#include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

#include <QGuiApplication>
#include <QQuickView>
int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQuickView *view = new QQuickView;
    view->setResizeMode(QQuickView::SizeRootObjectToView);
    view->setSource(QUrl(QStringLiteral("qrc:/main.qml")));
    view->show();

    return app.exec();
}

 QQuickWidget *view = new QQuickWidget;
 view->setSource(QUrl::fromLocalFile("myqmlfile.qml"));
 view->show();