Question

Not sure this issue about Qt or C++ in general, I’m just a newbie for both of these!
I got a simple Qt app, with a MainWindow and Hello class like below:

hello.h

#ifndef HELLO_H
#define HELLO_H

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

class Hello : public QWidget
{
    Q_OBJECT
public:
    explicit Hello(MainWindow *parent = 0);

signals:

public slots:

};

#endif // HELLO_H

heloo.cpp

#include "hello.h"

Hello::Hello(MainWindow *parent) :
    QWidget(parent)
{
//nothing here yet
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QtGui/QMainWindow>
#include "hello.h"

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Hello* hi;
};

#endif // MAINWINDOW_H

mainwindows.cpp

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    hi = new Hello(this);
}

MainWindow::~MainWindow()
{

}

main.cpp

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

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

---

and here is the error when I build my project:

from ../untitled1/main.cpp:2: ../untitled1/hello.h:11: error: expected
‘)’ before ‘*’ token

and the line cause the error is:

explicit Hello(MainWindow *parent = 0);

Can you help me to resolve the issue!
Thanks you!

Answer 1

You have circular inclusion of header files in “hello.h” and “maindwindow.h”. There is no need to include these files in the header file as you are just using a pointer. A simple forward declaration such as class MainWindow; in “hello.h” is sufficient.