Question

I am struggling with the syntax needed to declare, create, and manipulate a pointer to an array of list objects. I’m creating a hash table template class for a course assignment, using chaining to deal with has collisions.

The way my hash table is supposed to be is an array of list objects. std::list is the only standard library data class I’m allowed to use for the assignment, so vector is out.

My questions are:
How do I declare a pointer to an array of std::list? I have:

private:
    std::list<T> * table;

How do I create the array? I have:

table = new std::list<T>[3]; // start with table size 3

I think I have the declaration and construction right, but I’m not 100% sure. Lastly, how do I interact with the list’s? I’ve got:

    for (int i = 0; i < _tableSize; i++) { // _tableSize is the array's size
        if (!table[0][i].empty()) {
            table[0][i].push_back(thing);
        }
    }

Somehow table[0][i] seems wrong to access a cell of the array that table points to. What should it look like?

Answer 1

Since table is a std::list*, table[i][j] means (table + i)->operator[](j); that is, it calls a member function (with argument j) on the std::list object starting at address table + i.

It follows that, since std::list doesn’t overload [], table[0][i].empty() is wrong (doubly wrong if T in std::list<T> is such that it hasn’t a member function empty).

Shortly, I think that what you need is a simple table[list_index_on_array].empty() to check for emptiness.

Everything else looks ok.