Re: Templating classes

From:
"Victor Bazarov" <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Fri, 1 Jun 2007 17:46:12 -0400
Message-ID:
<f3q435$t0a$1@news.datemas.de>
MathStuf wrote:

On Jun 1, 5:11 pm, red floyd <no.s...@here.dude> wrote:

MathStuf wrote:

[redacted]

Hmm...guess I should have looked exactly where it was getting mixed
up there. It's in the following code:

template<class T> class Matrix : public MatrixBase<T>
{
   public:
      Matrix()
      {
         width = 0;
         height = 0;
         matrix.clear();
      }
      // More methods
};


Note that since width and height are members of MatrixBase<>, it's
probably better to let MatrixBase set them. If you need something
other than what MatrixBase has set as the "default", MatrixBase
should have a constructor with width and height parameters.


Alright, but I still have problems with their availability. I have
GetWidth() and GetHeight() methods in MatrixBase<>, but when i go to
call it, the compiler complains about it.

\Matrix.h:161: error: there are no arguments to `GetHeight' that
depend on a template parameter, so a declaration of `GetHeight' must
be available


That's just not true. 'GetHeight' is non-static, so it *does* have
one argument that depends on the template argument - the instance of
the class (the object). But it doesn't really matter. The full name
of 'GetHeight' is 'MatrixBase<T>::GetHeight', which means it *does*
depend on 'T' (simply because it is a member of the template).

I'm confused since MatrixBase<T> is inherited as public, and protected
members should be available (as well as public ones such as
GetHeight() and GetWidth()). I have other classes (non-template
though)


That's *the* difference.

where an id is inherited from the base class (public
inheritance of a protected variable) and straight calls to the id
works. Do templates mess with inheritance at all?


No, but they do have slightly different rules for name lookup.

I don't think they
would, but that's what it would seem is happening here.


No, you just need to learn name lookup rules.

V
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