Re: data corruption on pointer cast

 Old Wolf <>
Mon, 16 Jul 2007 15:34:21 -0700
On Jul 16, 5:56 pm, wrote:


template<class T>
class Element
        virtual int operator == (T) = 0;
        virtual int hash() = 0;

        int exists(Element<T> * elem)
                int h = elem->hash()%M;
                for (int i=0; i < size_t[h]; i++)

This is a syntax error -- size_t is a keyword,
you can't apply array indexing to it

                        if ( *((T*)elem) == *((T*)set[h][i]))

This line is wrong. 'elem' does not point to
a T, it points to a class with virtual functions.

The only way this could work is if 'elem' defined
an "operator T *" conversion operator, but it doesn't.

You should never use a C-style cast in C++, because
it will usually make the compiler suppress all the
warnings that you're doing something wrong.

I'm not sure what the code is meant to do, so I can't
suggest a replacement. Element<> contains no T and
no functions to access a T, so I don't see how you
are expecting to get a T out of it.

If Element<T>::operator== took another Element<T> as
the argument, then you could write:
  if ( *elem == set[h][i] )

As James Kanze pointed out, you're using far
too many pointers. You should be able to
rewrite this program to not use any pointers.

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