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in this function correct pointer not returned to the calling function

What are the differences between a pointer variable and a reference variable in C++?What is a smart pointer and when should I use one?Using global variables in a functionHow do function pointers in C work?Typedef function pointer?Why should I use a pointer rather than the object itself?Function says node is deleted but is not deletedPointers issue in linked list function's return I cannot figureLinked list delete node. Free(pointer) prints 0 in next nodeIn my Singly linked List implementation why is it even though I allocated memory for the node to be freed, the pointer to the Node isn't NULL?

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

2

the problem is when i print the list after deleting the node the printing function prints 0 in place of the deleted node.....but i wanted it to print nothing.

// the function call is delete_from_key(&head,i);
//node is struct linked_list
void delete_from_key(node *head, int key)

 node *new, *temp;
 if(head == NULL)
 
 printf("nothing to delete . the list is empty.n");
 return;
 
 else if(head->num == key)
 
 temp=head;
 head=temp->next;
 free(temp);
 return;
 
 new=search_key(head, key);//search_key returns pointer node holding the key.
 if(new != NULL)
 
 temp = new;
 new = new->next;
 free(temp);
 return;
 

example:

the list is 1-> 2-> 3-> 4-> 5->

if i called this function with key 2

the expected output is 1-> 3-> 4-> 5->

instead the actual output is 1-> 0-> 3-> 4-> 5->

c pointers scope dynamic-memory-allocation singly-linked-list

share|improve this question

edited Mar 26 at 6:43

acidus101

asked Mar 26 at 5:55

acidus101acidus101

1433 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Don'e spam tags. new is a keyword in C++, so there is no possible way this is part of a C++ program. Tags are to define the scope of a question correctly, not to gain exposure.
  
  – StoryTeller
  Mar 26 at 6:02
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  temp = new->next; //temp points to node holding the key...new->next = temp->next; //new->next points to node which is after the node holding the key....free(temp);
  
  – sameerkn
  Mar 26 at 6:08
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You have missed setting the previous pointer of new to next pointer of new when new is not NULL. You have to keep track of previous pointer of the node which you want to delete.
  
  – H.S.
  Mar 26 at 6:10
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @sameerkn don't answer in comments.
  
  – bolov
  Mar 26 at 6:11
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You have already checked if head is NULL in first if, so you don't need to check again in second...
  
  – Aconcagua
  Mar 26 at 6:15
  

  
  
  
  

 | 
show 1 more comment

2

the problem is when i print the list after deleting the node the printing function prints 0 in place of the deleted node.....but i wanted it to print nothing.

// the function call is delete_from_key(&head,i);
//node is struct linked_list
void delete_from_key(node *head, int key)

 node *new, *temp;
 if(head == NULL)
 
 printf("nothing to delete . the list is empty.n");
 return;
 
 else if(head->num == key)
 
 temp=head;
 head=temp->next;
 free(temp);
 return;
 
 new=search_key(head, key);//search_key returns pointer node holding the key.
 if(new != NULL)
 
 temp = new;
 new = new->next;
 free(temp);
 return;
 

example:

the list is 1-> 2-> 3-> 4-> 5->

if i called this function with key 2

the expected output is 1-> 3-> 4-> 5->

instead the actual output is 1-> 0-> 3-> 4-> 5->

c pointers scope dynamic-memory-allocation singly-linked-list

share|improve this question

edited Mar 26 at 6:43

acidus101

asked Mar 26 at 5:55

acidus101acidus101

1433 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Don'e spam tags. new is a keyword in C++, so there is no possible way this is part of a C++ program. Tags are to define the scope of a question correctly, not to gain exposure.
  
  – StoryTeller
  Mar 26 at 6:02
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  temp = new->next; //temp points to node holding the key...new->next = temp->next; //new->next points to node which is after the node holding the key....free(temp);
  
  – sameerkn
  Mar 26 at 6:08
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You have missed setting the previous pointer of new to next pointer of new when new is not NULL. You have to keep track of previous pointer of the node which you want to delete.
  
  – H.S.
  Mar 26 at 6:10
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @sameerkn don't answer in comments.
  
  – bolov
  Mar 26 at 6:11
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You have already checked if head is NULL in first if, so you don't need to check again in second...
  
  – Aconcagua
  Mar 26 at 6:15
  

  
  
  
  

 | 
show 1 more comment

the problem is when i print the list after deleting the node the printing function prints 0 in place of the deleted node.....but i wanted it to print nothing.

// the function call is delete_from_key(&head,i);
//node is struct linked_list
void delete_from_key(node *head, int key)

 node *new, *temp;
 if(head == NULL)
 
 printf("nothing to delete . the list is empty.n");
 return;
 
 else if(head->num == key)
 
 temp=head;
 head=temp->next;
 free(temp);
 return;
 
 new=search_key(head, key);//search_key returns pointer node holding the key.
 if(new != NULL)
 
 temp = new;
 new = new->next;
 free(temp);
 return;
 

example:

the list is 1-> 2-> 3-> 4-> 5->

if i called this function with key 2

the expected output is 1-> 3-> 4-> 5->

instead the actual output is 1-> 0-> 3-> 4-> 5->

c pointers scope dynamic-memory-allocation singly-linked-list

share|improve this question

edited Mar 26 at 6:43

acidus101

asked Mar 26 at 5:55

acidus101acidus101

1433 bronze badges

// the function call is delete_from_key(&head,i);
//node is struct linked_list
void delete_from_key(node *head, int key)

 node *new, *temp;
 if(head == NULL)
 
 printf("nothing to delete . the list is empty.n");
 return;
 
 else if(head->num == key)
 
 temp=head;
 head=temp->next;
 free(temp);
 return;
 
 new=search_key(head, key);//search_key returns pointer node holding the key.
 if(new != NULL)
 
 temp = new;
 new = new->next;
 free(temp);
 return;
 

share|improve this question

edited Mar 26 at 6:43

acidus101

asked Mar 26 at 5:55

acidus101acidus101

1433 bronze badges

share|improve this question

edited Mar 26 at 6:43

acidus101

asked Mar 26 at 5:55

acidus101acidus101

1433 bronze badges

asked Mar 26 at 5:55

acidus101acidus101

1433 bronze badges

asked Mar 26 at 5:55

acidus101acidus101

1433 bronze badges

2 Answers
2

active

oldest

votes

4

You need to update the previous node's next as well as it's next is getting deleted.

prev_node=search_key(head, key);//search_key returns pointer to the node just before the node holding the key.

if(prev_node!= NULL)

 // prev_node->next is the one that needs to be deleted
 temp = prev_node->next; 

 //Make the prev node point to the next node of the one that's getting deleted
 prev_node->next = temp->next; 

 free(temp);
 return;

share|improve this answer

edited Mar 26 at 6:17

answered Mar 26 at 6:10

Wander3rWander3r

75266 silver badges1818 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  i updated the search function but forgot to update the comment. i have edited it.thanks!
  
  – acidus101
  Mar 26 at 6:34
  

  
  
  
  

add a comment | 

3

First bug

head=temp->next;

Since head is a local parameter this assignment changes this local parameter. You need to change the pointer passed to the function, so you need your code to be:

void delete_from_key(node **head, int key)
 //...
 *head=temp->next;
 //...

2nd bug

new = new->next;

Kind of the same problem. new is a local variable. You are changing a local variable, you aren't changing the pointer within the list.

If search_key indeed returns pointer to the node before the found key you need

temp = new->next;
new->next = new->next->next;
free(temp);

share|improve this answer

answered Mar 26 at 6:10

bolovbolov

35.1k99 gold badges7979 silver badges145145 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  it worked thank you!
  
  – acidus101
  Mar 26 at 6:32
  

  
  
  
  

add a comment | 

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4

You need to update the previous node's next as well as it's next is getting deleted.

prev_node=search_key(head, key);//search_key returns pointer to the node just before the node holding the key.

if(prev_node!= NULL)

 // prev_node->next is the one that needs to be deleted
 temp = prev_node->next; 

 //Make the prev node point to the next node of the one that's getting deleted
 prev_node->next = temp->next; 

 free(temp);
 return;

share|improve this answer

edited Mar 26 at 6:17

answered Mar 26 at 6:10

Wander3rWander3r

75266 silver badges1818 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  i updated the search function but forgot to update the comment. i have edited it.thanks!
  
  – acidus101
  Mar 26 at 6:34
  

  
  
  
  

add a comment | 

4

You need to update the previous node's next as well as it's next is getting deleted.

prev_node=search_key(head, key);//search_key returns pointer to the node just before the node holding the key.

if(prev_node!= NULL)

 // prev_node->next is the one that needs to be deleted
 temp = prev_node->next; 

 //Make the prev node point to the next node of the one that's getting deleted
 prev_node->next = temp->next; 

 free(temp);
 return;

share|improve this answer

edited Mar 26 at 6:17

answered Mar 26 at 6:10

Wander3rWander3r

75266 silver badges1818 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  i updated the search function but forgot to update the comment. i have edited it.thanks!
  
  – acidus101
  Mar 26 at 6:34
  

  
  
  
  

add a comment | 

You need to update the previous node's next as well as it's next is getting deleted.

prev_node=search_key(head, key);//search_key returns pointer to the node just before the node holding the key.

if(prev_node!= NULL)

 // prev_node->next is the one that needs to be deleted
 temp = prev_node->next; 

 //Make the prev node point to the next node of the one that's getting deleted
 prev_node->next = temp->next; 

 free(temp);
 return;

share|improve this answer

edited Mar 26 at 6:17

answered Mar 26 at 6:10

Wander3rWander3r

75266 silver badges1818 bronze badges

prev_node=search_key(head, key);//search_key returns pointer to the node just before the node holding the key.

if(prev_node!= NULL)

 // prev_node->next is the one that needs to be deleted
 temp = prev_node->next; 

 //Make the prev node point to the next node of the one that's getting deleted
 prev_node->next = temp->next; 

 free(temp);
 return;

share|improve this answer

edited Mar 26 at 6:17

answered Mar 26 at 6:10

Wander3rWander3r

75266 silver badges1818 bronze badges

answered Mar 26 at 6:10

Wander3rWander3r

75266 silver badges1818 bronze badges

answered Mar 26 at 6:10

Wander3rWander3r

75266 silver badges1818 bronze badges

3

First bug

head=temp->next;

Since head is a local parameter this assignment changes this local parameter. You need to change the pointer passed to the function, so you need your code to be:

void delete_from_key(node **head, int key)
 //...
 *head=temp->next;
 //...

2nd bug

new = new->next;

Kind of the same problem. new is a local variable. You are changing a local variable, you aren't changing the pointer within the list.

If search_key indeed returns pointer to the node before the found key you need

temp = new->next;
new->next = new->next->next;
free(temp);

share|improve this answer

answered Mar 26 at 6:10

bolovbolov

35.1k99 gold badges7979 silver badges145145 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  it worked thank you!
  
  – acidus101
  Mar 26 at 6:32
  

  
  
  
  

add a comment | 

3

First bug

head=temp->next;

Since head is a local parameter this assignment changes this local parameter. You need to change the pointer passed to the function, so you need your code to be:

void delete_from_key(node **head, int key)
 //...
 *head=temp->next;
 //...

2nd bug

new = new->next;

Kind of the same problem. new is a local variable. You are changing a local variable, you aren't changing the pointer within the list.

If search_key indeed returns pointer to the node before the found key you need

temp = new->next;
new->next = new->next->next;
free(temp);

share|improve this answer

answered Mar 26 at 6:10

bolovbolov

35.1k99 gold badges7979 silver badges145145 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  it worked thank you!
  
  – acidus101
  Mar 26 at 6:32
  

  
  
  
  

add a comment | 

First bug

head=temp->next;

Since head is a local parameter this assignment changes this local parameter. You need to change the pointer passed to the function, so you need your code to be:

void delete_from_key(node **head, int key)
 //...
 *head=temp->next;
 //...

2nd bug

new = new->next;

Kind of the same problem. new is a local variable. You are changing a local variable, you aren't changing the pointer within the list.

If search_key indeed returns pointer to the node before the found key you need

temp = new->next;
new->next = new->next->next;
free(temp);

share|improve this answer

answered Mar 26 at 6:10

bolovbolov

35.1k99 gold badges7979 silver badges145145 bronze badges

head=temp->next;

void delete_from_key(node **head, int key)
 //...
 *head=temp->next;
 //...

new = new->next;

temp = new->next;
new->next = new->next->next;
free(temp);

share|improve this answer

answered Mar 26 at 6:10

bolovbolov

35.1k99 gold badges7979 silver badges145145 bronze badges

answered Mar 26 at 6:10

bolovbolov

35.1k99 gold badges7979 silver badges145145 bronze badges

answered Mar 26 at 6:10

bolovbolov

35.1k99 gold badges7979 silver badges145145 bronze badges