Could you tell me how to use value in main.cpp?

[masayoshi]

Could you modify my code.?
I would like to see " MainWindow : I have a : "dog"

// mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    qDebug() << "MainWindow : I have a  : " << pet;
}

MainWindow::~MainWindow()
{
    delete ui;
    qDebug() << "~MainWindow : I have a  : " << pet;
}

// main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    qDebug() << "Main";
    MainWindow w;   
    w.pet = "dog";
    w.show();

    return a.exec();
}

// mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QtDebug>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    QString pet;

private:
    Ui::MainWindow *ui;

};

#endif // MAINWINDOW_H

[mrjj]

Hi
You print the
qDebug() << "MainWindow : I have a : " << pet;
before you set pet to dog.

..main..
MainWindow w; <<< you print here
w.pet = "dog"; << but set it first here

So you can give it via the constructor ( also add in .h )
explicit MainWindow(QWidget *parent = nullptr, QString petType);

MainWindow::MainWindow(QWidget *parent, QString petType) :
    QMainWindow(parent), pet(pettype) <<< set it
    ui(new Ui::MainWindow)
{
....

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    qDebug() << "Main";
    MainWindow w(nullptr,"dog");   
    w.show();
    return a.exec();
}

Or
you can add a function setPet(QString petType) that both sets
the pet variable and do
qDebug() << "MainWindow : I have a : " << pet;

[masayoshi]

Thank you for reply.
Sorry , I can not modify code well.
Please correct my code.

// mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent, QString petType) :
QMainWindow(parent), pet (petType),
ui(new Ui::MainWindow)

//MainWindow::MainWindow(QWidget *parent) :
// QMainWindow(parent),
// ui(new Ui::MainWindow)
{
ui->setupUi(this);
qDebug() << "MainWindow : I have a : " << pet;
}

MainWindow::~MainWindow()
{
delete ui;
qDebug() << "~MainWindow : I have a : " << pet;
}

// mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QtDebug>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
//    explicit MainWindow(QWidget *parent = nullptr);

    explicit MainWindow(QWidget *parent = nullptr, QString petType);

    ~MainWindow();
    QString pet;

private:
    Ui::MainWindow *ui;

};

#endif // MAINWINDOW_H

// main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    qDebug() << "Main";
    MainWindow w(nullptr,"dog");

    w.show();

    return a.exec();
}

[mrjj]

Hi
you seem to have done it right.
we add a new parameter to the constructor of main window ( in .h)
explicit MainWindow(QWidget *parent = nullptr, QString petType);

and set our internal variable with it ( in .cpp)
MainWindow::MainWindow(QWidget *parent, QString petType) :
QMainWindow(parent), pet (petType), <<<< this is actually like pet = petType;
ui(new Ui::MainWindow)
...

and from main, when we do
MainWindow w(nullptr,"dog");

that "dog" is petType and we copy it to our variable in the class called pet.

[masayoshi]

Thank you.
I got the following error.
Sorry , i need your help.

//your code here
make: stopped in /usr/home/masayoshi/Qt/build-sample-Desktop-Debug
--- moc_mainwindow.o ---
In file included from moc_mainwindow.cpp:9:
./../sample/mainwindow.h:18:60: error: missing default argument on parameter 'petType'
    explicit MainWindow(QWidget *parent = nullptr, QString petType);
                                                           ^

//your code here

--- main.o ---
In file included from ../sample/main.cpp:1:
../sample/mainwindow.h:18:60: error: missing default argument on parameter 'petType'
    explicit MainWindow(QWidget *parent = nullptr, QString petType);

[aha_1980]

@masayoshi said in Could you tell me how to use value in main.cpp?:

explicit MainWindow(QWidget *parent = nullptr, QString petType);

You have to change the declaration in mainwindow.h to this:

explicit MainWindow(QWidget *parent, QString petType);

Then you can call it from main.cpp like this: MainWindow w(nullptr,"dog");

Regards

[masayoshi]

@aha_1980 said in Could you tell me how to use value in main.cpp?:

explicit MainWindow(QWidget *parent, QString petType);

It works. Thank you.

[SGaist]

Hi,

Side note, it's usual (but not mandatory) to put the parent parameter as last one with a default value of nullptr (unless you really need a parent in which case, don't give it a default value).