Re: Problem with inheritance of classes with template parameter

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Mon, 6 Aug 2007 10:50:01 -0400

Message-ID:

<f97ceo$9lj$1@news.datemas.de>

Thomas Witkowski wrote:

I have a class with one template parameter. When a second class, also
with a template parameter that is forwarded to the first class, is
derived from this class, why it is required to enter the variables of
the first class with this-> ?

Because such are the rules of the language. The name lookup is only
performed in the non-dependent [temp.dep]/3 base classes.

Here a small example:

template<typename T>
class Class1
{
public:
bool testvar;
};

template<typename T>
class Class2 : public Class1<T>
{
public:
void test123() {
this->testvar = false;
}
};

If I delete this->, so I would just write testvar = false, it does not
work. The compiler (gcc (GCC) 4.1.1 20070105 (Red Hat 4.1.1-52))
returns the error that testvar is not in the current scope. Can
somebody explain it to me?

I am not sure what to explain. You have to tell the compiler that the
name you're using ('testvar') is a member. Since that name is not found
in the 'Class2' itself, the compiler cannot assume whether you meant to
use the member from the base class or a global object (if the base class
does not have such a member, which is easily achieved with a "custom"
specialisation of 'Class1' template).

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask