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Date: Thu, 8 Jul 2021 18:49:29 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: "Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>
Cc: Jonny Grant <jg@jguk.org>, gcc-help@gcc.gnu.org,
 linux-man <linux-man@vger.kernel.org>, Florian Weimer <fw@deneb.enyo.de>,
 Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: strlen
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On Thu, Jul 08, 2021 at 01:06:17PM +0200, Alejandro Colomar (man-pages) via Gcc-help wrote:
> On 7/8/21 12:07 PM, Jonny Grant wrote:
> >We can't guarantee safestrlen() won't be called with NULL. So because 
> >strlen() itself doesn't check for NULL in C standard we'd need to call the 
> >wrapper so that NULL can be checked for.

> >size_t __attribute__((optimize("O0"))) safestrlen(const char * s)
> >{
> >     if (NULL == s) return 0;
> >     else return strlen(s);
> >}

> That also allows differentiating a length of 0 (i.e., "") from an 
> invalid string (i.e., NULL), by returning -1 for NULL.

It is incorrect to return any particular value for strlen(0); not 0, not
-1, not anything.  Since there *is* no string, it doesn't have a length
either.

So instead of making some function for this, I recommend just writing
something like

  bla = s ? strlen(s) : 0;

wherever you need it.  If a function name isn't self-explanatory, and
even *cannot* be, your factoring is most likely not ideal.  Code is
primarily there for humans to read, it should be optimised for that.


Segher