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Re: the signature of getopt, and getopt_long


From: Lorenzo Bettini
Subject: Re: the signature of getopt, and getopt_long
Date: Wed, 30 Sep 2009 18:40:50 +0200
User-agent: Thunderbird 2.0.0.23 (X11/20090817)

Hi

on a second thought, the cast is useless:

if I have a function

f(char **argv)

that passes argv to a function

g(char * const *argv)

there's no need to cast, since this does not issue any warning: I can pass something not const to something that expects something cost, can't I? It is the other way round which does not work...

am I right?
cheers
        Lorenzo

Sergey Poznyakoff wrote:
Hi Lorenzo,

the

char * const *argv

libc declaration of getopt_long (which looks wrong, since argv might
be changed during the parsing, right?)

Yes, it is wrong because argv might be permuted by getopt_long. And
that's why gnulib's implementation uses __getopt_argv_const in the
declaration (see the comment in lib/getopt.in.h:73).

now, I'd like to avoid the warning in the generated parser when using
gnulib, but I'd like to avoid it also when using libc getopt_long
version...

what would you suggest?

I believe typecasting to `char *__getopt_argv_const *___argv' would be
the best way to handle this. Keep in mind, though, that
__getopt_argv_const is a macro, which is defined only if you include
gnulib's version of getopt.h. Perhaps some additional #ifdef magic
would be required before the cast, e.g.:

#ifndef __getopt_argv_const
# define __getopt_argv_const const
#endif

Regards,
Sergey





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Lorenzo Bettini, PhD in Computer Science, DI, Univ. Torino
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