Templated classes with nested classes

[card]

Hi everyone,

I have a question about referencing a nested class contained within a templated class. Of course the best way to show you is by example. Here's my templated classes:

#include <stack>
 
template <class T>
class A
{
public:
 
    // constructor
    A(const T &zz): z(zz) {}
    T z;
 
    // nested class
    class B
    {
    public:
        // constructor
        B(const T &xx, const T &yy): x(xx), y(yy) {}
        T x;
        T y;
    };
};
 
template <class T>
class Iter
{
public:
    Iter(const T &xx): x(xx) {}
    T x;
 
    std::stack< A<T> > aStack;
    std::stack< A<T>::B > bStack;
};
 
 

As you can see, class A is a templated class and class B is nested within A. I have another templated class called Iter. Within Iter, I have two stacks. One contains objects of A and the other objects of the nested class B contained in A. A simple main program to build the code is below:

#include "nested.H"
 
int main(int argc, char *argv[])
{
    A<int> myAObject(5);
    A<int>::B myBOjbect(6,7);
    Iter<int> myIterObject(2);
 
    return 0;
}
 

The build with g++ fails with the following error:

nested.H:44: error: type/value mismatch at argument 1 in template parameter list for ‘template<cla\
ss _Tp, class _Sequence> class std::stack’
nested.H:44: error: expected a type, got ‘A<T>::B’
nested.H:44: error: template argument 2 is invalid

As you can see, it doesn't know what to do with A<T>::B in the stack declaration of the templated class Iter. How do I reference this nested class within Iter? Obviously, I can do it in main as shown above. Many thanks.

-David

[boxfish]

Try changing
std::stack< A<T>::B > bStack;
to
std::stack< typename A<T>::B > bStack;
Somehow that lets the compiler know A<T>::B is a type, but I have no idea why you have to do it. Template syntax-
AAAAAAAAAAAAARRRRRRRRRRGGGH!!
Good luck.

[card]

Try changing
std::stack< A<T>::B > bStack;
to
std::stack< typename A<T>::B > bStack;
Somehow that lets the compiler know A<T>::B is a type, but I have no idea why you have to do it. Template syntax-
AAAAAAAAAAAAARRRRRRRRRRGGGH!!
Good luck.

Thanks boxfish! I've been pulling my hair out for a couple hours. That did the trick.