Signal & Slots problems

Boris1

When I run my program, which include one class declared in header-file and initialized in source-file, my compiler send me these messages:

1)main.obj:-1: ошибка: LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __cdecl Counter::metaObject(void)const " (?metaObject@Counter@@UEBAPEBUQMetaObject@@XZ)
2)main.obj:-1: ошибка: LNK2001: unresolved external symbol "public: virtual void * __cdecl Counter::qt_metacast(char const *)" (?qt_metacast@Counter@@UEAAPEAXPEBD@Z)
3)main.obj:-1: ошибка: LNK2001: unresolved external symbol "public: virtual int __cdecl Counter::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@Counter@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z)

my program(n=main-file is not finished):
main:

#include<QtWidgets>
#include<QObject>
#include<counter.h>

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    QLabel lbl("0");
    QPushButton cmd("ADD");
    Counter counter;
    lbl.show();
    cmd.show();
    app.exec();
}

counter.h:

#pragma once
#include<QObject>
class Counter : public QObject
{
    Q_OBJECT
private:
    int value;
public:
    Counter();
public slots:
    void slotInc();
signals:
    void goodbye();
    void counterchange(int);
};

counter.cpp:

#include "counter.h"


Counter::Counter() : QObject(), value(0)
{}
void Counter::slotInc()
{
    emit counterchange(++value);
    if(value==5)
    {
        emit goodbye();
    }
}

What's wrong?

[Added code formatting tags ~kshegunov]

MSimpson

QWidget derived objects must be heap based. Start by changing your QLabel and QPushButton to pointers. You might start with the sample hello world example.

kshegunov

@Boris1 ,
Hello,
Rerun qmake, the linker errors you see one usually gets when the Q_OBJECT macro hasn't been processed.

Kind regards.

kshegunov

@MSimpson
Hello,

QWidget derived objects must be heap based.

No, they don't have to. I was tempted to write "mustn't", but well that would be just as wrong as saying they "must" be allocated on the heap.

Cheers!

Boris1

@kshegunov
What does mean phrase "rerun qmake"?

mrjj

@Boris1
It means to go to the Build menu and select "Run qmake"
so it runs that tool.

Boris1

Yeah, it works! Thank you all!