Tree Implementation giving segmentation fault(core dump) error c++ 11

Question

Recently, I coded linked list with C++11. Using those concepts, I tried to code tree{a very basic tree} implementation in C++11. But it is giving me a Segmentation fault. I checked online and found out that it happens when the program tries to write a read access memory or tries to access free memory, but I can't figure out how it's happening here. Please help..

#include<iostream>
#include<cstdlib>
using namespace std;
struct node{
    node *left;
    node *right;
    int key;
};
class tree{
    public:
    node *root;
    tree(){
        root->left=NULL;
        root->right=NULL;
    }
    node *createnode(int data){
        node *temp=new node;
        temp->key=data;
        temp->left=NULL;
        temp->right=NULL;
        return temp;
    }
};
int main(){
    tree t;
    node *root;
    root=t.createnode(1);
    //root->left=t.createnode(2);
    //root->right=t.createnode(3);
    //root->left->left=t.createnode(9);
    //root->left->right=t.createnode(7);
return 0;
}

check image

In tree() you access variable root, but you didn't initialize it. — zdenek
– zdenek, Commented Apr 25, 2018 at 17:30

Miles Budnek · Accepted Answer · 2018-04-25 17:30:27Z

5

t.root is uninitialized, so writing to root->left and root->right in tree's constructor invokes undefined behavior.

Right now, your tree class doesn't really make much sense. It contains a root node pointer, but you never use it. createnode could just be a free function or a static member of node. Better would be to encapsulate nodes entirely and just have tree have an insert method that takes an int, creates a new node, and inserts it at the appropriate place in the tree.

answered Apr 25, 2018 at 17:30

Miles Budnek

31.4k2 gold badges44 silver badges65 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

JimmyFails Over a year ago

Thanks, i initailised it and it worked. But I didn't get your last sentence. What do you mean by encapsulating node entirely? Can you give me an example..

Miles Budnek Over a year ago

@JimmyFails I mean make node private to tree so users of the tree class don't need to know about it or interact with it at all. Make it an implementation detail rather than part of tree's interface. For example, std::map has a node class that it uses internally, but to use std::map you don't have to know or think about nodes.

Jesper Juhl · Accepted Answer · 2018-04-25 17:35:23Z

0

Your problem is in the constructor:

class tree{
    public:
    node *root;
    tree(){
        root->left=NULL;
        root->right=NULL;
    }

You declare root in the class, but you never initialize it. So when you dereference it in the body of the constructor, you are dereferencing a garbage pointer that could point to anything. Strictly speaking, what you are doing there is Undefined Behaviour and the compiler is well within its right to generate whatever it likes or even nothing at all for that bit of code.

Unrelated nitpick: don't use NULL in new code, use nullptr.

answered Apr 25, 2018 at 17:35

Jesper Juhl

32.2k4 gold badges55 silver badges80 bronze badges

Collectives™ on Stack Overflow

Tree Implementation giving segmentation fault(core dump) error c++ 11

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related