template inheritance when base's members initialize derived members

[StudentFS]

Hi!
The question is about template inheritance when base's members are supposed to initialize the derived members. The following code works fine but if one removes comments it returns an error. The problem, as far as i understand, is that the template does not generate actual type at definition, therefore members of the base template cannot initialize members of the derived template. Is there some beautiful solution for this problem?

/*template <int dim>*/ class A {
protected:
     int A_a;
public:
     A (int arg) : A_a(arg) {}
};

/*template <int dim>*/ class B : public A/*<dim>*/ {
protected:
     int B_b;
public:
     B (int arg) : B_b(A_a), A/*<dim>*/(arg) {}
};

int main () {
B/*<2>*/ x(3);
}

[Paul McKenzie]

1) Get rid of the comments and other extraneous characters
2) Post your code using code tags so that it becomes readable.

Regards,

Paul McKenzie

[StudentFS]

Thanks, done. Comments in the code are significant for the question.

[Paul McKenzie]

As to the answer to your question, this code compiles correctly. Note the changes made in red:

template <int dim> 
class A {
protected:
     int A_a;
public:
     A (int arg) : A_a(arg) {}
};

template <int dim> 
class B : public A<dim> 
{
protected:
     int B_b;
public:
     B (int arg) : B_b(this->A_a), A<dim>(arg) {}
};

int main () {
B<2> x(3);
}

There are two solutions, and one is what I gave above. Here is the pertinent link as to why this works:

http://www.parashift.com/c++-faq-lit...html#faq-35.18
http://www.parashift.com/c++-faq-lit...html#faq-35.19

Regards,

Paul McKenzie

[StudentFS]

That's great! Thank you very much!

[Peter_APIIT]

AFAIK, inheritance is off by default for template. In other words, function name in base class is hided in derived class. There are several solution to this. Why is point of this program ?

1. using directive.
2. Explicit qualified name.
3. this pointer
I think(guess) this pointer only applicable to Is-a relationship.

Thanks for your help.

[StudentFS]

Thank you for answer.