Double pointer error // please help me

[Kycho]

Hello, everyone.

I used double pointers.
And I'm in a strange situation that I do not understand, please help me.

The problem is in the 'roomOnClick' function.

(The original source was too long to be compressed as much as possible.)

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>

namespace Ui {class MainWindow;}

class Room;

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;
    Room *room[900];
    Room **selectRoom; 


private slots:
    void roomOnClick(Room *ptr);


signals:

};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "room.h"
#include "billacceptor.h"
#include "billdispensor.h"
#include "receiptprinter.h"
#include "network.h"
#include <QDebug>
#include <QTimer>
#include <QSerialPortInfo>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->stackedWidget->setCurrentWidget(ui->selectRoomPage);
    ui->sleepingRoomButton->setEnabled(false);
    ui->takeRoomButton->setEnabled(false);

    createRoom("101","100","500",Room::take_sleepRoom);
    createRoom("102","200","1000",Room::take_sleepRoom);
    createRoom("103","300","1500",Room::take_sleepRoom);
    createRoom("105","400","2000",Room::take_sleepRoom);
    createRoom("106","500","2500",Room::take_sleepRoom);
    createRoom("107","600","3000",Room::take_sleepRoom);
    createRoom("108","700","3500",Room::take_sleepRoom);
    createRoom("109","800","4000",Room::take_sleepRoom);
    createRoom("110","900","4500",Room::take_sleepRoom);
}
void MainWindow::roomOnClick(Room *ptr)
{
    selectRoom = &ptr;
    ui->roomselectImageLabel->setText(selectRoom[0]->getRoomId());
    ui->sleepPriceLabel->setText(selectRoom[0]->getSleepPirce());
    ui->takePriceLabel->setText(selectRoom[0]->getTakePrice());
    ui->sleepingRoomButton->setEnabled(true);
    ui->takeRoomButton->setEnabled(true);
    qDebug() << selectRoom[0] << selectRoom;
}
void MainWindow::createRoom(const QString &_roomId , const QString &_takePrice ,
                            const QString &_sleepPrice , int _sellType)
{
   room[Room::count] = new Room(_roomId,_takePrice,_sleepPrice,_sellType);
   connect(room[Room::count],&Room::roomClicked,this,&MainWindow::roomOnClick);

   // 3*3 GridLayout setup
   int page = Room::count / 9;
   int row = Room::count % 9 / 3;
   int column = Room::count % 3;
   if(row == 0 && column == 0){
       roomPage[page] = new QWidget;
       roomLay[page] = new QGridLayout;
       roomPage[page]->setLayout(roomLay[page]);
       ui->roomStack->addWidget(roomPage[page]);
   }
   roomLay[page]->addWidget(room[Room::count],row,column);
}

'selectRoom' is a double pointer to 'room'.
The 'selectRoom' (double pointer) inside the 'roomOnClick' function works as I intended.
But, when the function 'roomOnClick' is terminated, the address value stored in 'selectRoom' is destroyed.

I do not understand why it is annihilated.
How do I solve this problem?
Please help me.

[jsulm]

@Kycho Instead of messing up with raw pointers you should use a container like QVector to store your Room instances.
So, I suggest to change

Room *room[900];
Room **selectRoom;

to

QVector<Room> rooms;
int selectedRoomIndex;

Also, why do you do

selectRoom = &ptr;

?
Isn't ptr a pointer to a specific Room instance? I really don't see a need for a pointer to a pointer here.

[Kycho]

@jsulm

Thank you.
I will change according to your advice.

[Kycho]

@jsulm

I modified the source according to your advice and the problem is completely resolved.

Thank you!!

mainwindow.cpp

void MainWindow::createRoom(const QString &_roomId , const QString &_takePrice ,
                            const QString &_sleepPrice , int _sellType)
{
    rooms.append(new Room(_roomId,_takePrice,_sleepPrice,_sellType));
    int currentRoomIndex = rooms.count()-1;
    connect(rooms.at(currentRoomIndex),&Room::roomClicked,this,&MainWindow::roomOnClick);
   // 3*3 GridLayout setup
    int page = currentRoomIndex / 9;
    int row = currentRoomIndex % 9 / 3;
    int column = currentRoomIndex % 3;
    if(row == 0 && column == 0){
        roomPage[page] = new QWidget;
        roomLay[page] = new QGridLayout;
        roomPage[page]->setLayout(roomLay[page]);
        ui->roomStack->addWidget(roomPage[page]);
    }
    roomLay[page]->addWidget(rooms.at(currentRoomIndex),row,column);
}

void MainWindow::roomOnClick(Room *ptr)
{
    selectRoomIndex = rooms.indexOf(ptr);
    ui->roomselectImageLabel->setText(rooms.at(selectRoomIndex)->getRoomId());
    ui->sleepPriceLabel->setText(rooms.at(selectRoomIndex)->getSleepPirce());
    ui->takePriceLabel->setText(rooms.at(selectRoomIndex)->getTakePrice());
    ui->sleepingRoomButton->setEnabled(true);
    ui->takeRoomButton->setEnabled(true);
}