How can i call a my function in a qtslot? - c++

Question

I'm trying to call my function as a function slot in Qt,But i don't know how to go about it.
it seems the following approach is wrong :
Update:
According to an answer i updated my source code,but still something is apparently wrong with it.Trying to compile this snippet of code causes these errors:
C2515:' no appropriate default constructor is available.'
And
C2665: QObject::connect':none of the 3 overloads could convert all the
arguments.'
respectively in Visual studio 2010.
#include <QtGui/QApplication>
#include <QPushButton>
#include <QObject>
#include <QMessageBox>
class myclass;
int main(int argc,char *argv[])
{
QApplication a(argc,argv);
QPushButton btnshowmessage("show");
myclass *my=new myclass();
QObject::connect(&btnshowmessage,SIGNAL(clicked()),my,SLOT(warningmessage()));
btnshowmessage.show();
return a.exec();
}
//////////////////////////////////////////////////////////////////////////
class myclass: public QObject
{
Q_OBJECT
public:myclass(){}
public slots:
void warningmessage()
{
QMessageBox::warning(0,"Warning","Test Message!",QMessageBox::Ok);
}
};

Answer 1

You use signals and slots to connect one Object's signal to another Object's slot. Every signal or slot should be inside a class which must be also derived from QObject class and contain the Q_OBJECT macro.
So to make your code work, put the slot into some class of yours:
class MySlotClass:public QObject
{
Q_OBJECT
public slots:
void MyFunction()
{
QMessageBox::warning(0,"WarningTest","This is a waring text message",QMessageBox::Ok);
}
}
and connect like this:
MySlotClass m = new MySlotClass();
Qobject::connect(&btnShowaMessageBox,SIGNAL(clicked()), &m ,SLOT(MyFunction()));

Answer 2

Currently Qt does not allow connection of signals to functions that are not declared as slots on some QObject derivative. I believe Qt5 may offer this possibility, but connect will have different syntax to allow this.
basically your slot function must be in a QObject derived class and declared in a
public slots:
section.
Read the documentation on signals/slots.