Signal defined in "a.h" can not emit in "b.cpp"

[wysota]

Create a public method in A that will emit the signal.

class A : public QObject {
  Q_OBJECT
public:
  A(QObject *parent=0) : QObject(parent){}
  void emitSig(){ emit sig(); }
signals:
 void sig();
};

class A : public QObject {
  Q_OBJECT
public:
  A(QObject *parent=0) : QObject(parent){}
  void emitSig(){ emit sig(); }
signals:
 void sig();
};

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BTW. You should avoid emitting signals on account of other objects behind their back. If you do that, it's likely that your design is incorrect.