i am running linked linked destructor to delete linked list but i'm getting segmentation fault-CodePudding

this code is giving me segmentation fault as i am trying to delete linked list using destructor

~Node()
    {
        
    Node *current = this ;
    Node *previous = NULL;

    while(current != NULL)
    {
        previous = current;
        current = current->next;
        delete previous;
        previous = NULL;
        

    }

CodePudding user response：

You may not delete the current node itself because otherwise the code invokes undefined behavior.

Instead you could write

~Node()
{
    delete next;
}

And if the list is defined as a pointer to the head node then you need to write

delete head;

Here is a demonstration program

#include <iostream>

class Node
{
private:
    int data;
    Node *next;

public:

    explicit Node( int data, Node *next = nullptr ) : data( data ), next( next )
    {
    }

    ~Node()
    {
        std::cout << "Deleting " << data << "...\n";
        delete next;
    }
};

void push_front( Node *&head, int data )
{
    head = new Node( data, head );
}

int main()
{
    Node *head = nullptr;
    const int N = 10;

    for (int i = 0; i < N; i  )
    {
        push_front( head, N - i );
    }

    delete head;
}

The program output is

Deleting 1...
Deleting 2...
Deleting 3...
Deleting 4...
Deleting 5...
Deleting 6...
Deleting 7...
Deleting 8...
Deleting 9...
Deleting 10...

CodePudding user response：

You should exclude the current node from the delete operator, as the code is already a response to such a delete. Doing it again is like running in circles.

So modify your code to this:

~Node()
{
    Node *current = this->next; // exclude current node
    Node *previous;

    while (current != NULL)
    {
        previous = current;
        current = current->next;
        delete previous;
    }
}

There is no need to set previous to NULL, since it will run out of scope.

This code assumes that this is the first node of the list, which would be the natural thing to execute delete on. If for some reason you would execute delete on a node somewhere in the middle of a list, with the aim to discard the whole list, then you would need to repeat the above loop also for the nodes that precede the current node.