How to set up a Winsock UDP socket?

Question

I want to create a Winsock UDP socket that only sends data to a client. I want the kernel to choose an available port for me. On the other hand, I want to indicate which local IP to use, since I'm running a few nics.

I've tried combing through the maze of socket options, as well as binding with the port in the socket address set to 0 to no avail.

My code is in Win32 C++.

Answer 1

On http://www.linuxhowtos.org/C_C++/socket.htm search for "Alternative types of sockets "

BTW, this was the second item found in a google search for "c++ sockets". The winsock portion of this is left for the OP

Answer 2

Not a direct "HowTo", but I have been using an open source library called "ACE (Adaptive Communication Environment" for all my TCP and UDP socket programming and found it very useful and powerful. It takes a "software pattens" approach to providing building blocks to solve your particular problem. I was able to use their UDP encapsulation to connect to a given port and have replies sent to a free port chosen by the system. Alternatively you can specify the return port if you wish. ACE is available here: ACE Homepage

Answer 3

Please excuse the lack of error checking:

char pkt[...];
size_t pkt_length = ...;
sockaddr_in dest;
sockaddr_in local;
WSAData data;
WSAStartup( MAKEWORD( 2, 2 ), &data );

local.sin_family = AF_INET;
local.sin_addr.s_addr = inet_addr( <source IP address> );
local.sin_port = 0; // choose any

dest.sin_family = AF_INET;
dest.sin_addr.s_addr = inet_addr( <destination IP address> );
dest.sin_port = htons( <destination port number> );

// create the socket
SOCKET s = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
// bind to the local address
bind( s, (sockaddr *)&local, sizeof(local) );
// send the pkt
int ret = sendto( s, pkt, pkt_length, 0, (sockaddr *)&dest, sizeof(dest) );

Answer 4

When you say "I want to indicate which local IP to use, since I'm running a few nics", do you mean that you want to specify the ip address, or do you want to specify the nic and use the associated ip address?

If you are trying to specify the nic, this question should be relevant.