Re: Parent class still callable after deletion

From:

itaj sherman <itajsherman@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 10 Feb 2011 08:52:05 -0800 (PST)

Message-ID:

<41d5d1cf-a76e-4b33-8bf1-9c5e166182c3@o10g2000vbg.googlegroups.com>

On Feb 9, 4:30 pm, Olumide <50...@web.de> wrote:

Hi,

I've been trying to figure out why the following bit of code does not
crash and still outputs the "Hello son" message althought its been
explicitly deleted. (BTW, I'm using the gcc 4.3.4 compiler.)

Thanks,

- Olumide

/////////////////////////////////////////////////////////////////////////=

/////////////

    #include <iostream>

    class Parent
    {
    public:
        void speak()
        {
                std::cout << "Hello son" << std::endl;
        }
    };

    class Child
    {
    public:
        Child(Parent* _p ) : m_parent( _p )
        {

        }

        void speakToParent()
        {
                std::cout << m_parent << ":: " << this <<=

std::endl;

                m_parent->speak();
        }

    private:
        Parent* m_parent;

    };

    int main()
    {
        Parent *p = new Parent();
        Child *c = new Child( p );
        delete p;
        c->speakToParent();
        return 0;
    }

As they said, it is undefined behaviour.
Nevertheless, some compilers (i dont know gcc) have nice debugging
features, so that when you compile for debug version and execute, the
debugger will break and tell you when you reach undefined behaviour in
some situations when possible (certainly this one is possible).
I would expect release compilation (optimized) not to do such things,
as trying to check for such runtime errors will slow execution.

itaj