BST with function ptr, How to add in extra argument? - c++

Question

is there a way to pass in an extra argument to my function pointer in BST? I am trying to use BST inOrder to get value from a map<string, int>. this BST will be storing the key of the map.
The map will act as a database that uses date + time as the key. each BST will be created to store the date+time of each year and saved into another map (bstMap) which holds all bst. bstMap will use the year as key.
BST inOrder with function ptr.
#ifndef BST_H
#define BST_H
#include<iostream>
using namespace std;
template <class T>
class Node.
{
public:
T m_key;
Node<T> *m_left;
Node<T> *m_right;
};
template <class T>
class BST
{
typedef void(*funcPtr)(T &);
public:
BST();
void Insert(T key);
void Delete();
void InOrder(void(*funcPtr)(T &)) const;
void PreOrder(void(*funcPtr)(T &)) const;
bool Search(T key);
T MaxValue();
bool IsEmpty() const {return m_root == nullptr;}
void DeleteTree();
private:
Node<T> *m_root;
protected:
Node<T> *Insert(Node<T>* node, T key);
Node<T> *Search(Node<T>* node, T key);
void InOrder(Node<T>* node, void (*funcPtr)(T &)) const;
void PreOrder(Node<T>* node, void (*funcPtr)(T &)) const;
void DeleteTree(Node<T>* node);
Node<T>* MaxValue(Node<T>* node);
};
template<class T>
BST<T>::BST(){
m_root = nullptr;
}
template<class T>
void BST<T>::InOrder(Node<T>* node, void(*funcPtr)(T &)) const
{
if (node != nullptr)
{
InOrder(node-> m_left, funcPtr); //recursive call for node left
funcPtr(node-> m_key);
InOrder(node->m_right, funcPtr);
}
}
template<class T>
void BST<T>::InOrder(void(*funcPtr)(T &)){
InOrder(m_root, funcPtr);
}
This line of code is called from main.cpp which pass the user input year into the map to return the bst which stores all relevant keys.
void GetData(string& year, map<string, BST<string>>& bstMap)
{
BST<string> bstKey = bstMap[year];
bstKey.InOrder(&GetTotal);
}
So here is where i am stuck..
void GetTotal(string& key) <- how do i reference my database map here?
{
cout<< key <<endl;
}

Answer 1

If you want to access variables outside of the BST template class (such as the map), then I advise changing your template to the following (assuming that m_root is a member variable of BST<T>, and that it is the root of tree):
template<class T, class Fn>
void BST<T>::InOrder(Fn funcPtr) const
{
InOrder(m_root, fn);
}
template<class T, class Fn>
void BST<T>::InOrder(Node<T>* node, Fn funcPtr) const
{
if (node)
{
InOrder(node-> m_left, funcPtr); //recursive call for node left
funcPtr(node-> m_key);
InOrder(node->m_right, funcPtr);
}
}
Then this way, you can pass a function object or lambda that knows about the map. In the case below, a lambda function is used:
void GetData(string& year, map<string, BST<string>>& bstMap)
{
BST<string> bstKey = bstMap[year];
bstKey.InOrder([&](std::string& key) { std::cout << bstMap[key] << "\n"; });
}
The above provides a lambda that captures the passed-in map parameter.