How do I get rid of my segmentation fault

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1.00/5 (1 vote)

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#include "binTree.h"
#include <algorithm>
#include <iostream>
#include <iomanip>

using namespace std;

#ifndef BINSTREE_H
#define BINSTREE_H

template <class T>
class binSTree : public binTree <t>
{
public:
binSTree( Node <t> *r = NULL ): binTree<t>::binTree(r) {}
void insert(const T& x){ insert(root, x); }
void remove(const T& x){ remove(root, x); }
unsigned size() const{ return size(root); }
protected:
Node <t> * root;
private:
void insert(Node <t>*&, const T& );
void remove(Node <t> *&, const T&);
unsigned size( Node<t>* node) const{
int l;
int ll;
int lr;
if(!node){ l = 0; }
else if(!node->left && !node->right){ l = 1; }
else{
ll = size(node->left);
lr = size(node->right);
l=ll+lr;
}
return l; }
Node <t>* pred( Node<t>*& node){
node = node->left;
while(node != NULL){ node = node->right; }
return node;}

};

template <class T>
void binSTree<t>::insert(Node <t>*& node, const T& x)
{
if(!node){ node = new Node<t>(x); }
else if( x < node->data ){ insert(node->left, x); }
else if( x > node->data ){ insert(node->right, x); }
}

template <class T>
void binSTree<t>::remove(Node <t> *& node, const T& x)
{
if(x < node->data){ remove(node->left, x); }
else if(x > node->data){ remove(node->right, x); }
else if(x == node->data)
{
if(node->left == NULL && node->right == NULL){ delete node; }
else if( node->left != NULL )
{
Node<t>* temp = pred(node);
temp->left = node->left;
delete node;
}
else if(node->right != NULL )
{
Node<t>* temp = pred(node);
temp->right = node->right;
delete node;
}
else
{
Node<t>* temp = pred(node);
node = node->left;
while(node->right != NULL){ node = node->right; }
node = temp;
Node<t>* temp2 = pred(node);
delete temp;
temp2->left = node;
}
}
}
#endif

What I have tried:

I'm sure the problem is here somewhere, I've mostly been eliminating loops trying to find the problem

not sure where to start

it's a seg fault core dump

Posted 2-Nov-17 14:47pm

Member 13500537

Updated 2-Nov-17 22:40pm

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Peter_in_2780 2-Nov-17 21:04pm

One word. DEBUGGER

Member 13500537 2-Nov-17 22:00pm

Debugger just told me it's crashing at if(x < node->data) and that statement should be right?

in the insert function first iteration

nv3 3-Nov-17 2:16am

Well, if the debugger blames the statement "if (x < node->data)" then look at the value of node. My guess is that it is 0 or undefined, which in produces the segmentation fault. The next step is to find out, why node has the wrong value in that particular test situation. That's how debugging works.

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Patrice T · Answer 1 · 2017-11-02T17:00:00

Quote:
How do I get rid of my segmentation fault

Your code is not autonomous, we can't reproduce the problem, just guess.
Use the debugger to inspect variables, and check that any empty pointer is NULL as expected.
-----
Learn to indent properly your code, it show its structure and it helps reading and understanding.

C++

#include "binTree.h"
#include <algorithm>
#include <iostream>
#include <iomanip>

using namespace std;

#ifndef BINSTREE_H
#define BINSTREE_H

template <class T>
class binSTree : public binTree <t>
  {
    public:
      binSTree( Node <t> *r = NULL ): binTree<t>::binTree(r) {}
      void insert(const T& x){ insert(root, x); }
      void remove(const T& x){ remove(root, x); }
      unsigned size() const{ return size(root); }
    protected:
      Node <t> * root;
    private:
      void insert(Node <t>*&, const T& );
      void remove(Node <t> *&, const T&);
      unsigned size( Node<t>* node) const{
        int l;
        int ll;
        int lr;
        if(!node)
        {
          l = 0;
        }
        else if(!node->left && !node->right)
        {
          l = 1;
        }
        else{
          ll = size(node->left);
          lr = size(node->right);
          l=ll+lr;
        }
        return l;
      }
      Node <t>* pred( Node<t>*& node){
        node = node->left;
        while(node != NULL)
        {
          node = node->right;
        }
      return node;}

    };

    template <class T>
    void binSTree<t>::insert(Node <t>*& node, const T& x)
      {
        if(!node)
        {
          node = new Node<t>(x);
        }
        else if( x < node->data )
        {
          insert(node->left, x);
        }
        else if( x > node->data )
        {
          insert(node->right, x);
        }
      }

    template <class T>
    void binSTree<t>::remove(Node <t> *& node, const T& x)
      {
        if(x < node->data)
        {
          remove(node->left, x);
        }
        else if(x > node->data)
        {
          remove(node->right, x);
        }
        else if(x == node->data)
        {
          if(node->left == NULL && node->right == NULL)
          {
            delete node;
          }
          else if( node->left != NULL )
          {
            Node<t>* temp = pred(node);
            temp->left = node->left;
            delete node;
          }
          else if(node->right != NULL )
          {
            Node<t>* temp = pred(node);
            temp->right = node->right;
            delete node;
          }
          else
          {
            Node<t>* temp = pred(node);
            node = node->left;
            while(node->right != NULL)
            {
              node = node->right;
            }
            node = temp;
            Node<t>* temp2 = pred(node);
            delete temp;
            temp2->left = node;
          }
        }
      }
      #endif

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CPallini · Answer 2 · 2017-11-02T21:44:00

Quote:
Debugger just told me it's crashing at if(x < node->data) and that statement should be right?

because you didn't perform a sanity check:

C++

if ( ! node )
{
  // handle error
}

or

C++

assert(node);

Anyway, as others suggested, then you have to use the debugger to discover why the buggy condition occurred.

Jochen Arndt · Answer 3 · 2017-11-02T22:40:00

Your root member is not initialised.
I guess it should be set to the value passed in the constructor:

C++

binSTree( Node <t> *r = NULL ): binTree<t>::binTree(r), root(r) {}

You must also set the passed Node pointer to NULL after deleting it in the remove() function:

// ...
Node<t>* temp = pred(node);
temp->left = node->left;
delete node;
// Insert this line after each delete
node = NULL;
// ...

Your pred() function returns always NULL:

Node <t>* pred( Node<t>*& node)
{
    // Missing check for NULL here
    node = node->left;
    while(node != NULL)
        node = node->right; 
    // node is always NULL here!
    return node;
}

The function is also changing the content because node is passed by reference. It would be better to pass a const pointer instead and make the function const too.

Finally you should - as already suggested - always check if passed Node pointers are NULL. But these checks will fail (indicate success) for non-null but invalid pointers (not initialised or deleted meanwhile).

How do I get rid of my segmentation fault

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