Visual Studio C++ Runtime Error: Exception thrown: read access violation. _Pnext was 0xDDDDDDE1

Question

I am working on a homework assignment where we are supposed to implement a set using a hash based chain implementation.

We are using C++'s forward_list for the buckets.

We have to overload operators + for union, * for intersection, and the assignment operator (=). But every time I run my program, I get this error.

Exception thrown: read access violation.
_Pnext was 0xDDDDDDE1.

This code gives me the error. Specifically the last line

SetT<int> setA;
SetT<int> setB;
SetT<int> setResult;

setA.Add(20);
setB.Add(20);
setResult = setA * setB;

I tried debugging, but it didn't help. It would go through the operator* with no problems, then it would go through the operator=, exit, and then as soon as I got back to main to go to the next line, it would give me the error.

I also looked similar questions, but I wasn't able to find the reason why my program crashes.

These are the private variables for the class SetT

forward_list<T>** buckets;  // An array of forward_list's 
                                // (ie, each index is a forward_list pointer)
    int numBuckets;
    int getHashIndex(const T& elem);
    int numElems;

    // Iterator variables
    int currBucket;                                         // what bucket is the iterator on?
    mutable typename forward_list<T>::iterator bucketIter;  // the iterator of the current bucket

This is the code for Add:

template<class T>
bool SetT<T>::Add(T elem)
{
    // If the set already contains elem, do nothing
    if (Contains(elem)) {
        return false;
    }

    // Get the bucket index and add the element to the bucket.
    currBucket = getHashIndex(elem);
    buckets[currBucket]->push_front(elem);
    numElems++;
    return true;

    // Extra credit:  If the load factor becomes too large, change the number of buckets and rehash.
}

The hashing function was given by our professor, and he told us not to touch it.

This is the code for Contains:

template<class T>
bool SetT<T>::Contains(T elem)
{
    // Use hash function to find the bucket, then check
    // to see if elem is in the bucket.
    currBucket = getHashIndex(elem);

    for (bucketIter = buckets[currBucket]->begin(); bucketIter != buckets[currBucket]->end(); ++bucketIter) {
        if (elem == *bucketIter) {
            return true;
        }
    }

    return false;
}

And this is the code for the operators

template<class T>
SetT<T> SetT<T>::operator*(SetT& other)
{
    SetT<T> result;

    // Your code here
    // This function should return the Intersection between "this" and otherSet.
    // It should NOT change "this" or otherSet
    for (int i = 0; i < numBuckets; i++) {
        for (bucketIter = buckets[i]->begin(); bucketIter != buckets[i]->end(); ++bucketIter) {
            T value = *bucketIter;
            if (Contains(value) && other.Contains(value)) {
                result.Add(value);
            }
        }
    }

    return result;
}

template<class T>
SetT<T> SetT<T>::operator=(const SetT& other)
{
    if (other.numElems == 0) {
        return SetT<T>();
    }

    else {
        return other;
    }
}

Does anyone know what is causing this error?

Thanks.

Edit: This is the professor's hash function

template<class T>
int SetT<T>::getHashIndex(const T& key)
{
    // This is done... No touching!
    unordered_map<int, T> mapper;
    typename unordered_map<int, T>::hasher hashFunction = mapper.hash_function();
    return static_cast<int>(hashFunction(key) % numBuckets);
}