Question

Let’s say I’m using a templated class with something simple like:

template <class T> 
class MyClass

I want to use elements from T’s namespace, for example T could be string, and I wanted to use

T::const_iterator myIterator; 

…or something like that. How do I achieve that?
Probably, it’s either not possible or very simple, but I have no idea.

Thanks for answers!

Answer 1

By default if T is a template parameter like in your example, the T::some_member is assumed not to name a type. You have to explicitly specify that it is, by prefixing it with typename:

typename T::const_iterator myIterator;

This resolves some parsing problems like in the following example

// multiplication, or declaration of a pointer?
T::const_iterator * myIterator;

So that the compiler can parse this even before instantiating the template, you have to give it a hand and use typename, including in those cases where it wouldn’t be ambiguous, like in the first case above. The Template FAQ has more insight into this.