asked on

Using "using"

Why doesn't this compile? What's the correct
syntax for what I'm trying to do?

#include <iostream>

class A{
public:
operator float(void)const{return 0;}
};

class B{
public:
operator float(void)const{return 1;}
};

class C:
public A,public B
{
public:
using A::operator float(void)const;
};

int main(void)
{
C c;
cout<<float(c)<<endl;
}

//If there are any typos I'm sorry, I don't have
//cut and paste. Please concentrate on the "using"
//issue.

//Thanks

Axter

Try the following:

#include <iostream>

using namespace std;

Axter

Oops!
I didn't see the using A::

Using is for namespace.
In your code, A is not a namespace. It's a class.
So it would be improper to put using, and it would be improper to put the A there as well.

What exactly are you trying to do with the operator float(void)const?

Are you trying to over write it?

Axter

OK,
I think I see what you're trying to do.
Try the following:

class A{
public:
operator float(void)const{return 0;}
};

class B{
public:
operator float(void)const{return 1;}
};

class C:
public A,public B
{
public:
operator float(void)const
{
return A::operator float();
}
};

int main(void)
{
C c;
cout<<float(c)<<endl;
return 0;
}

Axter

Also try this.

class C: public A,public B
{
public:
using A::operator float;
};

I believe that is the right syntax for selecting a specific multi inherited function.

BUT!!!
I tried compiling this in VC, and it didn't work.
I think it's a VC bug, because the following does compile, and runs correctly.

class Z: public X,public Y
{
public:
using X::f;
};

int main(void)
{
Z z;
cout<<z.f()<<endl;

ASKER CERTIFIED SOLUTION

Axter

membership

This solution is only available to members.

To access this solution, you must be a member of Experts Exchange.

Start Free Trial

glebspy

ASKER

Thanks Axter, I'll try that stuff soon.

glebspy

ASKER

Thanks very much

jasonclarke

Just for information, I think it is almost certainly a VC++ bug; it compiles and runs just fine with g++.

Using &quot;using&quot;

Using "using"