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steve yee
Guest
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 Posted: Tue Sep 12, 2006 9:10 am Post subject: is g++ wrong? |
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g++ can't compile this code:
#include <iostream>
using namespace std;
template <typename T>
class Outer
{
public:
class Base
{
protected:
int m_n;
};
class Derived : public Base
{
public:
Derived(int n)
{
m_n = n; // g++ says m_n undeclared
}
void print()
{
cout << m_n << endl;
}
};
};
int main(int argc, char *argv[])
{
Outer<int>::Derived(100).print();
return 0;
} |
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Salt_Peter
Guest
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| Posted: Tue Sep 12, 2006 9:10 am Post subject: Re: is g++ wrong? |
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steve yee wrote:
| Quote: | g++ can't compile this code:
#include <iostream
using namespace std;
template <typename T
class Outer
{
public:
class Base
{
protected:
int m_n;
};
class Derived : public Base
{
public:
Derived(int n)
{
m_n = n; // g++ says m_n undeclared
}
void print()
{
cout << m_n << endl;
}
};
};
int main(int argc, char *argv[])
{
Outer<int>::Derived(100).print();
return 0;
}
|
You can't ask a compiler to guess what its suppose to do with that
template parameter. At the very least, a templated class will require a
ctor. There is also the fundamental question of what that "Outer" class
is suppose to bring to this design.
Maybe i'm wrong but you are attempting to solve a technical issue when
what i see is lack of a more fundamental startegy.
#include <iostream>
namespace Outer
{
template< typename T >
class Base
{
T m_t;
public:
Base() : m_t(0) { }
Base(T t) : m_t(t) { }
~Base() { }
T get() const { return m_t; }
};
template< typename T >
class Derived : public Base< T >
{
public:
Derived() { }
Derived(T t) : Base< T >(t) { }
~Derived() { }
void display() const { std::cout << Base< T >::get() <<
std::endl; }
};
} // namespace
int main()
{
Outer::Derived< int > d0;
Outer::Derived< int > d1(100);
d0.display();
d1.display();
return 0;
} |
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Jens Theisen
Guest
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| Posted: Tue Sep 12, 2006 9:10 am Post subject: Re: is g++ wrong? |
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Hi Steve,
g++ probably is right. Qualifying as m_n does satisfy it. Comeau also
agrees with g++. One could argue that In the context of Outer, Base
isn't dependent on a template (as none of the other members are) and
so m_n should be found unqualified, but that doesn't appear to be how
it's generally implemented.
Does anyone know the relevant passages in the standard?
Jens |
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