Qt 出现“undefined reference to `vtable for”原因总结

最新推荐文章于 2024-08-27 19:35:15 发布

MoMo_KUA_1

最新推荐文章于 2024-08-27 19:35:15 发布

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本文详细记录了解决Qt自带Demo中出现的undefined reference to `vtable for错误的方法，并附上代码示例。通过使用moc工具生成对应的moc文件并包含到.cpp文件中，可以有效解决此问题。

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今天写了Qt自带的Demo的一个实例，总是会出现undefined reference to `vtable for的错误，查了一些网上的资料终于知道哪里出错了，自己做个记载，直接放上代码，代码中间注释说明了错误的原因

#include <QtCore>
#include <QtGui>


class Pixmap : public QGraphicsWidget
{
    Q_OBJECT

public:
    Pixmap(const QPixmap &pix, QGraphicsItem *parent = 0)
        : QGraphicsWidget(parent), orig(pix), p(pix)
    {
    }

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)
    {
        painter->drawPixmap(QPointF(), p);
    }

    virtual void mousePressEvent(QGraphicsSceneMouseEvent * )
    {
        emit clicked();
    }

    virtual void setGeometry(const QRectF &rect)
    {
        QGraphicsWidget::setGeometry(rect);

        if (rect.size().width() > orig.size().width())
            p = orig.scaled(rect.size().toSize());
        else
            p = orig;
    }

Q_SIGNALS:
    void clicked();

private:
    QPixmap orig;
    QPixmap p;
};

class GraphicsView : public QGraphicsView
{
    Q_OBJECT
public:
    GraphicsView(QGraphicsScene *scene, QWidget *parent = 0) : QGraphicsView(scene, parent)
    {
    }

    virtual void resizeEvent(QResizeEvent *event)
    {
        fitInView(sceneRect(), Qt::KeepAspectRatio);
    }
};


void createStates(const QObjectList &objects,
                  const QRect &selectedRect, QState *parent)
{
    for (int i = 0; i < objects.size(); ++i) {
        QState *state = new QState(parent);
        state->assignProperty(objects.at(i), "geometry", selectedRect);
        parent->addTransition(objects.at(i), SIGNAL(clicked()), state);
    }
}

void createAnimations(const QObjectList &objects, QStateMachine *machine)
{
    for (int i=0; i<objects.size(); ++i)
        machine->addDefaultAnimation(new QPropertyAnimation(objects.at(i), "geometry"));
}

#include "main.moc"         /*:qmake 不会处理.cpp文件里的Q_OBJECT,
    *所以,如果在.cpp文件中有它的话,
    *也会产生undefined reference to vtable for "xxx::xxx". 
    *这时,需要先用moc xxxx.cpp生成相应的moc文件,再包含到.cpp里面去,
    *才能解决这个问题.
    **/

int main(int argc, char **argv)
{
    Q_INIT_RESOURCE(appchooser);

    QApplication app(argc, argv);

    Pixmap *p1 = new Pixmap(QPixmap(":/digikam.png"));
    Pixmap *p2 = new Pixmap(QPixmap(":/akregator.png"));
    Pixmap *p3 = new Pixmap(QPixmap(":/accessories-dictionary.png"));
    Pixmap *p4 = new Pixmap(QPixmap(":/k3b.png"));

    p1->setObjectName("p1");
    p2->setObjectName("p2");
    p3->setObjectName("p3");
    p4->setObjectName("p4");

    p1->setGeometry(QRectF(  0.0,   0.0, 64.0, 64.0));
    p2->setGeometry(QRectF(236.0,   0.0, 64.0, 64.0));
    p3->setGeometry(QRectF(236.0, 236.0, 64.0, 64.0));
    p4->setGeometry(QRectF(  0.0, 236.0, 64.0, 64.0));

    QGraphicsScene scene(0, 0, 300, 300);
    scene.setBackgroundBrush(Qt::white);
    scene.addItem(p1);
    scene.addItem(p2);
    scene.addItem(p3);
    scene.addItem(p4);

    GraphicsView window(&scene);
    window.setFrameStyle(0);
    window.setAlignment(Qt::AlignLeft | Qt::AlignTop);
    window.setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    window.setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);

    QStateMachine machine;
    machine.setGlobalRestorePolicy(QStateMachine::RestoreProperties);

    QState *group = new QState(&machine);
    group->setObjectName("group");

    QRect selectedRect(86, 86, 128, 128);

    QState *idleState = new QState(group);
    group->setInitialState(idleState);

    QObjectList objects;
    objects << p1 << p2 << p3 << p4;
    createStates(objects, selectedRect, group);
    createAnimations(objects, &machine);

    machine.setInitialState(group);
    machine.start();

#if defined(Q_WS_S60) || defined(Q_WS_MAEMO_5)
    window.showMaximized();
#else
    window.resize(300, 300);
    window.show();
#endif

    return app.exec();
}

注意 #include “main.moc" 是因为这是main.cpp 所以生成的是main.moc ， #include"main.moc” 一定要写在后面，也可以写在最后的位置，不能写在开始位置，