In template definitions, typename provides a hint to the compiler that an unknown identifier is a type. In template parameter lists, it's used to specify a type parameter.


typename identifier;


The typename keyword must be used if a name in a template definition is a qualified name that is dependent on a template argument; it's optional if the qualified name isn't dependent. For more information, see Templates and Name Resolution.

typename can be used by any type anywhere in a template declaration or definition. It isn't allowed in the base class list, unless as a template argument to a template base class.

template <class T>
class C1 : typename T::InnerType // Error - typename not allowed.
template <class T>
class C2 : A<typename T::InnerType>  // typename OK.

The typename keyword can also be used in place of class in template parameter lists. For example, the following statements are semantically equivalent:

template<class T1, class T2>...
template<typename T1, typename T2>...


// typename.cpp
template<class T> class X
   typename T::Y m_y;   // treat Y as a type

int main()

See also