this is something
we may make use of (e.g., check two chars per loop iteration, without
bothering about possibly crossing page boundary like libc would have to).

In fact, the length could be checked in rules_apply(), where it's
readily known.  Passing an extra argument to that function would have
performance impact when there's no minimum length specified, though.


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