value lost after assignment in a pointer - c++

Question

This code is printing 0 for this->min_node->right and this->min_node->left in the function add_node_to_the_list. I am not able to figure out why it is happening when I have assigned some values to this variables in previous iterations. This value is available when I am printing it in the main but after calling the function this value is lost.
#include<iostream>
#include<vector>
#include<iterator>
namespace a1{
/******************************Declarations*********************************/
class node{
//Private member declaration
//Public member declaration
public: int key;
public: int degree;
public: bool mark;
public: node * left;
public: node * right;
public: node * child;
public: node * parent;
//Private method declaration
//Public method declaration
public: node(int);
};
class heap{
//Private member declaration
private: int node_count;
private: void add_node_to_the_list(node *);
//Public member declaration
public: node * min_node;
//Private method declaration
private: void consolidate();
private: void fib_heap_link(node *, node *);
private: void cut(node *, node *);
private: void cascading_cut(node *);
//Public method declaration
public: heap();
public: void fib_heap_insert(int);
public: void fib_heap_union(heap &);
public: heap & fib_heap_extract_min();
public: void fib_heap_decrease_key(node *, int);
public: void fib_heap_delete(node *);
public: int get_node_count();
};
};//End of namespace a1
/****************************Definitions*************************************/
/****************************node functions here*****************************/
a1::node::node(int key){
this->key = key;
this->degree = 0;
this->mark = false;
this->left = NULL;
this->right = NULL;
this->child = NULL;
this->parent = NULL;
}
/****************************Heap functions here*****************************/
//Private methods
void a1::heap::add_node_to_the_list(node * temp){
if(this->min_node == NULL){
this->min_node = temp;
this->min_node->right = this->min_node;
this->min_node->left = this->min_node;
}
else{
temp->right = this->min_node->right;
temp->left = this->min_node;
//this->min_node->right->left = temp;
//this->min_node->right = temp;
}
}
//Public methods
a1::heap::heap(){
this->node_count = 0;
this->min_node = NULL;
}
void a1::heap::fib_heap_insert(int key){
a1::node temp(key);
if(this->min_node == NULL){
a1::heap::add_node_to_the_list(&temp);
this->min_node = &temp;
}
else{
std::cout << "Printing this->min_node->right : " << this->min_node->right << std::endl;
std::cout << "Printing this->min_node->left : " << this->min_node->left << std::endl;
a1::heap::add_node_to_the_list(&temp);
if(this->min_node->key > temp.key){
this->min_node = &temp;
}
}
this->node_count += 1;
}
int a1::heap::get_node_count(){
return this->node_count;
}
/**************************Debug functions***********************************/
using namespace a1;
void print_fib_heap(node * n){
if(n == NULL) return;
else{
node * min_node;
node * trav;
bool flag = false;
min_node = n;
trav = n;
while(flag == false || trav != min_node){
flag = true;
std::cout << "(" << "key = " << trav->key << " d = " << trav->degree;
print_fib_heap(trav->child);
std::cout << ")";
trav = trav->right;
}
}
}
/**************************Main Function to test*****************************/
int main(){
heap h1;
h1.fib_heap_insert(2);
std::cout << "From main h1.min_node->right: " << h1.min_node->right << std::endl;
h1.fib_heap_insert(3);
//print_fib_heap(h1.min_node);
return 0;
}

Answer 1

this->min_node = &temp is saving the address of a local stack variable, which won't be valid as soon as the method returns. The results would then be undefined.
I would suggest using new for that object in a1::heap::fib_heap_insert().