How can QML get a 2D double array filled by Q_INVOKABLE C++ member function?

Tom asso

I'm developing with Qt 6.8.2 on ubuntu 22.04.
QML code should call a Q_INVOKABLE member function of a C++ object; the function should return a 1-dimensional double array. Based on advice from Claude.ai I use the following approach, but QML encounters a seg-fault when it attempts to access the returned double array:
C++:

class MyClass : public QObject {
    Q_OBJECT
  public:
    /// Return the x-y-z position
    Q_INVOKABLE QVariantList getLightPosition(void) {
    double position[3] = {1., 2., 3.};
    QVariantList result;
  
    for (int i = 0; i < 3; i++) {
      qDebug() << "getLightPosition(): " << i << ": " << position[i];
      result.append(position[i]);
    }
  }
}

QML:

Dialog {
   [...]
    onOpened: { console.log('settings3dDialog opened');
                // Set values in settings gui to current values
                var pos = topoDataItem.getLightPosition()
		console.log('pos[0]=', pos[0])		
      }
}

How to properly do this?
Thanks!

Jonas Karlsson

It looks like you are missing a "return result" in getLightPosition

Tom asso

@Jonas-Karlsson You are exactly right - thank you!
Why didn't the compiler spot that error??

SGaist

@Tom-asso hi,

Check the build log, you likely have a warning about that issue from the compiler.