From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Thu, 02 Nov 2006 09:15:12 GMT
Subject: Re: weird strncmp usage?
Message-ID: <Pine.LNX.4.63.0611021008180.1670@wbgn013.biozentrum.uni-wuerzburg.de>
In-Reply-To: <20061102065127.GA23105@coredump.intra.peff.net>

Hi,

On Thu, 2 Nov 2006, Jeff King wrote:

> On Thu, Nov 02, 2006 at 01:44:36AM +0000, Andy Whitcroft wrote:
> 
> > That said if you know its constant you can also use sizeof("foo") and
> > that is done at compile time.  Something like:
> > 
> > #define strxcmp(x, y)	strncmp((x), (y), sizeof((y))
> 
> You would, of course, need to use sizeof(y)-1 to avoid comparing the NUL
> termination. :)
> 
> This is a slightly dangerous macro, because it _only_ works for string
> literals, but not pointers (which is fine in this case, but its
> limitations need to be documented).

It would be even better to avoid these errors by doing something like

	#define starts_with(x, y) !strncmp((x), #y, sizeof(#y) - 1)

which would be used like this:

	if (starts_with(arg, --abbrev=))

However, in this case, you would need another macro, which automatically 
extracts the argument, and soon you will end up with yet another getopt 
package.

Ciao,
Dscho