To block copying and assignment of an object, explicitly declare the assignment operator and copy constructor private. Don’t define them, (there’s no point in defining them because they can’t be invoked anyway): only declare them. In the following example, class A has a public default constructor. In addition, it declares a private copy constructor and assignment operator to ensure that objects of its class can’t be copied or assigned to:

 class a{public: A(){}private: A(const A&); // declared but not implemented A& operator=(const A&); // ditto};int main(){ A a; // fine, default ctor is public A b (a); // error, copy ctor is inaccessible A c; // fine c = a; // error, assignment operator is inaccessible}