dynamic_cast.cpp

来自「Advanced Internet Programming Lecture 2 」· C++ 代码 · 共 90 行

#include <iostream>
using namespace std;

class Base {
public:
  virtual void f() { cout << "Inside Base\n"; }
  // ...
};

class Derived : public Base {
public:
  void f() { cout << "Inside Derived\n"; }
};

int main()
{
  Base *bp, b_ob;
  Derived *dp, d_ob;

  dp = dynamic_cast<Derived *> (&d_ob);
  if(dp) {
    cout << "Cast from Derived * to Derived * OK.\n";
    dp->f();
  } else
    cout << "Error\n";

  cout << endl;

  bp = dynamic_cast<Base *> (&d_ob);
  if(bp) {
    cout << "Cast from Derived * to Base * OK.\n";
    bp->f();
  } else
    cout << "Error\n";

  cout << endl;

  bp = dynamic_cast<Base *> (&b_ob);
  if(bp) {
    cout << "Cast from Base * to Base * OK.\n";
    bp->f();
                 } else
    cout << "Error\n";

  cout << endl;

  dp = dynamic_cast<Derived *> (&b_ob);
  if(dp)
    cout << "Error\n";
  else
    cout << "Cast from Base * to Derived * not OK.\n";

  cout << endl;

  bp = &d_ob; // bp points to Derived object
  dp = dynamic_cast<Derived *> (bp);
  if(dp) {
    cout << "Casting bp to a Derived * OK\n" <<
      "because bp is really pointing\n" <<
      "to a Derived object.\n";
    dp->f();
  } else
    cout << "Error\n";

  cout << endl;

  bp = &b_ob; // bp points to Base object
  dp = dynamic_cast<Derived *> (bp);
  if(dp)
    cout << "Error";
  else {
    cout << "Now casting bp to a Derived *\n" <<
      "is not OK because bp is really \n" <<
      "pointing to a Base object.\n";
  }

  cout << endl;

  dp = &d_ob; // dp points to Derived object
  bp = dynamic_cast<Base *> (dp);
  if(bp) {
    cout << "Casting dp to a Base * is OK.\n";
                                                        bp->f();
  } else
    cout << "Error\n";

  return 0;
}