help! problem about the select function.

[_J@e_]

hi, guys,

In my current Winsock-based TCP program, on the client side, after I send my request data packet to the Server side using the send socket function, I attempt to get the socket status to see if it has something to read using the select function, and the select function always return 0 meaning the time limit expired on some users' computers, but it's just fine on another users' computers.

Why? Does anybody can tell me why and how to fix it? Thanks!

[j0nas]

Is it select() on the client side that doesn't work?

Have you issued a (non-blocking) recv() before calling select()? What timeout value do you have for the select call? Maybe you can show us some of the code that doesn't work.

[_J@e_]

well, here's the code...

//...
SOCKET sckClient = socket(AF_INET, SOCK_STREAM, 0);

int nOne = 1;
setsockopt(sckClient, IPPROTO_TCP, TCP_NODELAY, (char *)&nOne, sizeof(int)); // just_say_no

struct sockaddr_in addr_to = { 0 };
//...
connect(sckClient, (struct sockaddr *)&addr_to, sizeof(addr_to));

char *buf;
//...
send(sckClient, (const char *)((char*)buf), nDataToSend, 0);

int nRetCode = ::select((int)sckClient + 1, &fdsRead, NULL, NULL, &tvTimeOut);
if (nRetCode==0 )
{ //ERROR: the time limit expired
//Here's the problem! some computers meet the error, but some don't! WHY???
}

recv(sckClient,(char *)buf,nDataToRead, 0);

//...

[j0nas]

How did you initialize fdsRead and tvTimeOut?

I hope you did something like this:tvTimeOut.tv_sec = 30;
tvTimeOut.tv_usec = 0;
FD_ZERO(&fdsRead);
FD_SET(sckClient, &fdsRead);
Currently (at least in the code that you posted), you don't check for SOCKET_ERROR and if the read set is true. I would do something like this:if (nRetCode == 0)
; // got timeout
else if (nRetCode == SOCKET_ERROR)
; // some socket error, call WSAGetLastError() to get a specific error
else {
if (FD_ISSET(sckClient, &fdsRead)) {
; // data ready to be received
}
}