c++ virtual function in constructor

In C++, virtual functions cannot be directly called from a constructor. This is because the construction of an object occurs before the object is fully initialized, and the virtual function table (vtable) is not set up until the object is fully constructed. However, there are ways to work around this limitation.

One approach is to provide a separate initialization function that is called after the object is constructed. This function can then call the virtual function. Here are the steps involved:

  1. Create a base class with a virtual function:
  2. Define a base class with a virtual function that you want to call from the constructor.

  3. This virtual function can be overridden in derived classes.

  4. Implement the derived class:

  5. Create a derived class that inherits from the base class.

  6. Override the virtual function in the derived class.

  7. Define a separate initialization function:

  8. In the derived class, define a public member function that will be called after the object is constructed.

  9. This function can be used to initialize any other members of the object as well.

  10. Call the initialization function:

  11. In the constructor of the derived class, call the initialization function after the object is fully constructed.

  12. This ensures that the virtual function can be called, as the vtable is now set up.

  13. Use the virtual function:

  14. Inside the initialization function, call the virtual function that was defined in the base class.
  15. This will invoke the appropriate implementation based on the actual type of the object.

By following these steps, you can work around the limitation of calling virtual functions directly from constructors in C++.