The result of a typeid expression is an lvalue of static type const std::type_info and dynamic type const std::type_info or const name where name is an implementation-defined class publicly derived from std::type_info which preserves the behavior described in [type.info].70 The lifetime of the object referred to by the lvalue extends to the end of the program. Whether or not the destructor is called for the std::type_info object at the end of the program is unspecified.
When typeid is applied to a glvalue expression whose type is a polymorphic class type, the result refers to a std::type_info object representing the type of the most derived object (that is, the dynamic type) to which the glvalue refers. If the glvalue expression is obtained by applying the unary * operator to a pointer71 and the pointer is a null pointer value, the typeid expression throws an exception of a type that would match a handler of type std::bad_typeid exception.
When typeid is applied to an expression other than a glvalue of a polymorphic class type, the result refers to a std::type_info object representing the static type of the expression. Lvalue-to-rvalue, array-to-pointer, and function-to-pointer conversions are not applied to the expression. If the expression is a prvalue, the temporary materialization conversion is applied. The expression is an unevaluated operand.
When typeid is applied to a type-id, the result refers to a std::type_info object representing the type of the type-id. If the type of the type-id is a reference to a possibly cv-qualified type, the result of the typeid expression refers to a std::type_info object representing the cv-unqualified referenced type. If the type of the type-id is a class type or a reference to a class type, the class shall be completely-defined.
If the type of the expression or type-id is a cv-qualified type, the result of the typeid expression refers to a std::type_info object representing the cv-unqualified type. [ Example:
class D { /* ... */ };
D d1;
const D d2;
typeid(d1) == typeid(d2); // yields true
typeid(D) == typeid(const D); // yields true
typeid(D) == typeid(d2); // yields true
typeid(D) == typeid(const D&); // yields true
— end example ]
[ Note: [class.cdtor] describes the behavior of typeid applied to an object under construction or destruction. — end note ]
The recommended name for such a class is extended_type_info.
If p is an expression of pointer type, then *p, (*p), *(p), ((*p)), *((p)), and so on all meet this requirement.