I want to know the code QWidget * parent=0 is what meaning, and if the single from the c + +=0 is represent? Why not=0 if constructed object without parameters (such as MainWindows mw) would say there is no matching constructor, and added a=0 will not appear this error?

 # # ifndef MAINWINDOW_H 
# define MAINWINDOW_H 

#include  

The namespace Ui {
The class MainWindow. 
} 

The class MainWindow: public QMainWindow 
{
Q_OBJECT 

Public: 
Explicit MainWindow (QWidget * parent=0); 
~ MainWindow (); 

Private: 
Ui: : MainWindow * Ui; 
}; 

# endif//MAINWINDOW_H 

CodePudding user response:

Default constructor parameters, if you omit parameter, equal with the default value as a parameter,

CodePudding user response:

By default the null pointer