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[SOLVED] Running Qt dependent 3rd party dll in Qt dependent host application

  • Hello,
    we are having a problem running our Qt based VST plugin in a host application also based on Qt on Windows platform. Both are linked dynamically, the plugin uses Qt 4.8.5, the host app uses Qt 5.3.1. When I open the plugin in our host app, it starts but the GUI misses graphics - there are no bitmaps or controls, just few green rectangles instead of controls.

    Could anybody recommend any solution? I am not sure if this could be similar to this post - .

    Thanks for any hint.

  • Lifetime Qt Champion


    IIRC your problem is a double set of Qt libraries in the same namespace. I'd rebuild your Qt 4 with a namespace to ensure it doesn't live in the same namespace as the application Qt

  • Thank you for your reply. I have tried to rebuild Qt 5.3.1 in a new namespace and the VST plugin that is using Qt4.8 was left without any changes. So now both Qt versions live in different namespace. Unfortunately, it has not solved the problem.

  • Lifetime Qt Champion

    I'm not sure I'm following you correctly. You can also build the host application ?

  • Finally the problem was not in different Qt versions, but the main reason why there was no graphic in GUI was that QCoreApplication of the VST modul and widgets of GUI were created in a different thread.
    Anyway, the different namespaces of Qt versions will prevent against some eventual future conflicts.

    Thank you for the reply.

  • Lifetime Qt Champion

    You're welcome !

    But there's something still strange here, why QCoreApplication ? It's not meant for GUI application

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