Question

 class subscriber
 {
 public:
      virtual void update() = 0;
 }

 class entity : public subsriber
 {
 public:
      virtual void update() = 0;
 }

 class myObject : public entity
 {
 public:
      virtual void update()
       {
        do_things();
       }
 }

 subscriber * ptr = new myObject; //will use shared_ptr, but here i want simplicity

  ptr->update(); 

The question is, will the proper update function (the one implemented in myObject) be called? And is it valid to have 2 pure virtual functions with the same name in one “family”?

Answer 1

will the proper update function (the one implemented in myObject) be called?

Yes, it will be called.

is it valid to have 2 pure virtual functions with the same name in one “family”?

The second declaration (i.e. inside the entity class) does not introduce a second pure virtual function into the family: the signatures are identical, so update() is a single virtual function. Moreover, declaring it for the second time is not necessary: entity would remain abstract, and would have access to the update() method even if you removed the second declaration.