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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: Jaakko Heinonen <jh@FreeBSD.org>
References: <4C16C5B5.1070308@FreeBSD.org>
	<20100616190416.GA3896@a91-153-117-195.elisa-laajakaista.fi>
Date: Wed, 16 Jun 2010 22:07:58 +0200
In-Reply-To: <20100616190416.GA3896@a91-153-117-195.elisa-laajakaista.fi>
	(Jaakko Heinonen's message of "Wed, 16 Jun 2010 22:04:16 +0300")
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Cc: Edwin Groothuis <edwin@mavetju.org>,
	FreeBSD Current <freebsd-current@freebsd.org>,
	Xin LI <d@delphij.net>, Gabor Kovesdan <gabor@FreeBSD.org>,
	i18n@FreeBSD.org
Subject: Re: [CFT] BSDL iconv in base system
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Jaakko Heinonen <jh@FreeBSD.org> writes:
> iconv(3) prototype doesn't conform to POSIX.1-2008. Is it a
> well-considered decision?

Probably not, because it breaks the interface.

Imagine that inbuf were just a char *, not a char **.  It would be
perfectly safe to change it to const char *, because you can always
assign a char * to a const char *.

However, inbuf is a char **, which is a pointer to a pointer to char.
Gabor changed it to const char **, which is a pointer to a pointer to
const char.  Unfortunately, the two types are incompatible.  If foo is a
char *, you can't pass &foo as inbuf.

% cat >/tmp/const.c <<EOF
#include <stdio.h>
void fs(char *s) { puts(++s); }
void gs(const char *s) { puts(++s); }
void fsp(char **sp) { puts(++*sp); }
void gsp(const char **sp) { puts(++*sp); }
int main() { char *s =3D "xyzzy", **sp =3D &s; fs(s); gs(s); fsp(sp); gsp(s=
p); }
EOF
% cc -Wall -Wextra -Werror -std=3Dc99 -o/dev/null /tmp/const.c
cc1: warnings being treated as errors
/tmp/const.c: In function =E2=80=98main=E2=80=99:
/tmp/const.c:6: error: passing argument 1 of =E2=80=98gsp=E2=80=99 from inc=
ompatible pointer type
/tmp/const.c:5: note: expected =E2=80=98const char **=E2=80=99 but argument=
 is of type =E2=80=98char **=E2=80=99

This means you can't, say, read data from a file into a buffer and then
pass that buffer to iconv, because the buffer is not const (otherwise
you couldn't have read data into it).  That seems like a pretty
fundamental flaw.

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no