Recv returns junk

[Ness]

#pragma comment(lib, "winmm.lib")
#pragma comment(lib, "wsock32.lib")

#include <windows.h>
#include <winsock.h>
#include <stdio.h>

int err;

SOCKET Server;
SOCKET Client;

bool IsServer = false;

int startServer();
DWORD WINAPI beginRecieve(LPVOID);

int startServer()
{
	Server = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);

	if(Server == INVALID_SOCKET)
	{
		printf("ERROR: Unable to create server socket.\n");
	}

	SOCKADDR_IN sockIn;

	sockIn.sin_family = AF_INET;
	sockIn.sin_port = htons(4000);
	sockIn.sin_addr.s_addr = inet_addr("127.0.0.1");

	err = bind(Server,(LPSOCKADDR)&sockIn,sizeof(struct sockaddr));

	if(err != 0)
	{
		printf("ERROR: Cannot bind socket to port 4001.\n");
	}

	printf("Waiting for data...\n");

	return 0;
}

int main()
{
	WSADATA wsaData;

	err = WSAStartup(MAKEWORD(1,1),&wsaData);

	if(err != 0)
	{
		printf("ERROR: Unable to initialize Winsock.\n");
	}

	startServer();	

	CreateThread(0,0,&beginRecieve,0,0,0);

	do {} while(true);
}

DWORD WINAPI beginRecieve(LPVOID)
{
	int bytesRecieved;
	const char *buffer;

	while(true)
	{
		bytesRecieved = recv(Server,(char *)buffer,100,0);

		printf(buffer);
	}
}

It prints ☺'s to the console. I made sure nothing was being sent to that particular port, but nothing was.

[Massad]

I think const char *buffer needs to be allocated before you can receive data into it.

I think what's happening is that when you are outputing the value of buffer, it outputs uknown values due to the fact that it does not know where buffer is pointing to in memory since you did not initialize it to a null or with a valid memory location.

Try that, see what happens

[Ness]

Let me throw VirtualAlloc in there....

works perfectly! Thanks so much for reminding me!

buffer = (const char *)VirtualAlloc(0,100,MEM_COMMIT,PAGE_READWRITE);

[Ness]

Though I still have a problem. When I recieve data, I only get three chars, but I set the limit to 100. What can I do there?

[wayside]

Originally posted by Ness
Though I still have a problem. When I recieve data, I only get three chars, but I set the limit to 100. What can I do there?

There may have only been three bytes ready to be read.

YOu may also have a problem with this line:

    do {} while(true);

This puts you into a tight loop which will use 100% of available cpu.

At worst, do this:

    do { Sleep(1000); } while (true);

At best use an event or whatever and do proper synchronization.

[Massad]

yes, there may only be 3 bytes to be read so if your buffer is filled up with junk, it will display the junk.

I like to use memset to clear the buffer before any recv operation when i do socket programing. Try it let us know how it goes

[Andreas Masur]

[Moved thread]

[Ness]

i did the do while loop because I was doing some testing on the recieve function, and I didn't want the console window to close on me.

[Ness]

I tried using memset, it still only returned 3 chars.

[Mathew Joy]

It has been stressed over and over again that you have to checked for the return value for error using GetLastError() to newbies. A few looks in this forum (Networking) would have revealed that. If you had checked then you'd have understood that the socket you are using is not connected. There is no call to accept(). A call to accept() would have revealed that there is no listen(). I suggest you to look at some sample code before you set to write a server. Lots of samples are available on the net.