IN_MULTICAST

Question

Hi,

In Desktop applications you can use IN_MULTICAST macro defined in winsock.h, with IN_ADDR to determine if an address is a multicast address

bool isMulticast(const IN_ADDR& addr)
{
    return IN_MULTICAST(ntohl(addr.s_addr));
}

How can i do the same in a Metro application? i don't see a way to do the same using Windows::Networking::Hostname.

Any ideas?

Regards,

Jose

Answer 1

I did not find out the  IN_MULTICAST in Winsock.h or Winsock2.h.

Is it in third party library?

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NEU_ShieldEdge

Answer 2

That is not in a third party library, is part of Windows SDK

C:\Program Files\Windows Kits\8.0\Include\shared\ws2def.h included by

C:\Program Files\Windows Kits\8.0\Include\um\WinSock2.h

#define IN_MULTICAST(i)         IN_CLASSD(i)

In previous versions of Winksock.h that definition was there. http://research.microsoft.com/en-us/um/redmond/projects/invisible/include/winsock.h.htm

Answer 3

The Runtime networking stack is moving away from explicit IP address -- for example, your local IP address is considered to be a "HostName", and there aren't any type of IP address classes (e..g, no IN_ADDR or SOCKADDR or anything similar). 

Consequently, we have no equivilent of the IN_MULTICAST macro.

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Network Developer Experience Team (Microsoft)

Answer 4

I see, i my library i have resort to some string comparisons to solve that, it works, but will be easier if WinRT provide some kind of replacement for IN_MULTICAST.

//
// Return true if the hostname represent an IPv multicast
// address.
//
bool isMuticast(HostName^);

In my case that is needed because, when the user enter a multicast address the lib must call JoinMulticastGroup, otherwise it just use ConnectAsync to send data to this UDP endpoint.

For IPv4 i check first octet is between 233 and 239, for IPv6 the address start with FF, http://en.wikipedia.org/wiki/Multicast_address, easy to implement using string comparisons

Thanks for taking the time to look at this.

Regars,

Jose