How to make it possible to create an instance of class B only after an instance of class A been created?

  • 2
    You'd better describe your task. What you are asking is like trying to solve a problem incorrectly - ixSci
  • If you are given an exhaustive answer, mark it as correct (a daw opposite the selected answer). - Nicolas Chabanovsky ♦

2 answers 2

Constructor B must accept A or some object that can only be obtained from A :

 struct B { B(const A&); };
  • Otherwise nothing ?? - ilyaoleynikov
  • @ilyaoleynikov in a normal way - no. - Abyx

Your task can be interpreted in two ways. If like “if no A created in the program, then creation B should generate an exception” - then this is one ... Here I would suggest in class A monitor the presence with, for example, a class variable (not an instance) and check it in constructor class B

If it is necessary that, before creating B , it is necessary to create — anywhere, whatever — an object A , then you can use the static variable A in the constructor B An even simpler option is to add object A to class B as a member — then it will definitely be created before creating B