Select function in non blocking sockets - c++

Question

I'm building an online game client and when I try to connect to an offline server, my client freezes so I wanted to use non blocking sockets which suits games since there are other tasks need to be done while connecting to the server.
While using non blocking sockets, the connect function always returns the same value regardless of the result, so people here recommended using the select function to find the result of the connection request.
(setting the non blocking socket before connection)
u_long iMode=1;
ioctlsocket(hSocket,FIONBIO,&iMode);
(setting the sockets sets)
FD_ZERO(&Write);
FD_ZERO(&Err);
FD_SET(hSocket, &Write);
FD_SET(hSocket, &Err);
TIMEVAL Timeout;
int TimeoutSec = 10; // timeout after 10 seconds
Timeout.tv_sec = TimeoutSec;
Timeout.tv_usec = 0;
int iResult = select(0, //ignored
NULL, //read
&(client.Write), //Write Check
&(client.Err), //Error Check
&Timeout);
if(iResult)
{
}
else
{
message_login("Error","Can't connect to the server");
}
The select function always returns -1, why?

Answer 1

When select() returns -1 (SOCKET_ERROR), use WSAGetLastError() to find out why it failed.
If the socket is in the Err set when select() exits, use getsockopt(SOL_SOCKET, SO_ERROR) to retrieve the socket error code that tells you why connect() failed.
if(iResult) evaluates as true for any non-zero value, including -1. You need to use if(iResult > 0) instead, as iResult will report the number of sockets that are signaled in any fd_set, 0 on timeout, and -1 on failure.
Try something more like this instead:
u_long iMode = 1;
if (ioctlsocket(hSocket, FIONBIO, &iMode) == SOCKET_ERROR)
{
int errCode = WSAGetLastError();
// use errCode as needed...
message_login("Error", "Can't set socket to non-blocking, error: ..."); // however you supply a variable value to your message...
}
if (connect(client.hSocket, ...) == SOCKET_ERROR)
{
int errCode = WSAGetLastError();
if (errCode != WSAEWOULDBLOCK)
{
// use errCode as needed...
message_login("Error", "Can't connect to the server, error: ..."); // however you supply a variable value...
}
else
{
// only in this condition can you now use select() to wait for connect() to finish...
}
}
TIMEVAL Timeout;
int TimeoutSec = 10; // timeout after 10 seconds
Timeout.tv_sec = TimeoutSec;
Timeout.tv_usec = 0;
int iResult = select(0, //ignored
NULL, //read
&(client.Write), //Write Check
&(client.Err), //Error Check
&Timeout);
if (iResult > 0)
{
if (FD_ISSET(client.hSocket, &(client.Err)))
{
DWORD errCode = 0;
int len = sizeof(errCode);
if (getsockopt(client.hSocket, SOL_SOCKET, SO_ERROR, (char*)&errCode, &len) == 0)
{
// use errCode as needed...
message_login("Error", "Can't connect to the server, error: ..."); // however you supply a variable value to your message...
}
else
message_login("Error", "Can't connect to the server, unknown reason");
}
else
message_login("Success", "Connected to the server");
}
else if (iResult == 0)
{
message_login("Error", "Timeout connecting to the server");
}
else
{
int errCode = WSAGetLastError();
// use errCode as needed...
message_login("Error", "Can't connect to the server, error: ..."); // however you supply a variable value to your message...
}