Date: Wed, 19 Feb 97 17:05:29 CST From: Joe Greco <jgreco@solaria.sol.net> To: guido@gvr.win.tue.nl (Guido van Rooij) Cc: top@sonic.cris.net, audit-bin@freebsd.org, FreeBSD-hackers@freebsd.org Subject: Re: hmm Message-ID: <199702192305.RAA08083@solaria.sol.net> In-Reply-To: <199702192053.VAA02956@gvr.win.tue.nl> from "Guido van Rooij" at Feb 19, 97 09:53:45 pm
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> > char *p;
> >
> > if ((p = argv[0]) == NULL)
> > errx(2,"test: argc is zero");
Sanity check? I can't think of any cases where this would happen, but
maybe some kernel god would correct me.
> It seems a bit strange to me. Just like the first part of the line
> underneath btw:
> if (*p != '\0' && p[strlen(p) - 1] == '[') {
> ^^^^^^^^^^
That's sort of obvious, at least in the context of the second part
of the expression...
If you want to see if the last character in a string is '[', that is a
very fast way to do it ( p[strlen(p) - 1] == '[' ). However, in the case
where *p points to a zero-length string (i.e. argc[1] = ""), the expression
evaluates to an invalid case: strlen(p) = 0, and 0 - 1 = -1. Taking
the -1'th element of p[] is WRONG WRONG WRONG. But the ONLY time that
this can happen is if you have a null string. So check for it first.
It's simply a test looking for an argument that ends with the character
'['. It is precisely correct, with the assumption that p is a valid,
non-NULL, null terminated string of some sort.
(Alternate way to think of it: If you have a zero length string, it
obviously can not end in '[')
... Joe
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Joe Greco - Systems Administrator jgreco@ns.sol.net
Solaria Public Access UNIX - Milwaukee, WI 414/342-4847
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