typeid操作符

typeid() operator返回type_info，返回值不可拷贝、不可赋值

// Illustrates the typeid operator.
#include <iostream>
#include <typeinfo>
using namespace std;

struct PolyBase { virtual ~PolyBase() {} };
struct PolyDer : PolyBase { PolyDer() {} };

struct NonPolyBase {};
struct NonPolyDer : NonPolyBase { NonPolyDer(int) {} };

int main() {
  // Test polymorphic Types
  const PolyDer pd;
  const PolyBase* ppb = &pd;
  cout << typeid(ppb).name() << endl;
  cout << typeid(*ppb).name() << endl;
  cout << boolalpha << (typeid(*ppb) == typeid(pd))
       << endl;
  cout << (typeid(PolyDer) == typeid(const PolyDer))
       << endl;

  // Test non-polymorphic Types
  const NonPolyDer npd(1);
  const NonPolyBase* nppb = &npd;
  cout << typeid(nppb).name() << endl;
  cout << typeid(*nppb).name() << endl;
  cout << (typeid(*nppb) == typeid(npd)) << endl;

  // Test a built-in type
  int i;
  cout << typeid(i).name() << endl;

  return 0;

} ///:~

输出结果是：

struct PolyBase const *
struct PolyDer
true
true
struct NonPolyBase const *
struct NonPolyBase
false
int

The first output line just echoes the static type of ppb because it is a pointer. To get RTTI to kick in, you need to look at the pointer or reference destination object, which is illustrated in the second line. Notice that RTTI ignores top-level const and volatile qualifiers. With non-polymorphic types, you just get the static type (the type of the pointer itself). As you can see, built-in types are also supported.