select() returns -1 while reading from socket - c++

Question

I'm trying to solve reading from socket timeout problem using select(). Unfortunately this function returns -1 immediatly after getting called. What might be wrong?
commStatus communicate( const char * tx, char * rx, const int bufSize , const char * inetAddr, const int port )
{
commStatus r;
if (!sockInitialised) initSock();
if (sockInitialised)
{
SOCKET s;
struct sockaddr_in server;
server.sin_addr.s_addr = inet_addr(inetAddr);
server.sin_family = AF_INET;
server.sin_port = htons( port );
if((s = socket(AF_INET , SOCK_STREAM , 0 )) == INVALID_SOCKET)
{
std:stringstream d; d <<"Could not create socket : " << WSAGetLastError();
LogIt(d,Level::Error);
} else
{
if (connect(s , (struct sockaddr *)&server , sizeof(server)) < 0)
{
puts("connect error");
r= commStatus::COMM_NO_TRANSMIT ;
} else
{
int l =strlen(tx)+strlen("DATA ");
char* dtx ;
dtx = (char*) calloc(sizeof(char),strlen(tx)+strlen("DATA ") + 1 );
sprintf(dtx,"DATA %s",tx);
if( send(s , dtx , strlen(dtx) , 0) < 0)
{
puts("Send failed");
r= commStatus::COMM_NO_TRANSMIT;
} else
{
int recv_size = 0;
struct timeval selTimeout;
selTimeout.tv_sec = 20; /* timeout (secs.) */
selTimeout.tv_usec = 0; /* 0 microseconds */
fd_set readSet;
FD_ZERO(&readSet);
#define STDIN_FILENO 0
FD_SET(STDIN_FILENO, &readSet);//stdin manually trigger reading
FD_SET(s, &readSet);//tcp socket
int numReady = select(s+1, &readSet, NULL, NULL, &selTimeout);
if(numReady > 0)
{
if((recv_size = recv(s , rx , bufSize ,0)) == SOCKET_ERROR)
{
r= commStatus::COMM_NO_RECEIVE;
} else
{
rx[recv_size] = '\0';
r= commStatus::COMM_OK;
}
} else r=commStatus::COMM_NO_RECEIVE;
}
free(dtx);
}
}
} else r= commStatus::COMM_NO_TRANSMIT;
return r;
}

Answer 1

As far as I can tell, you're trying to pass stdin to Winsock's select() function.
Unfortunately, under Windows, select() only takes socket handles, not generic file descriptors.
If you were to call WSAGetLastError(), you'd probably see that it returns WSAENOTSOCK.

Answer 2

Under C, you can examine the errno variable, it should tell you the specific problem that caused your error.
Alternatively, you may have the perror() function which will give you a readable version:
#include <stdio.h>
:
perror ("select");
If you're under Windows, WSAGetLastError() will serve as the errno variable, with this page giving the possibilities and explanations:
WSANOTINITIALISED - A successful WSAStartup call must occur before using this function.
WSAEFAULT - The Windows Sockets implementation was unable to allocate needed resources for its internal operations, or the readfds, writefds, exceptfds, or timeval parameters are not part of the user address space.
WSAENETDOWN - The network subsystem has failed.
WSAEINVAL - The time-out value is not valid, or all three descriptor parameters were null.
WSAEINTR - A blocking Windows Socket 1.1 call was canceled through WSACancelBlockingCall.
WSAEINPROGRESS - A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSAENOTSOCK - One of the descriptor sets contains an entry that is not a socket.