Debugging

Sending output to the device log

Besides running the debugger there are some other ways that you can debug your Cascades application. In JavaScript, you can use the console.log() function to output text and variables to the slogger2.log. You can now view all slogger2.log information in the Device Log view in the QNX Momentics IDE. To open the Device Log view, on the Window menu, click Show View > Other. Expand Debug and select Device Log.

For example, within the CircularSlider application, we capture the valueChanged() signal and output the slider value to the slogger2.log when the value changes:

CircularSlider {
    layoutProperties: DockLayoutProperties {
        horizontalAlignment: HorizontalAlignment.Center
        verticalAlignment: VerticalAlignment.Center
    }
    onValueChanged: {
        console.log("Slider value: " + value);
    }
}

Using qDebug()

In C++, a common way to output text and variables to the slogger2.log is by using qDebug(). Here's an example of how QCompass readings are displayed:

 QCompassReading *reading = m_CompassSensor->reading(); 

qreal azimuth = reading->azimuth();
qDebug() << "The azimuth is " << azimuth << " degrees."; 

To see debug information that is output from qDebug(), you can access the slogger2 logs directly as follows:

1. In the QNX Momentics IDE, in the Target Navigator view, right-click the device target. Click Launch SSH Session.
2. In the terminal that appears, do one of the following:
   1. To view the current slogger2 logs, type slog2info.
   2. To view real-time output for the processes that are being debugged (for applications that are running in development mode), type slog2info -w.
   3. To view help information on slogger2, type slog2info -h.

You can also access the log files directly in the /tmp/slogger22 on the device and run these logs through slog2info at a later time.

Using fprintf() to send output directly to the console

You can use the fprintf() function with stdout or stderr as the output stream to receive output directly to the console. Or, you can use a function similar to the following:

void myMessageOutput(QtMsgType type, const char* msg){
                fprintf(stdout, "%s\n", msg);                
                fflush(stdout); 
} 

Then, you can register this handler function with qDebug by calling the qInstallMsgHandler() function in your main function after the default Application creation, similar to the following:

int main(int argc, char **argv)
{
    Application app(argc, argv);
    qInstallMsgHandler(myMessageOutput);
    ...
}

After this, qDebug() calls will be logged to the console.