[QT] subclassing

#include <QTableWidget>
class QLabel;
class QPushButton;
class QLineEdit;
class TablePay :public QTableWidget{
Q_OBJECT
        public:
        TablePay(QWidget* parent = 0);
        //signals:
        //void HellofromTablePay(const QString&);
        private slots:
        void getHello(const QString&);
        private:
        QString t_str;
};
#endif // CTABLEPAYS_H

#include <QtGui>
#include "CTablePays.h"

TablePay::TablePay(QWidget* parent)
        :QTableWidget(parent)
{

    t_str="hello,world";
}


void TablePay::getHello(const QString& s)
{
    t_str=s;
}

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QtGui/QMainWindow>
#include "CTablePays.h"
namespace Ui
{
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;
    QTableWidget* buf_p;
    //TablePay* real_p;
};

#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "CTablePays.h"
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent), ui(new Ui::MainWindow),buf_p(new TablePay(ui->buf_pay))//,real_p(&TablePay(ui->real_pay))
{
    ui->setupUi(this);
}

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