RTTI

typeid.cc

#include <iostream>
#include <typeinfo>

class Base {
 public:
  Base() : x_(0) {}
  virtual void print() { std::cout << "Base" << std::endl; }
 private:
  int x_;
};

class Sub : public Base {
 public:
  Sub() : y_(0) {}
  virtual void print() { std::cout << "Sub" << std::endl; }
 private:
  int y_;
};

class NoVirtualBase {
 public:
  NoVirtualBase() : z_(0) {}
  void print() { std::cout << "NoVirtualBase" << std::endl; }
 private:
  int z_;
};

class NoVirtualSub: public NoVirtualBase {
 public:
  NoVirtualSub() : w_(0) {}
  void print() { std::cout << "NoVirtualSub" << std::endl; }
 private:
  int w_;
};

int main() {
  Base b;
  Sub s;
  Base* p = static_cast<Base*>(&s);

  NoVirtualBase nb;
  NoVirtualSub ns;
  NoVirtualBase* np = static_cast<NoVirtualBase*>(&ns);

  std::cout << typeid(  b).name() << std::endl; // 4Base
  std::cout << typeid(  s).name() << std::endl; // 3Sub
  std::cout << typeid( *p).name() << std::endl; // 3Sub

  std::cout << typeid( nb).name() << std::endl; // 13NoVirtualBase
  std::cout << typeid( ns).name() << std::endl; // 12NoVirtualSub
  std::cout << typeid(*np).name() << std::endl; // 13NoVirtualBase <= It's not NoVirtualSub!

  std::cout << typeid( &b).name() << std::endl; // P4Base
  std::cout << typeid( &s).name() << std::endl; // P3Sub
  std::cout << typeid(  p).name() << std::endl; // P4Base

  std::cout << typeid(&nb).name() << std::endl; // P13NoVirtualBase
  std::cout << typeid(&ns).name() << std::endl; // P12NoVirtualSub
  std::cout << typeid( np).name() << std::endl; // P13NoVirtualBase

  void* vb = &b;
  void* vs = &s;

  void* vnb = &nb;
  void* vns = &ns;

  std::cout << typeid( vb).name() << std::endl; // Pv
  std::cout << typeid( vs).name() << std::endl; // Pv

  std::cout << typeid(vnb).name() << std::endl; // Pv
  std::cout << typeid(vns).name() << std::endl; // Pv

  return 0;
}

Comments are gcc's case.

Same for the latest Clang.

Please look at the line 51 for RTTI and vtables.

typeid() looks type of any "variable" in source code. But, runtime object type is only available in objects with vtables.