UDP broadcast under C/C++

[bainesy]

Hello again people. Hopefully somebody will be able to help me out with this problem too!!

I need to implement a way of utuilising UDP broadcast in my clinet/server model. More specifically, the client needs to broadcast when it first runs, searching for a server. The server then needs to send a message back with its IP and port number, at which point the TCP connection can be established.

I have the TCP part in my work already - it is fixed within the client and the server, so I always know where to connect to.

What I need now is help on using the UDP broadcast. To be perfectly honest, I have no idea how to use UDP. My google searches always turn up inaccurate results - using it in linux, Java etc etc.

If anybody can provide me with a C/C++ link for some decent tutorials, or indeed help me solve the problem, I'd be very grateful.

Thanks all.

[sunburnt]

As far as I know, sending and receiving a UDP packet uses the same functions as a TCP session, with a few exceptions:

1. You don't need to use listen() or accept() with a UDP socket, since there is no "connection" to speak of. You do use bind() to bind the socket to a port.
2. You use recvfrom() instead of recv() to receive a packet from the specified address. The address you pass in can have ADDR_ANY to receive from any sender.
3. you need to change your call to socket() when creating the socket to pass SOCK_DGRAM instead of SOCK_STREAM, and IPPROTO_UDP instead of IPPROTO_TCP.


I found these snippets, which might help you:
http://www.cs.rpi.edu/courses/syspro...s/server_udp.c
http://www.cs.rpi.edu/courses/syspro...s/client_udp.c

Good luck!

Edit: the sites I posted above are written to be compiled on a *nix platform, but there should be minor differences (if any) to compile them on windows -- simply include the winsock2 header instead of the net/* headers, etc.