c,cc/derived.cc


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#include <iostream>
#include <vector>

using namespace std;

struct Base {
  virtual int
  index() { return -1; };
};

struct D1 : public Base {
  int idx = 1;

  virtual int
  index() { return idx; }
};

int
main(void)
{
  vector<Base*> v;
  D1* d = new D1;
  v.push_back(d);
  cout << v.back()->index() << endl;

  return 0;
}