c++ - Define object from other classes -

i can't define object other classes under top class example :

class b;  class { public:          a(){ cout << "a\n"; }     ~a(){ cout << "~a\n"; } private: b ob; };  class b { public:     b(){ cout << "b\n"; }     ~b(){ cout << "~b\n"; }     ob; };  int main() {     b r;      system("pause");  } 

the problem can't make object in class if write (class b;) above it

your problem solved passing b object pointer a constructor. if change b class contain pointer a, recursion solved. is, creating infinite loop, creating object b contains object a, contains object b, , on.

class b { public:     b(a* _ob) : ob(_ob) { cout << "b\n"; }     ~b(){ cout << "~b\n"; }     a* ob; };  int main() {     _a;     b r(_a);      system("pause");  }