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Strange problem of the QgsApplication class instead of the QApplication



  • Now I develop an application that based on the "Quantum GIS":http://qgis.org/ libraries. I begin with very simple program:

    @// QGIS Includes
    //
    #include <qgsapplication.h>
    #include <qgsproviderregistry.h>
    #include <qgssinglesymbolrenderer.h>
    #include <qgsmaplayerregistry.h>
    #include <qgsvectorlayer.h>
    #include <qgsmapcanvas.h>
    //
    // Qt Includes
    //
    #include <QString>
    #include <QApplication>
    #include <QWidget>

    int main(int argc, char *argv[])
    {
    QgsApplication app(argc, argv, true);
    return app.exec();
    }
    @
    Okay, when I build this console application and start it under command line of the Quantum GIS shell ("OSGeo4W":http://trac.osgeo.org/osgeo4w/), it fails with a strange message "QApplication::exec: Please instantiate the QApplication object first"; if I exchange a "QgsApplication":http://doc.qgis.org/stable/classQgsApplication.html to a QApplication class, the program start without an error. But the QgsApplication is a child of a QApplication class, as described in the Quantum GIS documentation. What's wrong, I'm confused!


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