Question

This code crashes when I call extractMin() more than once. I think it should be obvious to
some of you where the problem lies in the function since I am new to pointers and is probably an obvious bug. So it should be enough that you know it´s a linked list without going into detail other than the function is supposed to retrieve the lexicographical smallest value using the < operator, and then delete that value from the linked list.

string LinkedListPQueue::extractMin() {
    if (this->isEmpty()) throw ErrorException("Empty queue.");
    string front = LEX_HIGH;
    cell *old;

    for (int i = 0; i < this->size(); i++) {
        if (this->head->value < front) {
            front = this->head->value;
            old = this->head;
        }

        old = this->head;
        this->head = this->head->next;
    }

    logSize--;
    delete old;
    return front;
}



void LinkedListPQueue::enqueue(const string& elem) {
    cell *newCell = new cell;
    newCell->value = elem;
    newCell->next = NULL;
    if(this->isEmpty()) {
        this->head = this->tail = newCell;
        logSize++;

    } else {
        recurSort(newCell);
        this->tail->next = newCell;
        this->tail = newCell;
        logSize++;
    }
}

Answer 1

You are modifying the head member in extractMin(), which leaves the list broken.