Connecting multiple sockets to a server

lockd · #1 12-Aug-2007, 03:36

this is what i tried for 20 sockets

for(int x = 0; x < 20; x++)
{
SOCKET sSocket = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);

what is the correct way?

davekw7x · #2 12-Aug-2007, 10:19

Quote:

Originally Posted by lockd

what is the correct way

The correct way to what?

If you are thinking about a server that can communicate with 20 clients (each with its own socket/port), then I suggest you visit http://beej.us/guide/bgnet

Download the excellent Beej's Guide to Network Programming. A brand-new revision was released a few days ago, but for some years now Beej's Guide has been one of the absolute best jump-starters for beginning to learn sockets programming.

There is a multi-client server example, but I suggest that you not try to skip ahead to its section; work your way through the Guide. Read and try to understand and compile (and execute) all of the examples.

If you run into problems, then show us what you tried and explain what it is that you don't understand about what did or did not happen when you tried your code.

Regards,

Dave

lockd · #3 12-Aug-2007, 17:13

Hi Dave, I have read Beej's guide, it's good but I'm learning Winsock...

Yes he does give a multi-connection server example, but my goal is to connect multiple sockets from a single client to a single server and keep them open...

that's why I looped the socket, but I'm not sure if that is the correct way since I get errors... maybe it's just minor errors I need to fix or maybe the entire looping concept is impossible?

SOCKET sSocket[25];

for(int iCount = 0; iCount < 20; iCount++)
{
sSocket[iCount] = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
}

davekw7x · #4 12-Aug-2007, 20:10

Quote:

Originally Posted by lockd

...I have read Beej's guide...

So, you have a model for a server that can accept connections from any number of clients: A single "listener socket to accept connection requests. And then "accept" to create a new socket for each incoming request. A loop to monitor the "listener" socket and all of the established clients connections.

The whole example in Beej is a little more than 100 lines of "straight" C code. See footnote.

Of course you put into the loop whatever it is that you want to do with the sockets that communicate to the 20 client ports.

If you want to make a single client program that makes multiple socket connections to a server, you can certainly do it in a loop if you want to. For each connection you have a socket fd and a sock_addr_in structure.

If you show us your code and tell us what the errors were (and maybe tell a little about the application), maybe someone can help.

Regards,

Dave

Footnote:
I have run a number of Beej's examples (including selectserver.c) on Windows XP with Borland and Microsoft compilers, but my present platform is Linux. If I can't give you specific Windows answers, maybe someone else can.

lockd · #5 12-Aug-2007, 20:47

Hi, I think I everything should be fine but there are still errors:

CPP / C++ / C Code:

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

using namespace std;

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

#define CS_ERROR 1
#define CS_OK 0

void sError(char*);

int main()
{

	WORD version;
	WSADATA wsaData;
	int rVal=0;

	version = MAKEWORD(2,0);

	WSAStartup(version,(LPWSADATA)&wsaData);
cout<<"Press Enter to continue";
cin.get();
	LPHOSTENT hostEntry;

	//store information about the server
	hostEntry = gethostbyname("127.0.0.1");

	if(!hostEntry)
	{
		sError("Failed gethostbyname()");
		//WSACleanup();
		return CS_ERROR;
	}

	//create the socket and Loop it
	SOCKET theSocket[25];                      //<----

for(int iCount = 0; iCount < 20; iCount++)     //<----
{
theSocket[iCount] = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);  //<---

	SOCKET theSocket = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);  // <---
  
	if(theSocket == SOCKET_ERROR)
	{
		sError("Failed socket()");
		return CS_ERROR;
	}

	//Fill in the sockaddr_in struct
	SOCKADDR_IN serverInfo;

	serverInfo.sin_family = PF_INET;
	serverInfo.sin_addr = *((LPIN_ADDR)*hostEntry->h_addr_list);

	serverInfo.sin_port = htons(80);

	rVal=connect(theSocket,(LPSOCKADDR)&serverInfo, sizeof(serverInfo));
	if(rVal==SOCKET_ERROR)
	{
		sError("Failed connect()");
		return CS_ERROR;
	}
cout<<"Connected";
cin.get();


	closesocket(theSocket);
	cout << "closing client"<< endl;
	WSACleanup();
	
	return CS_OK;
}

void sError(char *str)
{                           //  <---  error starts here  line 79
	MessageBox(NULL, str, "SOCKET ERROR", MB_OK);
	WSACleanup();
}}

The errors include:
In function 'int main()'
79: a function definition is not allowed here before '{' token
79: expected '.' or ';' before '{' token

cable_guy_67 · #6 12-Aug-2007, 21:19

Quote:

Originally Posted by lockd

Hi, I think I everything should be fine but there are still errors:

CPP / C++ / C Code:

// code removed ...

	return CS_OK;
}

void sError(char *str)
{                           //  <---  error starts here  line 79
	MessageBox(NULL, str, "SOCKET ERROR", MB_OK);
	WSACleanup();
}}

The errors include:

Code:

In function 'int main()'
79: a function definition is not allowed here before '{' token
79: expected '.' or ';' before '{' token

The last } actually closes main(). I think you want sError() to be outside of your main, not inside.

Mark

lockd · #7 12-Aug-2007, 21:44

Hi Paul thx for the response, I edited the code too:

CPP / C++ / C Code:

	closesocket(theSocket);
	cout << "closing client"<< endl;
	WSACleanup();
	
	return CS_OK;
}}

void sError(char *str)
{                     
	MessageBox(NULL, str, "SOCKET ERROR", MB_OK);
	WSACleanup();
}

and the result = the error :too many decimal points in number
I'm lost on this

davekw7x · #8 13-Aug-2007, 09:30

Quote:

Originally Posted by lockd

and the result = the error :too many decimal points in number
I'm lost on this

Is this a compiler error? Post the actual code that you are trying to compile.

Note that, regardless of compiler error(s), your code appears to try to make one connection then closes the socket and exits. Huh?

The following makes no sense:

CPP / C++ / C Code:

    SOCKET theSocket[25];
    for (int iCount = 0; iCount < 20; iCount++)
    {
        theSocket[iCount] = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
        SOCKET theSocket = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
.
.  // call connect for theSocket
.
        closesocket(theSocket);
        cout << "closing client" << endl;
        WSACleanup();

        return CS_OK;
    }

Since you said that you wanted 20 sockets open at the same time, wouldn't you need something more like:

CPP / C++ / C Code:

    for (int iCount = 0; iCount < 20; iCount++)
    {
        theSocket[iCount] = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);

.
. // call connect for theSocket[iCount]
.
    }
.
. // do whatever you want with the 20 sockets that are now connected
.
    cout << "closing sockets" << endl;
    for (int i = 0; i < iCount; i++) {
        closesocket(theSocket[iCount]);
    }
    WSACleanup();

Regards,

Dave

lockd · #9 13-Aug-2007, 15:54

I got it to work perfect thx for your replies helped so much

davekw7x · #10 13-Aug-2007, 17:02

Well, I hope you were able to overcome my obviously incorrect closing loop.

Quote:

Originally Posted by davekw7x

CPP / C++ / C Code:

. // do whatever you want with the 20 sockets that are now connected
.
    cout << "closing sockets" << endl;
    for (int i = 0; i < iCount; i++) {
        closesocket(theSocket[iCount]);
    }
    WSACleanup();

That is, I hope that you would have seen that the loop should be more like

CPP / C++ / C Code:

    for (int i = 0; i < 20; i++) {
        closesocket(theSocket[i]);
    }

I regret the error, but I hope the main idea was clear.

Regards,

Dave

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