another c++ cast question

Code:

class base {
public:
	char m;
}

class derived : public base {
public:
	char c;
}

void somefunc(base **bc) { }

int main() {
	derived *ptr = 0;
	somefunc(reinterpret_cast<base**>(&ptr));
	return 0;
}

Is this a right way to do it in C++?
Normally I would just do somefunc((base**)&ptr); and it would work just fine..
I tried dynamic_cast but it didnt work.

That might work, but what is somefunc() supposed to do? There might be a better way of doing it.

Somefunc is just an 'interface' for WinAPI function, so that I dont have specify all arguments each time I call it (I can save lines).

Shouldn't I do this kind of casts with dynamic_cast?

Can you not write it as:

Code:

void somefunc(base* bc) { /* ... */ }

If so, all you need is to pass the derived pointer, no casting would be needed.

The code is very dangerous. It suggests that somefunc will assign a value to the pointer, such as this:

Code:

void somefunc(base **bp)
{
  *bp = new derived;
}

This way, after somefunc returns, ptr points to a derived object. So far, so fine. But look, this is also perfectly valid for somefunc to do:

Code:

void somefunc(base **bp)
{
  *bp = new base;
}

It's just a pointer to base, so you can assign the address of a base object to it, right? Or any object derived from base, perhaps other_derived.

On the other hand, if you do that, suddenly ptr points not to a derived, but a base or an other_derived. Welcome to the land of hidden bugs.

In other words, while casting a pointer to a derived class to a pointer to a base class is perfectly safe and can be done implicitly, casting a pointer to a pointer to a derivd class to a pointer to a pointer to a base class is a big no-no.

Ok, this is how I have changed it:

Code:

void somefunc(base *&bc) {
	//I reinterpret cast it here before I pass it to WinAPI
}

int main() {
	derived *ptr = 0;
	somefunc(ptr);
	return 0;
}

Did you mean this?
Is there any other way to do this?

Thanks for help again

BTW, laserlight is that girl on avatar you?