Binary tree (reading from file) - c++

Question

#include <iostream>
#include <string>
#include <fstream>
using namespace std;
template <class T>
struct TreeNode{
string value;
T key;
TreeNode<T> *LeftChild;
TreeNode<T> *RightChild;
TreeNode (T k,string Val)
{
this->value=Val;
this->key=k;
this->LeftChild=NULL;
this->RightChild=NULL;
}
};
template <class T>
class BinaryTree{
private:
TreeNode<T> *Root;
public:
BinaryTree();
void insertNode();
};
template <class T>
BinaryTree<T>::BinaryTree()
{
Root=NULL;
ifstream fin;
fin.open("names.txt");
string buffer;
T buff;
while (!fin.eof())
{
getline(fin,buffer,'~');
fin>>buff;
cout<<buff<<buffer<<endl;
cout<<"down the tree"<<endl;
TreeNode<T> *temp=Root;
while (temp!=NULL)
{
TreeNode<T> *Right=temp->RightChild;
TreeNode<T> *Left=temp->LeftChild;
if (temp->key>buff)
{
temp=temp->LeftChild;
}
else if (temp->key<buff)
temp=temp->RightChild;
}
cout<<"further down"<<endl;
}
temp->value=buffer;
temp->key=buff;
cout<<"and done!"<<endl;
cout<<"hey"<<endl;
}
fin.close();
}
I am making a binary tree. There are pointers to left and right child in my tree and a key and a string value for each node. In my destructor I am reading from a file and storing the key and value in a node. Every line of the file has the following format:
"M. Ubiquity~ 14100148"
- the Value is the name followed by the key.
Whenever I run this code, I get segmentation fault error but I can't seem to find the fault.
Any hint/help will be appreciated.

Answer 1

You have Root=NULL; and then few lines later TreeNode<T> *temp = Root; so you have temp=NULL.
Obviously the while (temp!=NULL) never executes and after while loop you have temp->value=buffer; which cause segementation fault!

Answer 2

Pointers can only associated with memory addresses, not values. Mainly there are two ways: If you have an automatic variable, you can assign its address to a pointer like this:
int i = 6; //automatic variable
int *pi = &i;
std::cout << pi; // you get the address of pi (hexadecimal number)
std::cout << *pi; // 6
Or you can allocate memory manually. The main thing is if you allocated memory to a variable, you also have to deallocate it or your program will have "memory leak".
int *pi = new int(6);
delete pi;
So if you place new elements in the tree, you have to allocate memory for them, and if you delete an element, you have to destruct with delete. You have to care about not to broke the list.