Re: data corruption on pointer cast

=?ISO-8859-1?Q?Erik_Wikstr=F6m?= <>
Mon, 16 Jul 2007 08:00:04 GMT
On 2007-07-16 07:56, wrote:


Names matt,

I implemented a set class as follows:

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

virtual bool operator==(const T&) = 0;

     virtual int hash() = 0;

 * A efficient hash implementation of a Queue-set that does not allow
addition of duplicates.
    @author matt gara <>
template<class T, int M = p>
  class QueueSet


    int exists(Element<T> * elem)
        int h = elem->hash()%M;
        for (int i=0; i < size_t[h]; i++)
            if ( *((T*)elem) == *((T*)set[h][i]))
                return 1;
        return 0;

    int add(Element<T> * elem)
        int h = elem->hash()%M;
        if (size_t[h] == max[h])
            set[h] = (Element<T> **)realloc(set[h], sizeof(Element<T>
*)*(max[h] + P));

Unfortunately I don't think that there's any guarantee that realloc will
work on anything except POD types, which makes it very dangerous to use
in C++.

             max[h] += P;
        if (exists(elem))
            return 0; //failed to add
        set[h][size_t[h]] = elem;
        size_t[h] += 1;
        return 1;



    Element<T> ** set[M];
    int size;
    int size_t[M];

size_t is the name of a type used extensively throughout the standard
library, using it as an identifier might not be a good idea.

     int max[M];

Sorry, can't help you with your problem, I can only point out some other
things in your code. One thing I noticed was that you use an awful lot
of pointers, try using references instead. Also you might want to make
Element a private class to QueueSet and make it's use transparent to the
user, require instead that the elements are comparable and let the user
supply the hash-function as a template parameter:

   template<class T, class H, int M = p>
     class QueueSet { ... };

where H is the hash-function.

Erik Wikstr?m

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