7 Expressions [expr]

7.6 Compound expressions [expr.compound]

7.6.1 Postfix expressions [expr.post]

7.6.1.8 Type identification [expr.typeid]

The result of a typeid expression is an lvalue of static type const std::type_info ([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].53

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.

If the type of the expression or type-id operand is a (possibly cv-qualified) class type or a reference to (possibly cv-qualified) class type, that class shall be completely defined.

If an expression operand of typeid is a possibly-parenthesized unary-expression whose unary-operator is * and whose operand evaluates to a null pointer value ([basic.compound]), the typeid expression throws an exception ([except.throw]) of a type that would match a handler of type std::bad_typeid ([bad.typeid]).

[Note 1:

In other contexts, evaluating such a unary-expression results in undefined behavior ([expr.unary.op]).

— end note]

When typeid is applied to a glvalue whose type is a polymorphic class type ([class.virtual]), the result refers to a std::type_info object representing the type of the most derived object ([intro.object]) (that is, the dynamic type) to which the glvalue refers.

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.

[Note 2:

The type-id cannot denote a function type with a cv-qualifier-seq or a ref-qualifier ([dcl.fct]).

— end note]

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 1: 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]

The type std::type_info ([type.info]) is not predefined; if a standard library declaration ([typeinfo.syn], [std.modules]) of std::type_info does not precede ([basic.lookup.general]) a typeid expression, the program is ill-formed.

[Note 3:

Subclause [class.cdtor] describes the behavior of typeid applied to an object under construction or destruction.

— end note]

53)53)

The recommended name for such a class is extended_type_info.