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C - Delete the first node of the Doubly Linked List



In this method, the first node of the doubly linked list is deleted. For example - if the given list is 10->20->30->40 and the first node is deleted, the list becomes 20->30->40.

Deleting the first node of the Doubly Linked List is very easy. If the head is not null then create a temp node pointing to head and move head to the next of head. Then delete the temp node. If the new head is not null, make the prev of it as null.

Doubly Linked List - Delete First Node

The function pop_front is created for this purpose. It is a 4-step process.

void pop_front(struct Node** head_ref) {
  if(*head_ref != NULL) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    struct Node *temp = *head_ref;
     
    //2. move head to next of head
    *head_ref = (*head_ref)->next;

    //3. delete temp node
    temp = NULL;  

    //4. If the new head is not null, then
    //   make prev of the new head as null
    if(*head_ref != NULL) 
      (*head_ref)->prev = NULL;
  }    
}

The below is a complete program that uses above discussed concept of deleting the first node of the doubly linked list.

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

//node structure
struct Node {
  int data;
  struct Node* next;
  struct Node* prev;
};

//Add new element at the end of the list
void push_back(struct Node** head_ref, int newElement) {  
  struct Node *newNode, *temp;
  newNode = (struct Node*)malloc(sizeof(struct Node)); 
  newNode->data = newElement;  
  newNode->next = NULL;
  newNode->prev = NULL;
  if(*head_ref == NULL) {
    *head_ref = newNode;
  } else {
    temp = *head_ref;
    while(temp->next != NULL) {
      temp = temp->next;
    }    
    temp->next = newNode;
    newNode->prev = temp;
  }
}

//Delete first node of the list
void pop_front(struct Node** head_ref) {
  if(*head_ref != NULL) {
    struct Node *temp = *head_ref;
    *head_ref = (*head_ref)->next;
    temp = NULL; 
    if(*head_ref != NULL) 
      (*head_ref)->prev = NULL;
  }    
}

//display the content of the list
void PrintList(struct Node* head_ref) {
  struct Node* temp = head_ref;
  if(head_ref != NULL) {
    printf("The list contains: ");
    while (temp != NULL) {
      printf("%i ",temp->data);
      temp = temp->next;  
    }
    printf("\n");
  } else {
    printf("The list is empty.\n");
  }   
}

// test the code 
int main() {
  struct Node* MyList = NULL;

  //Add four elements in the list.
  push_back(&MyList, 10);
  push_back(&MyList, 20);
  push_back(&MyList, 30);
  push_back(&MyList, 40);
  PrintList(MyList);

  //Delete the first node
  pop_front(&MyList);
  PrintList(MyList);

  return 0; 
}

The above code will give the following output:

The list contains: 10 20 30 40
The list contains: 20 30 40 

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