#include <sys/time.h>
#include <sys/types.h>
#include <string.h>

// This is an example of how 'select' system call works on UNIX.
// The syntax for 'select' on WinSock is the same. The include
// header file has to be changed to
//  #include <process.h>
//  #inlucde <winsock.h>
// The syntax for FD_SET and FD_ISSET is slightly different
// on WinSock. See attached example.
//
// Assume a number of sockets have been opened before, and socket IDs
// are stored in sockId
void Polling(int sockId[], int numSocks)
{
    fd_set   fdvar;
    int      numReady = 0;
    struct timeval timer;
    int      i;

    timer.tv_sec = 3;
    timer.tv_usec = 500;   // the time-out is set to be 3.5 sec.
    
    FD_ZERO(&fdvar);      // initialize fdvar
    for (i = 0; i < numSocks; i ++)
	FD_SET(sockId[i],&fdvar);  // copy values of sockid to fdvar

    // we allow at maximum 16 sockets open simultaneously
    // numReady indicates how many sockets are ready
    numReady = select(16,&fdvar,(fd_set *)0,(fd_set *)0,&timer);
    if (numReady < 0)
	perr("Selection error");
    if (numReady > 0)  // some sockets are ready
    {
	for (i = 0; i < numSocks; i ++)
        // check which one is ready
	if (FD_ISSET(sockId[i],&fdvar) > 0)
	    doWork(sockId[i]);     // process the work on socket sockId[i]
    }
}