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Message-ID: <1417635789.4789.35.camel@eris.loria.fr>
Date: Wed, 03 Dec 2014 20:43:09 +0100
From: Jens Gustedt <jens.gustedt@...ia.fr>
To: musl@...ts.openwall.com
Subject: Re: getopt_long permutation algorithm questions
Am Mittwoch, den 03.12.2014, 14:29 -0500 schrieb Rich Felker:
> As part of resolving the rest of the dist-local changes Alpine is
> applying to musl, I'm trying to figure out how to add GNU-style
> argument permutation to getopt_long. The basic concept is simple: when
> a non-option argument is encountered, skip forward until the next
> option (argument beginning with '-') and move it (and possibly its
> argument) before the non-option arguments. However, there are some
> ugly corner cases like:
>
> arg1 -ab foo arg2
>
> where 'a' and 'b' are options, and 'b' takes an argument, foo. Here it
> seems like, in order to perform the correct permutation, lookahead is
> required to see that foo also needs to be moved. Is this correct?
>
> For long options, it's immediately decidable from the option being
> processed whether it has no argument, or an argument that's part of
> the same argv[] string, or a separate option in the next argv[] slot.
> For short options, it seems necessary to scan each character of the
> argv[] string to be moved, looking for the first option that takes an
> argument. If none is found, or if such a character is found in a
> non-final position, only this string needs to be moved. If an option
> needing an argument is found in the final position, two argv[] strings
> need to be moved. Is this correct?
sounds all a bit complicated and fragile to me. getopt should neither
be performance nor memory critical, so there is not much need for
optimization here, no?
Why don't you just keep track of the cases in an array on the stack,
and then do all the moves after the processing in a second scan? You
have argc, so you know the size of a VLA (`char[argc]` should suffice)
that you would have to define.
Jens
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