Problem with slot

[stefek]

Hi!
I'm trying to develop a simple calculator. I'm using Qt Creator. I've already designed a form, but now I have a problem with slot. It calls, when i push the button with digit and adds the digit to lcd. I think everything is ok, but i get compiler's errors. Here is the source code:

//calc.h
 
#ifndef CALC_H
#define CALC_H
 
#include <QtGui/QDialog>
 
namespace Ui
{
    class Calc;
}
 
class Calc : public QDialog
{
    Q_OBJECT
 
public:
    Calc(QWidget *parent = 0);
    ~Calc();
 
slots:
    void setVal(const int &val);
 
private:
    Ui::Calc *ui;
};
 
#endif // CALC_H

//calc.h

#ifndef CALC_H
#define CALC_H

#include <QtGui/QDialog>

namespace Ui
{
    class Calc;
}

class Calc : public QDialog
{
    Q_OBJECT

public:
    Calc(QWidget *parent = 0);
    ~Calc();

slots:
    void setVal(const int &val);

private:
    Ui::Calc *ui;
};

#endif // CALC_H

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//calc.cpp
#include "calc.h"
#include "ui_calc.h"
 
Calc::Calc(QWidget *parent)
    : QDialog(parent), ui(new Ui::Calc)
{
    ui->setupUi(this);
}
 
Calc::~Calc()
{
    delete ui;
}
 
void Calc::setVal(const int &val){
 
    lcdNumber-> intValue*=10;
    lcdNumber -> intValue+=val;
}

//calc.cpp
#include "calc.h"
#include "ui_calc.h"

Calc::Calc(QWidget *parent)
    : QDialog(parent), ui(new Ui::Calc)
{
    ui->setupUi(this);
}

Calc::~Calc()
{
    delete ui;
}

void Calc::setVal(const int &val){

    lcdNumber-> intValue*=10;
    lcdNumber -> intValue+=val;
}

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And these are the errors:

calc.h:16: error: expected primary-expression before ‘void’
calc.h:16: error: ISO C++ forbids declaration of ‘type name’ with no type
calc.h:16: error: expected ‘;’ before ‘void’
calc.cpp:11: error: no ‘void Calc::setVal(const int&)’ member function declared in class ‘Calc’

Please help me
Regards
Stefek

[wysota]

It should say "public slots:" and not "slots:".

[stefek]

Thanks, this problem is solved, but now come other problems.

calc.h:18: error: ISO C++ forbids declaration of ‘QLCDNumber’ with no type
calc.h:18: error: expected ‘;’ before ‘*’ token

So I added the declaration of QLCDNumber class: class QLCDNumber;. and now are problems with the inside of the slot:

calc.cpp:17: error: invalid use of member (did you forget the ‘&’ ?)

How can I solve it?

I think i solve this problem. I add to class Calc new variable int value, which stores the actual result of calculations and use display function.

But... I have new problem...
Here is my source code:

//calc.h
 
#ifndef CALC_H
#define CALC_H
 
#include <QtGui/QDialog>
 
class QLCDNumber;
namespace Ui
{
    class Calc;
}
 
class Calc : public QDialog
{
    Q_OBJECT
 
     private:
          QLCDNumber *lcdNumber;
          QPushButton *seventhButton;
          QPushButton *eighthButton;
          QPushButton *ninethButton;
          QPushButton *divisionButton;
          QPushButton *fourthButton;
          QPushButton *fifthButton;
          QPushButton *sixthButton;
          QPushButton *additionButton;
          QPushButton *firstButton;
          QPushButton *secondButton;
          QPushButton *thirdButton;
          QPushButton *subtractionButton;
          QPushButton *zeroButton;
          QPushButton *sqrtButton;
          QPushButton *multiplicationButton;
          QPushButton *moduloButton;
          int value;
 
public:
    Calc(QWidget *parent = 0);
    ~Calc();
 
    public slots:
          void setVal(const int &val);
 
 
 
private:
    Ui::Calc *ui;
};
 
#endif // CALC_H

//calc.h

#ifndef CALC_H
#define CALC_H

#include <QtGui/QDialog>

class QLCDNumber;
namespace Ui
{
    class Calc;
}

class Calc : public QDialog
{
    Q_OBJECT

     private:
          QLCDNumber *lcdNumber;
          QPushButton *seventhButton;
          QPushButton *eighthButton;
          QPushButton *ninethButton;
          QPushButton *divisionButton;
          QPushButton *fourthButton;
          QPushButton *fifthButton;
          QPushButton *sixthButton;
          QPushButton *additionButton;
          QPushButton *firstButton;
          QPushButton *secondButton;
          QPushButton *thirdButton;
          QPushButton *subtractionButton;
          QPushButton *zeroButton;
          QPushButton *sqrtButton;
          QPushButton *multiplicationButton;
          QPushButton *moduloButton;
          int value;

public:
    Calc(QWidget *parent = 0);
    ~Calc();

    public slots:
          void setVal(const int &val);



private:
    Ui::Calc *ui;
};

#endif // CALC_H

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#include "calc.h"
#include "ui_calc.h"
 
Calc::Calc(QWidget *parent)
    : QDialog(parent), ui(new Ui::Calc)
{
    ui->setupUi(this);
    connect(zeroButton, SIGNAL(clicked()), this, SLOT(setVal(0)));
}
 
Calc::~Calc()
{
    delete ui;
}
 
void Calc::setVal(const int &val){
 
    value*=10;
    value+=val;
    lcdNumber ->display(value);
}

#include "calc.h"
#include "ui_calc.h"

Calc::Calc(QWidget *parent)
    : QDialog(parent), ui(new Ui::Calc)
{
    ui->setupUi(this);
    connect(zeroButton, SIGNAL(clicked()), this, SLOT(setVal(0)));
}

Calc::~Calc()
{
    delete ui;
}

void Calc::setVal(const int &val){

    value*=10;
    value+=val;
    lcdNumber ->display(value);
}

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In the constructor I add the conection between zero button and LCDNumber. It should works, but in the console are errors:

Segmentation fault

I have no idea how to do this. Could anyone help me?
It's harder than I thought at the beginning of lessons.

I've read in documentation that the signal and slot parameters mustn't contain variable name, but only type, so how can I send the value, which is needed?

[wysota]

Your original problem simply required including <QLCDNumber>. Your current problem is that you didn't create an object behind the zeroButton variable.

[talk2amulya]

u dont have to send any value from the slot..remove 0 from setVal(0) and it should work..the signal will IMPLICITLY send the data as required by the slot...in the case of clicked(bool), if the button is clicked, 'true' is the value sent, otherwise 'false' is sent

[stefek]

I've added in main function,after the Calc constructor, new procedure "connection" that connects signals with slots. The effect is the same = segfault.

Yes, there was error,but now is:

connect(this->zeroButton, SIGNAL(clicked(bool)), this, SLOT(setVal(const int &)));

connect(this->zeroButton, SIGNAL(clicked(bool)), this, SLOT(setVal(const int &)));

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And still is segfault.

[wysota]

Did you initialize the zeroButton variable to anything?

By the way, please read about signal-slot connections in the reference. You can't connect a bool signal to an int slot, it wouldn't make sense.

[stefek]

I've read this, but I can't write anything that could work. Is it really hard or do I make it more difficult than it is? :/
I think that actually the whole calculator is too difficult for me. I'll try to make simple dialog with one QPushButton and QLCDNumber.
I've written a function, which sets value to qlcdnumber:

void changeValue(const int &val){
 
     lcdNumber->display(val);
}

void changeValue(const int &val){

     lcdNumber->display(val);
}

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But no matter how I call this function I get segfaults. I don't know why.

[wysota]

I will repeat this question the last time - did you initialize your variables? Do you have any knowledge of C++ at all? Do you understand the difference between a pointer and an object? You are getting a segmentation fault because you try to dereference an uninitialized pointer. The control flow doesn't even reach the connect statement because it segfaults a while earlier.

[stefek]

Here is actual source code:

//dialog.cpp
#include "dialog.h"
#include "ui_dialog.h"
 
Dialog::Dialog(QWidget *parent)
    : QDialog(parent), ui(new Ui::DialogClass)
{
    ui->setupUi(this);
 
}
 
Dialog::~Dialog()
{
    delete ui;
}
 
void Dialog::changeValue(const int &val){
 
     lcdNumber->display(val);
}

//dialog.cpp
#include "dialog.h"
#include "ui_dialog.h"

Dialog::Dialog(QWidget *parent)
    : QDialog(parent), ui(new Ui::DialogClass)
{
    ui->setupUi(this);

}

Dialog::~Dialog()
{
    delete ui;
}

void Dialog::changeValue(const int &val){

     lcdNumber->display(val);
}

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//dialog.h
#ifndef DIALOG_H
#define DIALOG_H
 
#include <QtGui/QDialog>
class QLCDNumber;
namespace Ui
{
    class DialogClass;
}
 
class Dialog : public QDialog
{
    Q_OBJECT
 
public:
    Dialog(QWidget *parent = 0);
    ~Dialog();
 
public slots:
     void changeValue(const int &val);
 
     signals:
     void onClick(const int &val);
 
 
private:
     QLCDNumber *lcdNumber;
    Ui::DialogClass *ui;
};
 
#endif // DIALOG_H

//dialog.h
#ifndef DIALOG_H
#define DIALOG_H

#include <QtGui/QDialog>
class QLCDNumber;
namespace Ui
{
    class DialogClass;
}

class Dialog : public QDialog
{
    Q_OBJECT

public:
    Dialog(QWidget *parent = 0);
    ~Dialog();

public slots:
     void changeValue(const int &val);

     signals:
     void onClick(const int &val);


private:
     QLCDNumber *lcdNumber;
    Ui::DialogClass *ui;
};

#endif // DIALOG_H

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//ui_dialog.h
#ifndef UI_DIALOG_H
#define UI_DIALOG_H
 
#include <QtCore/QVariant>
#include <QtGui/QAction>
#include <QtGui/QApplication>
#include <QtGui/QButtonGroup>
#include <QtGui/QDialog>
#include <QtGui/QLCDNumber>
#include <QtGui/QPushButton>
 
QT_BEGIN_NAMESPACE
 
class Ui_DialogClass
{
public:
    QLCDNumber *lcdNumber;
    QPushButton *pushButton;
 
    void setupUi(QDialog *DialogClass)
    {
    if (DialogClass->objectName().isEmpty())
        DialogClass->setObjectName(QString::fromUtf8("DialogClass"));
    DialogClass->resize(209, 62);
    lcdNumber = new QLCDNumber(DialogClass);
    lcdNumber->setObjectName(QString::fromUtf8("lcdNumber"));
    lcdNumber->setGeometry(QRect(130, 20, 64, 23));
    pushButton = new QPushButton(DialogClass);
    pushButton->setObjectName(QString::fromUtf8("pushButton"));
    pushButton->setGeometry(QRect(10, 20, 105, 25));
    pushButton->setProperty("value", QVariant(0));
 
    retranslateUi(DialogClass);
 
    QMetaObject::connectSlotsByName(DialogClass);
    } // setupUi
 
    void retranslateUi(QDialog *DialogClass)
    {
    DialogClass->setWindowTitle(QApplication::translate("DialogClass", "Dialog", 0, QApplication::UnicodeUTF8));
    pushButton->setText(QApplication::translate("DialogClass", "0", 0, QApplication::UnicodeUTF8));
    Q_UNUSED(DialogClass);
    } // retranslateUi
 
};
 
namespace Ui {
    class DialogClass: public Ui_DialogClass {};
} // namespace Ui
 
QT_END_NAMESPACE
 
#endif // UI_DIALOG_H

//ui_dialog.h
#ifndef UI_DIALOG_H
#define UI_DIALOG_H

#include <QtCore/QVariant>
#include <QtGui/QAction>
#include <QtGui/QApplication>
#include <QtGui/QButtonGroup>
#include <QtGui/QDialog>
#include <QtGui/QLCDNumber>
#include <QtGui/QPushButton>

QT_BEGIN_NAMESPACE

class Ui_DialogClass
{
public:
    QLCDNumber *lcdNumber;
    QPushButton *pushButton;

    void setupUi(QDialog *DialogClass)
    {
    if (DialogClass->objectName().isEmpty())
        DialogClass->setObjectName(QString::fromUtf8("DialogClass"));
    DialogClass->resize(209, 62);
    lcdNumber = new QLCDNumber(DialogClass);
    lcdNumber->setObjectName(QString::fromUtf8("lcdNumber"));
    lcdNumber->setGeometry(QRect(130, 20, 64, 23));
    pushButton = new QPushButton(DialogClass);
    pushButton->setObjectName(QString::fromUtf8("pushButton"));
    pushButton->setGeometry(QRect(10, 20, 105, 25));
    pushButton->setProperty("value", QVariant(0));

    retranslateUi(DialogClass);

    QMetaObject::connectSlotsByName(DialogClass);
    } // setupUi

    void retranslateUi(QDialog *DialogClass)
    {
    DialogClass->setWindowTitle(QApplication::translate("DialogClass", "Dialog", 0, QApplication::UnicodeUTF8));
    pushButton->setText(QApplication::translate("DialogClass", "0", 0, QApplication::UnicodeUTF8));
    Q_UNUSED(DialogClass);
    } // retranslateUi

};

namespace Ui {
    class DialogClass: public Ui_DialogClass {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_DIALOG_H

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//main.cpp
#include <QtGui/QApplication>
#include "dialog.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Dialog w;
    w.show();
 
 
 
    return a.exec();
}

//main.cpp
#include <QtGui/QApplication>
#include "dialog.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Dialog w;
    w.show();


    
    return a.exec();
}

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I'm newbie in Qt and probably not C++ pro, but I want to learn and improve my skills.No one are the best at the beginning. Could you explain me how can I initialize variables? I'm in the brain dead.

[wysota]

Your problem is strictly related to C++. You have two lcdNumber member variables from different levels of inheritance and you use the one that is uninitialized. Get rid of lcdNumber from your Dialog class and use the one in ui.

[pastor]

I agree with wysota!

stefek, rewrite your code as follows:

void Dialog::changeValue(const int &val)
{ 
     ui->lcdNumber->display(val);
}

void Dialog::changeValue(const int &val)
{ 
     ui->lcdNumber->display(val);
}

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Also you should remove QLCDNumber *lcdNumber member from Dialog class declaration.