Why we write QWidget *parent=0?

mit_cruze

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QDebug>



namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private slots:
    void on_ok_button_clicked();
    void on_cancel_button_clicked();

private:
    Ui::MainWindow *ui;
};

What is meant by explicit MainWindow(QWidget *parent=0)?
why we write Qwidget *parent=0?
Is itokay if we dont write explicit?

? Offline

Hi!

Cheers!

Jan-Willem

When you write:

explicit MainWindow(QWidget *parent);

you will have to assign a parent, because it expects an argument.
But when you write:

explicit MainWindow(QWidget *parent = 0);

you don't have to assign a parent, as it has already a default argument.

As for the second question, perhaps this gives you some insight?
https://msdn.microsoft.com/en-us/library/wwywka61.aspx

tham

As a side note, nullptr is a better replacement for 0.

Buckwheat

@tham ... I agree that the use of '0' is not good for pointers as it is ambiguous. But, for < c++11 nullptr is not defined. That being said, Q_NULLPTR could be used and that would be, at least, more readable as to intent.