C++ in a Nutshell
| typename keyword | Introduces a type name |
| elaborated-type-specifier := typename [::] nested-name :: identifier typename [::] nested-name :: [template] template-id using-decl := using [typename] [::] nested-name :: unqualified-id ; type-parm := typename [ identifier ] [= id-expr ] |
The typename keyword is used in two different situations:
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When referring to a qualified member of a class template, the compiler cannot tell whether the name refers to a type, object, or function. Use typename before the qualified name to tell the compiler that it names a type.
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In a template declaration, use typename to name a type parameter. In this context, class means the same thing as typename .
Example
template< typename C> typename C::value_type checked_first(const C& c) { if (not c.empty( )) return c[0]; throw std::out_of_range("container is empty"); }
See Also
class , expression , template , type , using , Chapter 7