-Woverloaded-virtual : why ?

-Woverloaded-virtual : why ?

[Matthew Jones]

Why does the following code generate an error ?
This error is described in the gcc manual under the C++ -Woverloaded-virtual
flag. I can't see why gcc can't generate a call to A::f(Y). This exactly
against the behaviour one would expect under the basic principles of
polymorphism.
(gcc 3.4.3).


struct X{};
struct Y{};
struct Z{};

struct A
{
    virtual void f(X);
    virtual void f(Y);
    virtual void f(Z);
};

struct B: public A
{
    virtual void f(X);
};

void Test (void)
{
    B b;
    X x;
    Y y;

    b.f(x);
    b.f(y);     // error: no matching function for call to 'B::f(Y&)'
}

--
Matthew JONES
http://www.tandbergtv.com/

Re: -Woverloaded-virtual : why ?

[Peter Doerfler]

Hi Matthew.

Take a look at
http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.7

You are hiding all A::f() by declaring a B::f().
'using' should help.

HTH, Peter 

On Thursday 18 August 2005 16:10, Matthew Jones wrote:
> Why does the following code generate an error ?
> This error is described in the gcc manual under the C++
> -Woverloaded-virtual flag. I can't see why gcc can't generate a call to
> A::f(Y). This exactly against the behaviour one would expect under the
> basic principles of polymorphism.
> (gcc 3.4.3).
>
>
> struct X{};
> struct Y{};
> struct Z{};
>
> struct A
> {
>     virtual void f(X);
>     virtual void f(Y);
>     virtual void f(Z);
> };
>
> struct B: public A
> {
>     virtual void f(X);
> };
>
> void Test (void)
> {
>     B b;
>     X x;
>     Y y;
>
>     b.f(x);
>     b.f(y);     // error: no matching function for call to 'B::f(Y&)'
> }
>
> --
> Matthew JONES
> http://www.tandbergtv.com/