Re: The following code causes an infinite loop. Can you spot the
problem and explain why?
On Nov 23, 6:42 am, onLINES <dopeli...@gmail.com> wrote:
On Nov 23, 12:33 am, "doublemaster...@gmail.com"
<doublemaster...@gmail.com> wrote:
class Base
{
public:
Base() {}
virtual void func() { /* do something */ }
};
class Derived : public Base
{
public:
Derived() {}
virtual void func()
{
Base:func();
/* do something else */
}
};
int main()
{
Derived d;
d.func(); // Never returns!
}
Yes it does.
No it doesn't. It terminates with stack overflow (formally,
undefined behavior, but a core dump or the equivalent on most
general purpose machines).
It's syntactically incorrect (moreso, hard to understand) as
to why you'd have virtual function within the base class, when
the base class has the same name.
I'm having problems parsing that statement. The base class has
the same name as what? But the program is definitely
syntactically correct.
The compiler (bad one) would not know what to do since both
are virtual, and both contain the same name along with method
parameters.
If you're talking about the function func() (which I suppose
because that's the only thing which has two declarations), his
code is a perfectly classical example of how to implement a
polymorphic class in C++. He defines a virtual function in the
base class, and overrides it in the derived class.
However, it does return. And it exists successfully.
Did you actually try it? (A good compiler will warn about an
unreferenced label, but the language itself doesn't require
labels to be referenced.)
Program execution is as follows.
Derived Constructor is called, return to last calling point :
Somewhere before the body of the constructor of Derived is
entered, the constructor of Base will have been called. But in
the end, yes, the object gets constructed, and we return in
sequence.
Main
Call constructed class, d.
You call a function, not a class. Next, we call Derived::func.
Jumps into class Derived : Name is the same as base class
Goes into the called method within Derived.
Calls Base class
Where does it do that? His code never calls Base::func.
Derived::func calls itself recursively. (Note that for
Derived::func to call Base::func, he would have to have written
Base::func, and not Base:func.)
--
James Kanze (GABI Software) email:james.kanze@gmail.com
Conseils en informatique orient=E9e objet/
Beratung in objektorientierter Datenverarbeitung
9 place S=E9mard, 78210 St.-Cyr-l'=C9cole, France, +33 (0)1 30 23 00 34