C++ Iterator with hasNext and Next - c++

Question

I am new to C++ world and I need a help. My problem is I try implement my structure hash pair array, there is key and data. In this structure I have nested structure iterator with methods hasNext and next. Because I can not see my array (this array is in parent) from nested structure I need pass it through constructor, but there is error ": cannot convert from...", problem is with pass _array in method getIterator. Code is below. Could you help me? Thanks
#pragma once
template<typename T, typename U, int Size, int(*HashFunction)(T)>
struct HashPairPole {
// Pair - key - data
struct Par {
// key
T _first;
// data
U _second;
// list for collision records
Par* _overflow;
Par(T t, U u) {
_first = t;
_second = u;
_overflow = nullptr;
}
};
HashParovePole() {}
// Static array for save data
Par* _array[Size];
// Add record into hash table
void add(T t, U u) {
// calculating of index
Par* prvek;
int idx = HashFunction(t) % Size;
// Element will be saved in _array[idx], if it is free, else will be
//saved to list (->_overflow)
prvek = new Par(t, u);
if (_array[idx] == nullptr) {
_array[idx] = prvek;
}
else {
prvek->_overflow = _array[idx];
}
_array[idx] = prvek;
}
// Get data from hash tabule
U& get(T t) {
int idx = HashFunction(t) % Size;
Par * prvni = _array[idx];
while (prvni->_overflow != nullptr) {
if (prvni->_first == t) {
return prvni->_second;
}
prvni = prvni->_overflow;
}
}
U& operator[](T t) {
return get(t);
}
U operator[](T t) const {
const U temp = get(t);
return temp;
}
// Iterator for walking all hash table
struct iterator {
Par* index[Size];
Par* pomPar;
int temp = 0;
iterator(Par * _array) {
index = _array;
pomPar = index[0];
}
bool hasNext()const {
return pomPar != nullptr;
}
std::pair<T, U> next() {
std::pair<T, U> data;
if (hasNext()) {
data.first = pomPar->_first;
data.second = pomPar->_second;
pomPar = pomPar->_overflow;
}
temp++;
pomPar = index[temp];
return data;
}
};
// Vytvori iterator
iterator getIterator() {
return iterator(_array);
}
};

Answer 1

As far as I see, the problem is in this line:
Par* _array[Size];
Here you declare an array of size Size of pointers to Par structures, which is probably not what you want.
Later you try to pass this array to constructor iterator(Par * _array), which accepts a pointer to Par structure, which is impossible.
I would fix this code in the following way:
Par _array[Size]; // Instead of Par* _array[Size]
// You need an array of structures instead of array of pointers
...
Par* index; // Instead of Par* index[Size]
// Here looks like index is a pointer to a current element
...
pomPar = index; // Instead of pomPar = index[0];
// This is a pointer to the node, while index[0] is its value
Also, consider using std::vector instead of raw pointers. It will handle memory management issues for you.