Why this error?

[killrazor]

Hi,
I'm trying to compile this code

#include <QApplication>
#include <QLCDNumber>
#include <QPushButton>
#include <QVBoxLayout>
#include <QWidget>
 
class LCDCounter : public QLCDNumber{
	Q_OBJECT
 
private:
		int counter;
public:
	LCDCounter(QWidget *parent = 0);
public slots:
	void increase(void);
 
};
 
LCDCounter::LCDCounter(QWidget *parent)
: QLCDNumber(parent)
{
	counter = 0;
	setSegmentStyle(QLCDNumber::Filled);
	display(0);
}
 
void LCDCounter::increase(){
	display(counter++);
}
 
class MyWidget : public QWidget
 {
	QPushButton *clickMe;
	LCDCounter *counter;
 
 public:
     MyWidget(QWidget *parent = 0);
 };
 
 MyWidget::MyWidget(QWidget *parent)
     : QWidget(parent)
 {
	 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);
 
 }
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	MyWidget w;
	w.show();
	return a.exec();
}

#include <QApplication>
#include <QLCDNumber>
#include <QPushButton>
#include <QVBoxLayout>
#include <QWidget>

class LCDCounter : public QLCDNumber{
	Q_OBJECT

private:
		int counter;
public:
	LCDCounter(QWidget *parent = 0);
public slots:
	void increase(void);

};

LCDCounter::LCDCounter(QWidget *parent)
: QLCDNumber(parent)
{
	counter = 0;
	setSegmentStyle(QLCDNumber::Filled);
	display(0);
}

void LCDCounter::increase(){
	display(counter++);
}

class MyWidget : public QWidget
 {
	QPushButton *clickMe;
	LCDCounter *counter;

 public:
     MyWidget(QWidget *parent = 0);
 };

 MyWidget::MyWidget(QWidget *parent)
     : QWidget(parent)
 {
	 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);

 }

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

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But this error is returned.

1>main.obj : error LNK2001: sÃ*mbolo externo "public: virtual struct QMetaObject const * __thiscall LCDCounter::metaObject(void)const " (?metaObject@LCDCounter@@UBEPBUQMetaObject@@XZ) unresolved
1>main.obj : error LNK2001: sÃ*mbolo externo "public: virtual void * __thiscall LCDCounter::qt_metacast(char const *)" (?qt_metacast@LCDCounter@@UAEPAXPBD@Z) unresolved
1>main.obj : error LNK2001: sÃ*mbolo externo "public: virtual int __thiscall LCDCounter::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@LCDCounter@@UAEHW4Call@QMetaObject@@HPAPAX@Z) unresolved
1>C:\Users\ferran\directo\QT_Tutorials\Debug\Tutorial02.exe : fatal error LNK1120: 3 externos sin resolver

1>main.obj : error LNK2001: sÃ*mbolo externo "public: virtual struct QMetaObject const * __thiscall LCDCounter::metaObject(void)const " (?metaObject@LCDCounter@@UBEPBUQMetaObject@@XZ) unresolved
1>main.obj : error LNK2001: sÃ*mbolo externo "public: virtual void * __thiscall LCDCounter::qt_metacast(char const *)" (?qt_metacast@LCDCounter@@UAEPAXPBD@Z) unresolved
1>main.obj : error LNK2001: sÃ*mbolo externo "public: virtual int __thiscall LCDCounter::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@LCDCounter@@UAEHW4Call@QMetaObject@@HPAPAX@Z) unresolved
1>C:\Users\ferran\directo\QT_Tutorials\Debug\Tutorial02.exe : fatal error LNK1120: 3 externos sin resolver

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How do I guess the method that fails? What are happening?

Many thanks in advance.

[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 ...