Question

While browsing the standard I found some syntax in the template declaration that confused me:

template <typename T> class myarray;

template </*...*/, template <typename T> class C = myarray>

What does class C = myarray mean? Is it a default parameter? Thanks.

Answer 1

It’s a default value for the template template argument. If you don’t specify the argument, it will default to myarray.

Example:

template <typename> class Foo;
template <typename> class Bar;

template <typename T, template <typename> class C = Foo>
class Zip
{
    typedef C<T> type;  // example use of "C"
    // ...
};

Zip<int, Bar> x;  // OK
Zip<int>      y;  // OK, y has type Zip<int, Foo>