dynamic_cast won't compile that I have to have at least one virtualmethod

[srdgame]

Below is my testing code, and it won't be compiled successfully, unless
you uncomment the "virtual void f(){}".

I wanna to know is this required by C++ Standard, or just because of GCC?

struct A
{
//virtual void f(){}
};
template <class T>
struct TA : public A
{
T _t;
};

int main()
{
A* a = new TA<int>();
TA<int>* ta = dynamic_cast< TA< int >* >(a);

delete a;
}

thanks
srdgame

 

[Ian Collins]

Below is my testing code, and it won't be compiled successfully, unless
you uncomment the "virtual void f(){}".

I wanna to know is this required by C++ Standard, or just because of GCC?

wanna?

dynamic_cast can only be used on polymorphic objects, so yes, at least
one virtual method is required.

 

[srdgame]

于 Sat, 21 Mar 2009 15:43:43 +1300，Ian Collins写到：

wanna?

dynamic_cast can only be used on polymorphic objects, so yes, at least
one virtual method is required.

Thanks for your reply. I have to give up to use dynamic_cast, and trun
to static_cast. What is pity!

srdgame

 

[SG]

Sat, 21 Mar 2009 15:43:43 +1300，Ian Collins：

Thanks for your reply.  I have to give up to use dynamic_cast, and trun
to static_cast.  What is pity!

You shouldn't. You NEED polymorphism here for the destructor.
Otherwise you get undefined behaviour ("delete a") because a is of
type A* but it points to an object of type TA<int>. You need to
write:

struct A
{
virtual ~A(){}
};

to make it work.

Cheers!
SG