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Re: IP_MULTICAST_IF et. all / Winsock[2] value conflict
On Thu, 29 Sep 2005, Corinna Vinschen wrote:
> On Sep 29 11:27, Brian Ford wrote:
> > I'm having a problem with IP_MULTICAST_IF not working on Cygwin. While
> > investigating, I came across this MS KB article that might describe my
> > problem:
> >
> > http://support.microsoft.com/default.aspx?scid=kb;en-us;257460
> >
> > IP_MULTICAST_IF can have two values (2 or 9) depending on whether you're
> > linking to Winsock 1 or 2. By preprocessing my source and looking in
> > /usr/include/cygwin/socket.h, I see we are using the value 2 which means
> > it will only work if we link to Winsock 1?
> >
> > IIRC, Cygwin dynamically loads which ever library is present or version 2
> > if both are available? I assume we are loading version 2 on my system
> > given it is WinXP?
> >
> > I don't understand the Cygwin magic to do this well enough to supply a
> > patch. I also don't understand how including Winsock2.h followed by
> > Ws2tcpip.h is supposed to allow you to link against either library.
> >
> > Here's hoping that Corinna or someone else is less confused and can supply
> > a fix to either Cygwin or my limited understanding. Thanks.
>
> There's no easy fix right now. We have to drop all traces of Winsock1
> in Cygwin and change the headers accordingly.
Can't we just translate these based on a flag indicating what version we
dynamically loaded?
> Since you didn't say what problem you had, I assume that IP_MULTICAST_IF
> just didn't do what you wanted.
Correct. It did not send out the interface I requested.
> Did you try to use just the value 9 instead of IP_MULTICAST_IF?
Not yet, but I will this afternoon. Thanks.
--
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained pilot...
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