H:class Output : public QPlainTextEdit{ Q_OBJECTprivate: Output ();public: static Output* instance(); void release();public slots: void trace(const QString &text,const QColor &color);private: void echo(const QString &text); static Output* _instance;};CPP:Output* Output::_instance = 0;Output* Output::instance(){ if(!_instance) _instance = new Output(); return _instance;}void Output::release(){ if(_instance) { delete _instance; _instance = 0; }}