website/content/blog/qtcpsocket.md

title	date	draft	tags
QTcpSocket	2020-03-20T16:21:07-04:00	false	C++ Qt

There are two ways that I can think of for checking if a TCP socket times out in Qt. You can either use waitForConnected or a QTimer. The Qt 5.14 documentation noted that the waitForConnected call may randomly fail in Windows.

Here is some shared code for both examples

QTcpSocket *socket = new QTcpSocket(this);
quint16 listenPort = 4444;
int timeout = 1000; // Units: milliseconds
QHostAddress destination("192.168.0.2");

waitForDisconnected

Let's say that we have a QTcpScoket pointer named socket.

socket->connectToHost(destination, listenPort);
if (!socket->waitForConnected(timeout)) {
    qDebug("Connection Timed Out.");
}

Notes:

• waitForConnected is a blocking call
• This does not account for the host lookup call.

QTimer

This method requires a little more setup. Let's assume we have a class named Test that inherits QObject.

// ....
socket->connectToHost(destination, listenPort);
timeoutTimer = new QTimer(this);
timeoutTimer->setInterval(timeout);
timeoutTimer->setSingleShot(true);
connect(timeoutTimer, &QTimer::timeout, this, &Test::timeout);
timeoutTimer->start();
// ....

void Test::timeout(void) {
    qDebug("Connected Timed Out.");
    socket->disconnectFromHost();
}

Notes:

• This method acts asynchronously

In order for the the timeout function to not always hit, we need to make sure we stop the timer when data is received or a TCP error occurs

timeoutTimer->stop();