delete function

[Kittu20]

I am trying to delete current node in list

after deleting current list should print 4, 3, 2, 1

but program print strange value. How to delete current node

#include<stdio.h>#include<stdlib.h>


struct node
{
	int data;
	struct node *next;
};


void delete( struct node *current)
{
   if (current != NULL)
   {
	   free(current);
   } 	   
}
void instert( struct node **current, int value)
{
	struct node *new = malloc(sizeof(struct node));
	
	if ( new != NULL)
	{
		new-> data = value;
		new -> next = *current;
		*current = new;
	}
}


void List(struct node *current)
{
	while (current !=NULL)
	{
		printf("%d ", current -> data);
		current = current -> next;
	}
	
}


int main ()
{
	struct node *head = NULL;	
	
	instert(&head, 1); 
   	instert(&head, 2);
	instert(&head, 3);
	instert(&head, 4);
	instert(&head, 5);
	List(head);
	delete (head);
	printf("\n");
	List(head);
	return 0;
}

output

7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 7217968 7209152 7222088 ^C

[G4143]

Shouldn't delete have a way to access the new head?

[christop]

To delete a node from a list you need to modify the "next" pointer of the previous node in the list to point at the node following the node you're deleting.

As it is, all your delete function does is free the memory of a node. The node itself is still in the list, but since the memory has been freed, if you try to access the now-freed node (including just to print the list), you'll have a use-after-free bug.

[Kittu20]

To delete a node from a list you need to modify the "next" pointer of the previous node in the list to point at the node following the node you're deleting.

As it is, all your delete function does is free the memory of a node. The node itself is still in the list, but since the memory has been freed, if you try to access the now-freed node (including just to print the list), you'll have a use-after-free bug.

006A2310 // head node
006A15C8 // node 2
006A1598 // node 3
00000000 // last node

so pointer should be set to 006A15C8 to delete head node in list

#include<stdio.h>#include<stdlib.h>
 
 
struct node
{
    int data;
    struct node *next;
};
 
 
void delete( struct node *current)
{
   while (current != NULL)
   {
       current = current-> next;
	   printf(" %p \n", (void*)current-> next );
   }       
}
void instert( struct node **current, int value)
{
    struct node *new = malloc(sizeof(struct node));
     
    if ( new != NULL)
    {
        new-> data = value;
        new -> next = *current;
        *current = new;
    }
}
 
 
void List(struct node *current)
{
    while (current !=NULL)
    {
        printf("%d ", current -> data);
        current = current -> next;
    }
     
}
 
 
int main ()
{
    struct node *head = NULL;   
     
    instert(&head, 1); 
    instert(&head, 2);
    instert(&head, 3);
    instert(&head, 4);
    instert(&head, 5);
    delete (head);
    printf("\n");
    return 0;
}

[flp1969]

I suggest to draw, on paper, what you are trying to do...

[Kittu20]

I suggest to draw, on paper, what you are trying to do...

Done to delete current node

[Salem]

> void instert( struct node **current, int value)
The reason you have a node** is because you need to be able to modify the head pointer in some situations.

> void delete( struct node *current)
Which is why this also needs to be a node**, because you need to be able to modify the head pointer in some situations.

[Kittu20]

> void instert( struct node **current, int value)
The reason you have a node** is because you need to be able to modify the head pointer in some situations.

> void delete( struct node *current)
Which is why this also needs to be a node**, because you need to be able to modify the head pointer in some situations.

I can search and delete node in list on the paper.

I have to do two steps in the delete function in which i am struggling

step 1 : search the node that need to delete
step 2 : delete node if found in list and set pointer to point correct node

void delete( struct node **current)
{
   while (current != NULL)
   {
   
   }       
}

[Salem]

> I have to do two steps in the delete function in which i am struggling
Look at how you use current in your insert function.

[Kittu20]

> I have to do two steps in the delete function in which i am struggling
Look at how you use current in your insert function.

 void delete( struct node **current){
	struct node *temp = *current;  // Node 1
	
   while (temp != NULL)
   {
      temp = temp -> next;  // current node point to previous node in loop	  
   }       
}

I go from first node to last node in list but How to compare with the node i want to delete

[G4143]

This whole delete function can be solved and understood if you understand that C is a call by value language.
If you understand what call by value is and what a pointer variable is(hint - A pointer variable is just a variable that can hold a memory address)... Then you'll have this whole delete function mess sorted out.

[flp1969]

Done to delete current node

Ok... not what you thing you're doing, but what your code is currently doning, step by step...
THEN you'll see your mistake.

[Kittu20]

Ok... not what you thing you're doing, but what your code is currently doning, step by step...
THEN you'll see your mistake.

Is there any mistake in the diagram. I do not think so.

[G4143]

There isn't a mistake in your diagram. There is a shortcoming in your understanding of C's call by value mechanism.

Understand how C passes values to functions and you'll see what you have to do.

[flp1969]

Is there any mistake in the diagram. I do not think so.

OF COURSE there is a mistake.... Build the diagram step by step, following what the code is doing!!!