Re: derived class access to virtual base class variables?

From:

red floyd <no.spam@here.dude>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 8 Nov 2007 19:30:17 CST

Message-ID:

<BrNYi.4243$yV6.1229@newssvr25.news.prodigy.net>

Alexandru wrote:

Why do I get an error when trying to access x from Inner1 and Inner2?

Your subject is incorrect. It's templates, not virtual base class.

Specifically, your question is answered in FAQ 35.19:

http://www.parashift.com/c++-faq-lite/templates.html#faq-35.19

Essentially, x is a dependent name, so the compiler needs help in
knowing it's a member variable. Either use this->x, or Data<U>::x.

#include <cstdio>

template<class T> class Data {
public:
    int x;
};

template<class U> class Inner1: virtual public Data<U> {
public:
    void operator () () {
        printf("nespecializat1\n");
        x = 3;
    }
};

template<class U> class Inner2: virtual public Data<U> {
public:
    void operator () () {
        printf("nespecializat2\n");
        x = 5;
    }
};

template<class T> class Base: virtual public Data<T>, public
Inner1<T>, public Inner2<T> {
public:
    Inner1<T> a;
    Inner2<T> b;
};

int main() {
    Base<char> x;
    x.a();
    printf("%d\n", x.x);
    x.b();
    printf("%d\n", x.x);

    return 0;
}

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