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, C++ doesn't have anonymous classes like Java's.

You can define local classes, like this:

class B {
  public:
    A *a;
    b(){
       struct my_little_class : public A {
           void foo() {printf("hello");}
       };
       a = new my_little_class();
    }
};

Or maybe just a nested class:

class B {
  private:
    struct my_little_class : public A {
        void foo() {printf("hello");}
    };

  public:
    A *a;

    b(){
       a = new my_little_class();
    }
};

In C++03, local classes have some limitations (for example, they can't be used as template parameters) that were lifted in C++11.

In Java, anonymous classes are sometimes used to do what other languages do with anonymous functions like, for example, when you create an anonymous implementation of Runnable. C++11 has anonymous functions (also known as lambdas), so that could be an option if this is what you're trying to achieve.