Why this error?

[ChrisW67]

QLCDNumber is already a QObject so you don't require the Q_OBJECT macro in your derived class definition. The linker is getting confused looking in the wrong place for the tables used to support QObjects.

[wagmare]

but if he removes Q_OBJECT the connect will be failed ... at console he will receive
Object::connect: No such slot QLCDNumber::increase()

[squidge]

MOC isn't being run. If your using the QtCreator IDE, then use Build->Run QMake. Leave the Q_OBJECT in there, it's required.

[wagmare]

but in normal qt compilation ...

he should include "main.moc" in his main file

code will be

#include <QApplication>
#include <QtGui>
 
class LCDCounter : public QLCDNumber{
        Q_OBJECT
 
private:
        int counter;
public:
        LCDCounter(QWidget *parent = 0)
                :QLCDNumber(parent)
        {
                counter = 0;
                setSegmentStyle(QLCDNumber::Filled);
                display(0);
        }
public slots:
        void increase()
        {
                display(counter++);
 
        }
 
};
class MyWidget : public QWidget
{
        Q_OBJECT
public:
        MyWidget()
                : QWidget(0)
        {
                clickMe = new QPushButton("Click me!");
                counter = new LCDCounter();
                connect(clickMe,SIGNAL(clicked()),counter,SLOT(increase()));
                QVBoxLayout *boxLayout = new QVBoxLayout;
                boxLayout->addWidget(clickMe);
                boxLayout->addWidget(counter);
                setLayout(boxLayout);
 
        }
 
 
private:
        QPushButton *clickMe;
        LCDCounter *counter;
};
 
 
#include "main.moc"
 
int main(int argc, char *argv[])
{
        QApplication a(argc, argv);
        MyWidget w;
        w.show();
return a.exec();
}

#include <QApplication>
#include <QtGui>

class LCDCounter : public QLCDNumber{
        Q_OBJECT

private:
        int counter;
public:
        LCDCounter(QWidget *parent = 0)
                :QLCDNumber(parent)
        {
                counter = 0;
                setSegmentStyle(QLCDNumber::Filled);
                display(0);
        }
public slots:
        void increase()
        {
                display(counter++);

        }

};
class MyWidget : public QWidget
{
        Q_OBJECT
public:
        MyWidget()
                : QWidget(0)
        {
                clickMe = new QPushButton("Click me!");
                counter = new LCDCounter();
                connect(clickMe,SIGNAL(clicked()),counter,SLOT(increase()));
                QVBoxLayout *boxLayout = new QVBoxLayout;
                boxLayout->addWidget(clickMe);
                boxLayout->addWidget(counter);
                setLayout(boxLayout);

        }


private:
        QPushButton *clickMe;
        LCDCounter *counter;
};


#include "main.moc"

int main(int argc, char *argv[])
{
        QApplication a(argc, argv);
        MyWidget w;
        w.show();
return a.exec();
}

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[killrazor]

Hi all and many thanks for your responses.

MOC isn't being run. If your using the QtCreator IDE, then use Build->Run QMake. Leave the Q_OBJECT in there, it's required.

I forgot to say that I'm working with Visual Studio 2008 and QT 4.6.
With the Visual Studio add-in, the project created with the assistant doesn't includes the moc file as wagmare says. I'll try the changes you are suggesting.

Thanks

[wagmare]

include "main.moc" above main and macro Q_OBJECT in MyWidget class .. your code is working fine ...