WinSock At A Glance
(author: bkenwright@xbdev.net)
As far as this document goes, I thought I'd put together a quick read doc,
you can glance through this in a few seconds...and either get a feel for the
Winsock or refresh your memory.
Header File and Import Library
To use any of the WinSock API's, you are required to include the header
file 'winsock2.h' and link the file 'ws2_32.lib' to the final exectuable.
#include <windows.h>
#include <winsock2.h>
WinSock: Initialization
Well before you can use WinSock, you have to initialize it, it can't get
any more simple than this. Simply call WSAStartup to startup the
interface to WinSock.
WSADATA wsa;
WORD version;
int error;
version = MAKEWORD{ 2, 0}; // e.g. 0x02000
error = WSAStartup( version, &wsa );
/* check for error */
if( error != 0 )
{
/* error occured */
return false;
}
/* check for the correct version */
if( LOBYTE( wsa.wVersion ) != 2 ||
HIBYTE( wsa.wVersion ) != 0 )
{
/* incorrect WinSock version */
WSACleanup();
return false;
}
/* WinSock has been initialized */
Server: Create Socket
SOCKET server;
server = socket ( AF_INET, SOCKET_STREAM, 0 );
Server: Starting Server
struct sockaddr_in sin;
memset( &sin, 0, sizeof(sin) );
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = INADDR_ANY;
sin.sin_port = htons( 21 );
if ( bind( server, &sin, sizeof(sin) = = SOCKET_ERROR
)
{
/* could not start server */
return false;
}
Server: Listen for Client
while( listen( server, SOMAXCONN ) = =
SOCK_ERROR );
SOMAXCONN (#defined as 5) - is the backlog, so if you set this to 1,
instead of saying SOMAXCONN, you can only have one connection, and the other
connections are just ignored. SOMAXCONN let the system decide the
maximum number.
Server: Accepting Connection
SOCKET client;
int length;
length = sizeof( sin );
client = accept( server, &sin, &length );
Client: Create Socket
SOCKET client;
client = socket ( AF_INET, SOCK_STREAM, 0 );
Client: Get Host
Well as a client, for example a web browser, we dont' remember IP's what we
do remember is host address'es....for example,
www.xbdev.com now using this URL we can get our IP number. We
do this magic, by using the function gethostbyname
struct hostent host;
host = gethostbyname ( "www.xbdev.net"
);
Client: Connecting to Server
struct sockaddr_in sin;
memset( &sin, 0, sizeof(sin) );
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = ((struct in_addr* ) (host->h_addr))
->s_addr;
sin.sin_port = htons( 21 );
if ( connect( client, &sin sizeof(sin) ) = =
SOCKET_ERROR ) // SOCKET_ERROR defined as -1
{
/* could not connect to server */
return false;
}
Send and Receive Data
Once you've connected your sockets...its just a matter of sending the
data...think of it as connecting a tube between two points. Once you've
connected them, you can push water down your tube...hehe...I mean send data.
The functions for sending and receiving data are 'send'
and 'recv'
int send( SOCKET s, const char FAR *buf, int len, 0
);
int recv( SOCKET s, char FAR *buf, int len, 0 );
e.g.
char buf[10] = "test";
send( client, buf, strlen(buf), 0 );
Closing Socket
When we are finished with a socket, we can close it simply by calling the
fucntion closesocket. Easy ;)
closesocket( server );
WinSock: Shutdown
Once finished with the WinSock system, we need to shut it down by calling
the function WSACleanup.
WSACleanup();
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