How to make d-pointer right in Qt -

i've created myclass class , in order hide members, used d-pointer got error while compiling souce code. here code:

header file:

class myclassprivate;  class myclass : public qobject {     q_object public:     myclass(qobject *parent = 0);     ~myclass();     ... signals:  public slots:  private:     myclassprivate *d; }; 

and related .cpp

myclass::myclass(qobject *parent):     qobject(parent),     d(new myclassprivate()) { }  myclass::~myclass() {     delete d; }  class myclassprivate {   public:     myclassprivate();     ...some methods...     qtextstream stream;     qfile* m_file; };  myclassprivate::myclassprivate():     m_file(new qfile) { } 

it says: forward declaration of 'struct myclassprivate'; invalid use of incomplete type 'myclassprivate'

you have put myclassprivate declaration before using in myclass constructor. in .cpp file:

class myclassprivate {     // ... };  myclass::myclass(qobject *parent):     qobject(parent),     d(new myclassprivate()) { } 

you might want check out sources on web explaining concept , qt's convenience macros q_d, q_declare_private , on:

1. blog post on qt private classes , d-pointers
2. kde techbase on d-pointers