signal & slot problem

[ahmetturan]

i created one pushbutton and label in myClass.cpp;

QLabel *lbl=new QLabel();
QPushButton *btn=new QPushButton("button");
 
ui->tableWidget->setCellWidget(0,0,lbl);
ui->tableWidget->setCellWidget(0,1,btn);

QLabel *lbl=new QLabel();
QPushButton *btn=new QPushButton("button");

ui->tableWidget->setCellWidget(0,0,lbl);
ui->tableWidget->setCellWidget(0,1,btn);

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i want that: when i click button, calendar will open and when i click calendar, date will be written on label.
and i want to use signal & slot.

i created these functions:

myClass.h
 
public:
QCalendarWidget *cal;
 
public slots:
void writeDate(QLabel *);
void func();
void openCal();
 
signals:
void calClicked(QLabel *);

myClass.h

public:
QCalendarWidget *cal;

public slots:
void writeDate(QLabel *);
void func();
void openCal();

signals:
void calClicked(QLabel *);

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myClass.cpp
 
connect(btn,SIGNAL(clicked()),this,SLOT(openCal())); //it works
connect(cal,SIGNAL(clicked(QDate)),this,SLOT(func()));//it works
myClass *a,*b;
QObject::connect(a, SIGNAL(calClicked(lbl)), b, SLOT(writeDate(lbl)));//it never works
 
void myClass::func()
{
      emit calClicked(lbl);
}
 
void myClass::writeDate(QLabel *lbl)
{
    cal->close();
    lbl->setText(cal->selectedDate());
}

myClass.cpp

connect(btn,SIGNAL(clicked()),this,SLOT(openCal())); //it works
connect(cal,SIGNAL(clicked(QDate)),this,SLOT(func()));//it works
myClass *a,*b;
QObject::connect(a, SIGNAL(calClicked(lbl)), b, SLOT(writeDate(lbl)));//it never works

void myClass::func()
{
      emit calClicked(lbl);
}

void myClass::writeDate(QLabel *lbl)
{
    cal->close();
    lbl->setText(cal->selectedDate());
}

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but i always get error:QObject::connect: Cannot connect (null)::calClicked(lbl) to (null)::writeDate(lbl)


sorry for my english.

[Zlatomir]

Make sure that a and b pointers are initialized?

//I don't really follow why you need two objects of that class? Shouldn't the functionality you talk about happen inside the object? Anyway this might be me - because i don't see the whole application code, so just check the pointers if i'm wrong with this part.

LE: also the connect syntax is incorrect, if should be QLabel* instead of lbl. //you pass lbl when you emit the signal - at the connect you say only the parameter type.