How can a template class use the types in another template class in C++?

Question

I have a template class that depends on another template class. How can TemplateClassB use the type TypeA of TemplateClassA?

template <int L>
class TemplateClassA {
public:
  typedef unsigned TypeA;
};

template <typename E, typename F>
class TemplateClassB {
  TemplateClassA::TypeA var;   //error: invalid use of template-name 'TemplateClassA' without an argument list
}; 

int main(){
  TemplateClassA<1> A = TemplateClassA<1>();
}

You need to specify a template parameter for `TemplateClassA` in the declaration of `var`, and also use `typename` — Brian Bi, Mar 18 '14 at 22:34
Please call them "class templates". They are templates that make classes, not a funny kind of class. — Lightness Races in Orbit, Mar 18 '14 at 23:12
possible duplicate of [Where and why do I have to put the "template" and "typename" keywords?](http://stackoverflow.com/questions/610245/where-and-why-do-i-have-to-put-the-template-and-typename-keywords) — Constructor, Mar 19 '14 at 07:19

score 2 · Accepted Answer · answered Mar 18 '14 at 23:35

2

As Brian says, use

typename TemplateClassA<L>::TypeA var;

where L is some int.

answered Mar 18 '14 at 23:35

iavr

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if L is not known beforehand, then TemplateClassB has to have another template parameter, L, is that correct? – Pippi Mar 19 '14 at 00:00
yes, you'd have template class TemplateClassB { – thisisdog Mar 19 '14 at 01:08

How can a template class use the types in another template class in C++?

1 Answers1