Re: "template container" declaration error

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 12 Feb 2009 01:26:37 -0800 (PST)
Message-ID:
<212ec3a7-dada-4538-bdda-31ab567b9d76@h16g2000yqj.googlegroups.com>
On Feb 11, 6:10 pm, vl_ <vlyamt...@gmail.com> wrote:

I am trying to declare "containerr" class for the template, so
that it would contain explicit size for the templated object:

MyClass.hpp
#include <queue>
template <typename T>
// Container class
class Element
{
public:
        Element( T t, int size)
        {
                m_t = t;
                m_size = size;
        }
        virtual ~Element() {};
        T m_t;
        int m_size;
} ;

// Queue wrapper
template <typename T>
class MyQueue
...
//STL queue declaration:
std::queue <Element> m_queue;

....
I have the following error: "ISO C++ forbids declaration of
`m_queue' with no type,
  expected a type, got `Element'"

Why doesn't compiler see declaration of type 'Element' ?


The compiler can see the definition of Element. That's how it
knows that it's not a type. Otherwise, it would probably give
an error message along the lines of "unknown symbol".

A template is not a type. A class template is a specification
which can be instantiated to create a type, but only the
instantiations are types. You need something along the lines
of:
    std::queue< Element< T > > m_queue ;

--
James Kanze (GABI Software) email:james.kanze@gmail.com
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