Question

If I define the function in mainwindow.cpp the function works, but when I define it in radiobuttons.cpp, and attempt to call it from mainwindow.cpp, the project won’t compile.

mainwindow.h

    #ifndef MAINWINDOW_H
    #define MAINWINDOW_H        
    #include <QMainWindow>

    namespace Ui {
    class MainWindow;
    }

    class MainWindow : public QMainWindow
    {
        Q_OBJECT

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

            void build_radios();  //this function

            ~MainWindow();

    };    
#endif // MAINWINDOW_H

radiobuttons.cpp

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

    void MainWindow::build_radios()
     {  

    //... some code

     }

mainwindow.cpp

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

void MainWindow::radio_buttons();   //error: C2761: 'void MainWindow::build_radios(void)' : member function redeclaration not allowed

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

{

radio_buttons();

}

Answer 1

That’s not a definition, the compiler sees it as a declaration of a member function outside the class definition, which is illegal. Just remove that line. It shouldn’t be there in the first place, it has no use.

In fact, move the actual definition from radiobuttons.cpp to mainwindow.cpp for consistency. Why declare a MainWindow member in a different implementation file?