Problems with UDP sockets

hi,

It's the first time I use UDP socket so my questions might seem very basic...

I'm building a client server application using UDP protocols...


can anyone explain to me the recvfrom() function works? for example the first parameter is the client socket but how do I initialize the client socket since there is no accept() in UDP??

Useful Links And Good Books
I think it's socket() / bind() / recvfrom()

another question...

something really wierd is happeneing to my UDP server...I just can't open a socket...the socket descriptor keeps getting a negative value...

the funny thing is that the socket I opened in the client application works perfectly...

does this has something to do with the OS?? I'm using WIndows...

You might want to post some of your code, especially the initialization.

Are you writing with MFC or straight win32? If MFC are you using CAsyncSockets? Furthermore are you wanting blocking or non-blocking sockets? All these sort of things would be helpful (well to me at least).

Have you bound the socket to a port yet?

> the socket descriptor keeps getting a negative value
Which means there is an error.
What error checking code have you put in, and what is it telling you?

ok here's one part of my code...

Code:

int main(int argc, char **argv)
{
	int sock;
	int port, queryCode, length;
	int clientSock;
	char message[260];
	struct sockaddr_in servSock_in;
	struct sockaddr_in client_in;
	char *serverIP;			//the IP of the FTP server
	char *hostname;
	
	
	debug = 0;  //debug is OFF by default
	port = 53000; 
	
	if(argc == 2)
	{
		if( strcmp(argv[1], "1") == 0 )
		{
			debug = 1;	//debug mode is ON
			printf("debug mode is ON\n\n");
		}
		
	}

	sock = socket(PF_INET, SOCK_DGRAM,0);   //the dns server socket

	if ( sock< 0)
	{
		printf("I am too tired... I failed to open gate...\n");
		return -1;
	}
	
	memset((char *)&servSock_in,0,sizeof(servSock_in));
	servSock_in.sin_family = PF_INET;
	servSock_in.sin_addr.s_addr = htonl(INADDR_ANY);
	servSock_in.sin_port = htons((u_short)port);


	//bind server
	if (bind(sock, (struct sockaddr *)&servSock_in, sizeof(servSock_in)) < 0)
	{
		printf("I couldn't attach gate to port...\n");
		return -1;
	}
	else
		printf("Waiting for messages...\n");

you asked me about blocking or non blocking sockets..actually I don't know the difference between them (i'm new in network programming..)

i'm sure that the code is OK but I keep on getting a negative descriptor here:
-> sock = socket(PF_INET, SOCK_DGRAM,0);

I'm using Windows visual C++... I made a link to wsock32.lb....

You have to call WSAStartup() before any other socket calls.

that's right!
I can't believe I forgot to do this!!
thanks a lot

Which, if you'd actually BOTHERED to look at some error information rather than the programming equivalent of *shrug*, you would have found out.

I won't be telling you to check for errors again.