[Solved] how do we properly create a C-style or traditional casting in cpp, with custom type/class/struct

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We have this kind of set-up; a custom classes

class Base {
//    public:
//        virtual void funcBase();
};

class DeriveOne : public Base {
    public:
        char* funcDeriveOne();
//        void funcBase() final override;
};

Class DeriveTwo : public Base {
    public:
        bool funcDeriveTwo();
//        void funcBase() final override;
};

What I have tried:

we have this func that accept Base or Derive classes as an arguments and without returning anything.

void func(const Base& base) {
    std::cout << (DeriveOne&)base.funcDeriveOne() << std::endl;
    std::cout << (DeriveTwo&)base.funcDeriveTwo() << std::endl;
}

Posted 18-May-22 22:03pm

Phoenix Liveon

Updated 22-May-22 3:00am

v3

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CPallini · Accepted Answer · 2022-05-18T22:53:00

Don't use C-like casts in C++ code.
C++ features dynamic_cast. Try

C++

#include <iostream>
using namespace std;

class Base
{
public:
  virtual void funcBase() = 0;
  virtual ~Base(){}
};

class DeriveOne : public Base
{
public:
  const char* funcDeriveOne(){  return "hi";}
  void funcBase() final override
  {
  }
  virtual ~DeriveOne(){}
};

class DeriveTwo : public Base
{
public:
  bool funcDeriveTwo() { return true;}
  void funcBase() final override
  {
  }
  virtual ~DeriveTwo(){}
};


void func( Base & base)
{
  try
  {
    cout << dynamic_cast<DeriveOne & >(base).funcDeriveOne() << endl;
  }
  catch (exception & e)
  {
    cout << e.what() << " (DeriveOne)" << endl;
  }
  try
  {
    cout << dynamic_cast<DeriveTwo & >(base).funcDeriveTwo() << endl;
  }
  catch(exception & e)
  {
    cout << e.what() << " (DeriveTwo)" << endl;
  }
}

int main()
{
  Base * pdo = new DeriveOne();
  Base * pdt = new DeriveTwo();

  func(*pdo);
  cout << "--------" << endl;
  func(*pdt);

  delete pdt;
  delete pdo;
}

Quote:
is there another way to cast it down in a traditional or legacy sort of way?

Of course, you can:

C++

void func_c_cast( Base & base )
{
  cout << (*(DeriveOne *)&base).funcDeriveOne() << endl;
  cout << (*(DeriveTwo *)&base).funcDeriveTwo() << endl;
}

However, you are looking for 'unexpected behaviour'.