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Date: Sat, 13 Jun 2009 17:30:32 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] [PATCH] Win32: Don't remove const attribute in type
	casts.
Message-ID: <20090613163032.GD16220@shareable.org>
References: <1244891127-15561-1-git-send-email-weil@mail.berlios.de>
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To: Stefan Weil <weil@mail.berlios.de>
Cc: Blue Swirl <blauwirbel@gmail.com>, QEMU Developers <qemu-devel@nongnu.org>

Stefan Weil wrote:
> Type casts removing the const attribute are bad because
> they hide the fact that the argument remains const.
> 
> They also result in a compiler warning (at least with MS-C).

> -    return sendto(s->fd, (void *)buf, size, 0,
> +    return sendto(s->fd, (const void *)buf, size, 0,
>                    (struct sockaddr *)&s->dgram_dst, sizeof(s->dgram_dst));

1. Why isn't the (struct sockaddr *) const too?

   It is declared like this in at least one Win32 header file:

      WINSOCK_API_LINKAGE int PASCAL sendto(SOCKET, const char*,
                                            int, int,
                                            const struct sockaddr*, int);

   So why does the buffer pointer need to be const, but the sockaddr
   does not, for MS-C to be happy?

2. Possibly just a historical note.  Passing a const pointer will
   produce compiler warnings or even errors on any platform where
   sendto is declared in system headers without const pointer
   arguments.  I think some old unixes did that, but probably QEMU
   isn't targetting any of them.

   However, it might be why the (void *) cast was put there in the
   first place, as there is no need for any cast at all on platforms
   where sendto() is declared the modern way.

3. See 2 - maybe just get rid of the cast?

-- Jamie