Difference of keywords 'typename' and 'class' in templates?

Question

For templates I have seen both declarations: template < typename T > template < class T > What's the difference? And what exactly do those keywords mean in the following example (taken from the German Wikipedia article about templates)? template < template < typename, typename > class Container, typename Type > class Example { Container< Type, std::allocator < Type > > baz; };

Answer 1

There is no difference between using <typename T> vs. <class T>; i.e. it is a convention used by C++ programmers. I myself prefer <typename T> as it more clearly describes it use; i.e. defining a template with a specific type :)

Note: There is one exception where you do have to use class (and not typename) when declaring a template template parameter:

template <template <typename> class T> class C { }; // valid!

template <template <typename> typename T> class C { }; // invalid!

In most cases, you will not be defining a nested template definition, so either definition will work -- just be consistent in your use...

I hope this helps.