Is it possible to give a definition of a class in C++ during allocation, as is allowed in java

Question

Or simply put

can I do some thing like

class A {
public:
  virtual void foo() = 0;
};

class B {
  public:
    A *a;
    b(){
       a = new A() { vo         


        

Answer 1

No. Everything in C++ has to be defined before it can be used. In your case, since you want to override A::foo(), you have to derive a new class, and then B can instantiate that class, eg:

class A
{ 
public: 
  virtual void foo() = 0; 
}; 

class A1 : public A
{
public:
  void foo() { printf("hello"); }
}; 

class B
{ 
public: 
  A *a; 
  B()
  { 
    a = new A1(); 
  } 
};