Strange errors with my code

[tomy]

Hi guys,

Please look at my code.
This is Hello.h:

#ifndef HELLO_H
#define HELLO_H

#include <QDialog>

class QCheckBox;
class QLabel;
class QLineEdit;
class QPushButton;

class Hello : public QDialog
{
    Q_OBJECT
public:
    Hello(QWidget* parent = 0);

signals:
    void findNext(const QString& str, Qt::CaseSensitivity cs);
    void findPrevious(const QString& str, Qt::CaseSensitivity cs);

private slots:
    void findClicked();
    void enableFindButton(const QString& text);

private:
    QLabel* label;
    QLineEdit* lineEdit;
    QCheckBox* caseCheckBox;
    QCheckBox* backwardCheckBox;
    QPushButton* findButton;
    QPushButton* closeButton;
};

#endif // HELLO_H

And this one, Hello.cpp

#include <QtWidgets>
#include "hello.h"

Hello::Hello(QWidget *parent)
    : QDialog(parent)
{
    label = new QLabel(tr("Find &What"));
    lineEdit = new QLineEdit;
    label -> setBuddy(lineEdit);

    caseCheckBox = new QCheckBox (tr("Match &case"));
    backwardCheckBox = new QCheckBox (tr("Search &backward"));

    findButton = new QPushButton (tr("&Find"));
    findButton -> setDefault(true);
    findButton -> setEnabled(false);
    closeButton = new QPushButton(tr("Close"));

    connect(lineEdit, SIGNAL(textChanged(const QString&)),
            this, SLOT(enableFindButton(const QString&)));
    connect(findButton, SIGNAL(clicked()),
            this, SLOT(findClicked()));
    connect(closeButton, SIGNAL(clicked()),
            this, SLOT(close()));

    QHBoxLayout* topLeftLayout = new QHBoxLayout;
    topLeftLayout -> addWidget(label);
    topLeftLayout -> addWidget(lineEdit);

    QVBoxLayout* leftLayout = new QVBoxLayout;
    leftLayout -> addLayout(topLeftLayout);
    leftLayout -> addWidget(caseCheckBox);
    leftLayout -> addWidget(backwardCheckBox);

    QVBoxLayout* rightLayout = new QVBoxLayout;
    rightLayout -> addWidget(findButton);
    rightLayout -> addWidget(closeButton);
    rightLayout -> addStretch();

    QHBoxLayout* mainLayout = new QHBoxLayout;
    mainLayout -> addLayout(leftLayout);
    mainLayout -> addLayout(rightLayout);
    setLayout(mainLayout);

    setWindowTitle((tr("Find")));
    setFixedHeight(sizeHint().height());
}

//-------------------------------------------------------

void Hello::findClicked()
{
    QString text = lineEdit -> text();
    Qt::CaseSensitivity cs = caseCheckBox -> isChecked() ? Qt::CaseSensitive
                                                         : Qt::CaseInsensitive;
    if(backwardCheckBox -> isChecked()) {
        emit findPrevious(text, cs);
    } else {
        emit findNext(text, cs);
    }
}

//-------------------------------------------------

void Hello::enableFindButton(const QString& text)
{
    findButton -> setEnabled(!text.isEmpty());
}

And this, main.cpp:

#include <QApplication>
#include <hello.h>

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    Hello* dialog = new Hello;
    dialog -> show();

    return app.exec();
}

I get some strange errors that I don't know the reason for them, like:
C:\Users...\Qt\Hello\hello.cpp:5: error: undefined reference to `vtable for Hello'.

This is for line 5 of Hello.cpp ( : QDialog(parent))

Would you please help me?

[koahnig]

You try to assign a QWidget pointer to QDialog.

Change to

class Hello : public QDialog
{
    Q_OBJECT
public:
    Hello(QDialog* parent = 0);

and

Hello::Hello(QDialog *parent)
    : QDialog(parent)

[tomy]

@koahnig :
Thanks for the answer. I understand your reason but do you have the book C++-GUI-Programming-with-Qt-4-2ndEdition on your hand to have a look at page 29 of it?
There it mentions these:

class Hello : public QDialog
{
    Q_OBJECT
public:
    Hello(QWidget* parent = 0);

and

Hello::Hello(QWidget *parent)
    : QDialog(parent)
{

I also modified my code as you suggested but get the errors yet! :(

[mrjj]

Hi

• "undefined reference to `vtable "

From build menu, try
Clean All
qmake
Build All

[tomy]

@mrjj said in Strange errors with my code:

Hi

• "undefined reference to `vtable "

From build menu, try
Clean All
qmake
Build All

Thank you. You solved the issues.

Could I ask why I faced this kind of problem? What was the reason?

[koahnig]

Sometimes a fresh rebuild simply helps.

Especially when you have a lot of different source and header not all dependencies are always covered and the system cannot detect.
This is just a trial to explain, it is very often a mystery to me why you are ending up in such failures.

The sequence given by @mrjj is basically some sort of Ctrl+Alt+Del for Qt creator

[kshegunov]

@tomy said in Strange errors with my code:

What was the reason?

Stale translation units (object files). Probably Creator missed that you changed something, just as @koahnig explained, and didn't recompile the .cpp, which in turn led to the linker error.

[SGaist]

Hi,

To add to my fellows, the vtable error usually comes when adding/removing the Q_OBJECT macro. This one requires to re-run qmake to refresh the build setup with the add/removed information.

[tomy]

So whenever I will see such error (vtable) again, I will do the steps mrjj said. :)
Thanks so much to all, especially to SGaist for his simple language.