Question

All 🙂

I have some piece of code with correctly works on Linux and WinXP

int FlowTestIP::do_recvfrom()
{
    int ret;
    struct timeval timeout;// = {2, 0};
    timeout.tv_sec = 2;
    timeout.tv_usec = 0;

    fd_set rfds;
    while(running) {
            FD_ZERO(&rfds);
            FD_SET(m_socket, &rfds);
            ret = select(m_socket + 1, &rfds, 0, 0, &timeout);
            cout << "// select ret = " << ret << " (errno = " << errno << ")" << endl;
            if (ret == -1 || ret == 0) {
                    if (!(ret == 0 && errno == 0))
                            cout << "select ret = " << ret << " (errno = " << errno << ")" << endl;
                    return ret;
            }
            if (FD_ISSET(m_socket, &rfds)) {
                    cout << WSAGetLastError() << endl;
                    break;
            }
    }
    return recvfrom(m_socket, in_buf, mtu, 0, (struct sockaddr *)&si_other, (socklen_t *)&otherAddrSize);
}

But in Windows 7 in continues to loop even when client apptication is exited.
Bad output is

…
// select ret = 1 (errno = 0)
0
// select ret = 1 (errno = 0)
0
// select ret = 1 (errno = 0)
0
FTControlServerThread::run
FTControlServerThread::recieved
pkt->ft_tos = UCHAR_MAX
QFuture::waitForFinished()
client alive true
// select ret = 1 (errno = 0)
0
// select ret = 1 (errno = 0)
0
// select ret = 1 (errno = 0)
0

normaly (on WinXP and Linux) output will be

…
// select ret = 1 (errno = 0)
0
// select ret = 1 (errno = 0)
0
// select ret = 1 (errno = 0)
0
FTControlServerThread::run
FTControlServerThread::recieved
pkt->ft_tos = UCHAR_MAX
QFuture::waitForFinished()
client alive true
QFuture::finished

And that is what I am waiting from it.

Has anyone encountered with such a misbehaviour?

Thanks in advance!

P.S. As @JoachimPileborg asked to show how I call this function:

FlowTest::recv(char *payload, size_t size)  
{  
...  
    while (running) {  
        len = do_recvfrom(); // it virtual method of class FlowTest  
        if (len == -1 || len == 0) {  
            return len;  
        }  

        if (running && !transport_recv_helper()) {  
            continue;  
        } else {  
            break;  
        }  
    }  
...  
}  

and recv is called from server GUI

void FlowTestServer::runTest(FlowTestServerHelper handler)
{
...
        if ((ret = server->recv(rcvdData, (size_t *)&size)) == -1 || ret == 0 || size == 0) {
            if (server_busy == 0)
                break;
            cout << "can't receive data (size == " << size << "; ret = " << ret << ")" << endl;
            continue;
        }
...
}

Answer 1

Firstly: Using cout is allowed to reset errno. It doesn’t usually, but it can, especially on first use when it has to set up the locale. You need to save the value of errno in a temp variable, or use fprintf and friends – as a C lib function POSIX controls its behavior.

Secondly: In Windows, you need to use WSAGetLastError() not errno.

I suggest you make a macro sock_errno which will be (errno) on Linux/unix, and (WSAGetLastError()) on Windows. That will enable to you to code in a platform independent manner.

• See here for more: http://msdn.microsoft.com/en-us/library/windows/desktop/ms737828(v=vs.85).aspx