"undefined class" Qt/C++ - c++

Question

I recently started programming in C ++ and am having some difficulties in relation to the exchange of data between classes.
I searched many tutorials and examples, but none worked. I finally decided to ask for help because I do not know what do ...
PS: I want to call keyPressEvent function from my B (solEditor) class
thanks.
addons/soleditor.h (class)
#include <Qsci/qsciscintilla.h>
#include <QWidget>
#include <QKeyEvent>
class Editor; // main class
class solEditor : public QsciScintilla
{
public:
explicit solEditor(QWidget *parent = 0);
Editor editor; // error <<
protected:
void keyPressEvent(QKeyEvent *e);
};
editor.h (main window)
#include <QMainWindow>
#include "about.h"
#include "data.h"
#include "addons/codeeditor.h"
#include "addons/highlighter.h"
#include "addons/soleditor.h"
#include "plugins/headergenerator.h"
#include "plugins/updatescreen.h"
namespace Ui {
class Editor;
}
class solEditor;
class Editor : public QMainWindow
{
Q_OBJECT
solEditor *sE;
public:
QsciScintilla* ce;
Highlighter *Hl;
solEditor *e;
Ui::Editor *ui;
explicit Editor(QWidget *parent = 0);
~Editor();
public slots:
void on_KeyPress(QKeyEvent *e);
};
Error:
SOLEditor\addons\soleditor.h:14: error: C2079: 'solEditor::editor' uses undefined class 'Editor'

Answer 1

You are using a forward declaration
class Editor; // main class
with a local instance of that class
Editor editor; // error <<
Unfortunately, that is not possible, as in this case the compiler needs to know the full details of the Editor class.
There are two possible solutions:
Make the member a pointer: Editor* editor
Use an #include instead of a forward declaration.
If you want to make your code flexible, you could do it like this:
class solEditor : public QsciScintilla
{
public:
explicit solEditor(Editor* editor, QWidget* parent = 0);
inline Editor* editor() const { return _editor; }
private:
Editor* _editor;
}
and in the cpp file:
solEditor::solEditor(Editor* editor, QWidget* parent)
// TODO: call parent constructor
{
_editor = editor;
}
solEditor::~solEditor()
{
_editor = NULL;
}
You can then create a solEditor instance like this:
QWidget* optionalParentWidget = GetParentWidgetFromSomewhere();
Editor* editor = GetEditorInstanceFromSomewhere(); // or create it yourself
solEditor* myEditor = new solEditor(editor, optionalParentWidget);
(As a side node, classes in C++ usually start with a capital letter: QWidget, Editor, SolEditor. That makes it easier to spot if something is a class, a function or a variable).
About the key press event: If you want one class to handle certain events of another class, it's best to use the eventFilter mechanism:
http://qt-project.org/doc/qt-5/qobject.html#installEventFilter