[Qemu-devel] [PATCH] Win32: Don't remove const attribute in type casts.

[Qemu-devel] [PATCH] Win32: Don't remove const attribute in type casts.

[Stefan Weil]

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).

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
---
 net.c       |    2 +-
 qemu-char.c |    2 +-
 vnc.c       |    2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net.c b/net.c
index 58d68b5..af9de73 100644
--- a/net.c
+++ b/net.c
@@ -1507,7 +1507,7 @@ static ssize_t net_socket_receive_dgram(VLANClientState *vc, const uint8_t *buf,
 {
     NetSocketState *s = vc->opaque;
 
-    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));
 }
 
diff --git a/qemu-char.c b/qemu-char.c
index a63d860..a8afe94 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -1708,7 +1708,7 @@ static int udp_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
 {
     NetCharDriver *s = chr->opaque;
 
-    return sendto(s->fd, (void *)buf, len, 0,
+    return sendto(s->fd, (const void *)buf, len, 0,
                   (struct sockaddr *)&s->daddr, sizeof(struct sockaddr_in));
 }
 
diff --git a/vnc.c b/vnc.c
index 109c2f3..e1ca9f8 100644
--- a/vnc.c
+++ b/vnc.c
@@ -961,7 +961,7 @@ long vnc_client_write_buf(VncState *vs, const uint8_t *data, size_t datalen)
         }
     } else
 #endif /* CONFIG_VNC_TLS */
-        ret = send(vs->csock, (void *)data, datalen, 0);
+        ret = send(vs->csock, (const void *)data, datalen, 0);
     VNC_DEBUG("Wrote wire %p %zd -> %ld\n", data, datalen, ret);
     return vnc_client_io_error(vs, ret, socket_error());
 }
-- 
1.5.6.5

[Qemu-devel] Re: [PATCH] Win32: Don't remove const attribute in type casts.

[Blue Swirl]

On 6/13/09, Stefan Weil <weil@mail.berlios.de> 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).
>
>  Signed-off-by: Stefan Weil <weil@mail.berlios.de>

Thanks, applied.

Re: [Qemu-devel] [PATCH] Win32: Don't remove const attribute in type casts.

[Jamie Lokier]

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

Re: [Qemu-devel] [PATCH] Win32: Don't remove const attribute in type casts.

[Stefan Weil]

Jamie Lokier schrieb:
> 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.

Correct.

>
> 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
>


const was not added to the type cast because the
function prototype allows a const pointer argument.

const was added because the casted value (buf) has this attribute.
&s->dgram_dst is part of s which does not have a const attribute,
so there is no need to add const to that type cast.

Replacing uint8_t * by void * in many QEMU's functions
might be the best solution to get rid of type casts,
but that can only be done by a maintainer (or at least
the maintainers must support such changes).

Regards,
Stefan