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C-/C++-Quelltext

#include <iostream>

class foo
{
public:
    foo() : x(0)
    {}

    virtual ~foo() {}

private:
    int x;
};

class bar : public foo
{
public:
    bar(int param) : y(param), foo()
    {}

    int getY() { return y; }

private:
    int y;
};

int main()
{
    foo *pFirst(new bar(5));
    foo *pSec(new bar(1));

    *pSec = *pFirst;
    std::cout << dynamic_cast<bar*>(pSec)->getY() << std::endl; // gibt 1 aus obwohl ich 5 erwartet hätte
    system("pause");
}

C-/C++-Quelltext

class A {
public:
  virtual A& operator= (const A& a) {
    assign(a);
    return *this;
  }

protected:
  void assign(const A& a) {
    // copy members of A from a to this
  }
};

class B : public A {
public:
  virtual B& operator= (const A& a) {
    if (const B* b = dynamic_cast<const B*>(&a))
      assign(*b);
    else
      throw bad_assignment();
    return *this;
  }

protected:
  void assign(const B& b) {
    A::assign(b); // Let A's assign() copy members of A from b to this
    // copy members of B from b to this
  }
}