Re: 'Undefined' error

From:

Victor Bazarov <v.bazarov@comcast.invalid>

Newsgroups:

comp.lang.c++

Date:

Tue, 17 Jul 2012 11:08:17 -0400

Message-ID:

<ju3v52$59h$1@dont-email.me>

On 7/17/2012 10:33 AM, Peter Davis wrote:

I'm trying to define a template class ...

namespace abc
{
     class Node;
     typedef boost::shared_ptr<Node> NodePtr;
     template <typename Derived> class Cloneable
     {
     public:
         virtual NodePtr clone() const
             {
                 Derived *d = new Derived(static_cast<const
Derived&>(*this));
                 return d->makeNodePtr(); }
     };
...

and then use that as a superclass of another class ...

#include "abc/dom/Node.hpp" // The file above!
namespace abc
{

     class Node : public BaseObject, Cloneable<Node>
     {
...

This follows, as I understand it, the 'curiously recurring template'
pattern. However, when I try to compile (Visual Studio 2008), I get the
error:
C2504: 'CloneableImpl' : base class undefined.
on the line defining class Node. I don't understand why, since the cpp
file includes the header file in which the template Cloneable is
defined, and they're in the same namespace.

Any insights?

Not with your incomplete code. See FAQ 5.8.

This code:
--------------------------------------------------
namespace abc
{
    class Node;
    typedef Node* NodePtr;
    template <typename Derived> class Cloneable
    {
    public:
       virtual NodePtr clone() const
       {
          Derived *d = new Derived(static_cast<const Derived&>(*this));
          return d->makeNodePtr();
       }
    };

    class BaseObject
    {

    };
}

namespace abc
{
    class Node : public BaseObject, Cloneable<Node>
    {
    public:
       Node* makeNodePtr() { return new Node; }
    };
}

int main()
{
    abc::Node blah;
    abc::Node* blahblah = blah.makeNodePtr();
}
--------------------------------------------------
compiles fine with VC++ 2010. I don't have 2008 to test.

V
--
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