Apple

Hi, all

I accidentally encountered the following code (not exactly of course that is very simplified version)

class V {

virtual int getID() = 0;

};

class A : public V {

public:

virtual int getID(){return 0;}

virtual int getIDA(){return 10;}

};

class B : public V {

public:

virtual int getID(){return 1;}

virtual int getIDB(){return 11;}

};

A *a = new A();

B *b = new B();

void *getA() {

return a;

}

void *getB() {

return b;

}

int main (int argc, char * const argv[]) {

A *sa = static_cast<A *>(getB());

A *aa = dynamic_cast<A *>(sa);

//here aa ISN'T NULL!!!!!

return 0;

}

in that fragment

aa isn't null

I'd expect NULL, of course

NOTE: gdb clearly shows that aa (or sa) is an instance of the B class (with set print object on and set print vtbl on)

(gdb) p aa

$2 = (B *) 0x106940

(gdb) p *aa

$3 = (B) {

<V> = {

_vptr$V = 0x2078

}, <No data fields>}

(gdb)

from other hand

the following code behaves just fine

int main (int argc, char * const argv[]) {

V *v = static_cast<V *>(getB());

A *aa = dynamic_cast<A *>(v);

//here aa IS NULL which is good

return 0;

}

thanks in advance for any help with clarification