Officially, what is typename for?

Question

On occasion I\'ve seen some really indecipherable error messages spit out by gcc when using templates... Specifically, I\'ve had problems where seemingly correc

Answer 1

Consider the code

template somefunction( T * arg )
{
    T::sometype x; // broken
    .
    .

Unfortunately, the compiler is not required to be psychic, and doesn't know whether T::sometype will end up referring to a type name or a static member of T. So, one uses typename to tell it:

template somefunction( T * arg )
{
    typename T::sometype x; // works!
    .
    .