嵌套类的前向声明

Question

I am trying to forward delcare this nested class, I already tried it but i didnt work. When i try to forward declare i get cant acces private member errors, so I guess i am doing something wrong.

#ifndef PLAYERHOLDER_H
#define PLAYERHOLDER_H

#include <QtCore>
#include <player.h>
#include <datasource.h>

class PLAYERHOLDER
{

private:
class CONTACTMODEL : public QAbstractTableModel
{
public:
    explicit CONTACTMODEL(PLAYERHOLDER* holder);

    int rowCount( const QModelIndex &parent ) const;
    int columnCount( const QModelIndex &parent ) const;
    QVariant data( const QModelIndex &index, int role ) const;
    QVariant headerData( int section, Qt::Orientation orientation, int role ) const;
    void update();


private:
    static PLAYERHOLDER* m_playerHolder;
};

public:
static PLAYERHOLDER* getInstance();
void createPlayer(PLAYER *player);
void updatePlayer(int id);
void deletePlayer(int id);
PLAYER* findPlayer(int id);
void loadPlayers(int teamid);

QAbstractItemModel* model() ;

private:
PLAYERHOLDER();
static PLAYERHOLDER *thePlayerholder;
QHash<int, PLAYER*> playerlist;
DATASOURCE *datasource;
mutable CONTACTMODEL *m_model;
};

#endif // PLAYERHOLDER_H

But i dont know how to do it, i searched around and still dont know it :( Is it possible to forward declare this?

Answer 1

The nested type is part of the enclosing type. That means that it cannot be forward declared by itself, but it can be declared in the definition of the enclosing type, and then defined outside:

class enclosing {
   class inner;          // Forward declaration
};
// Somewhere else
class enclosing::inner { // Definition
   int x;
};

What you cannot do is forward declare the inner type outside of the definition of the enclosing type:

class enclosing::outer;  // Error