Self Referential structures are those structures that have one or more pointers which point to the same type of structure, as their member.
In other words, structures pointing to the same type of structures are self-referential in nature
Example:
CPP
struct node { int data1; char data2; struct node* link;};int main(){ struct node ob; return 0;} |
Python3
class node: def __init__(self): self.data1=0 self.data2='' self.link=Noneif __name__ == '__main__': ob=node() |
Javascript
// Define the 'node' objectclass node { constructor(data1, data2) { this.data1 = data1; this.data2 = data2; this.link = null; }}// Create an instance of the 'Node' objectlet ob = new Node(); |
In the above example ‘link’ is a pointer to a structure of type ‘node’. Hence, the structure ‘node’ is a self-referential structure with ‘link’ as the referencing pointer.
An important point to consider is that the pointer should be initialized properly before accessing, as by default it contains garbage value.
Types of Self Referential Structures
- Self Referential Structure with Single Link
- Self Referential Structure with Multiple Links
Self Referential Structure with Single Link: These structures can have only one self-pointer as their member. The following example will show us how to connect the objects of a self-referential structure with the single link and access the corresponding data members. The connection formed is shown in the following figure.
Implementation:
C++
#include <stdio.h>struct node { int data1; char data2; struct node* link;};int main(){ struct node ob1; // Node1 // Initialization ob1.link = NULL; ob1.data1 = 10; ob1.data2 = 20; struct node ob2; // Node2 // Initialization ob2.link = NULL; ob2.data1 = 30; ob2.data2 = 40; // Linking ob1 and ob2 ob1.link = &ob2; // Accessing data members of ob2 using ob1 printf("%d", ob1.link->data1); printf("\n%d", ob1.link->data2); return 0;} |
Java
// java implementation of above approachpublic class Main { static class Node { int data1; int data2; Node link; } public static void main(String[] args) { Node ob1 = new Node(); // Node1 // Initialization ob1.link = null; ob1.data1 = 10; ob1.data2 = 20; Node ob2 = new Node(); // Node2 // Initialization ob2.link = null; ob2.data1 = 30; ob2.data2 = 40; // Linking ob1 and ob2 ob1.link = ob2; // Accessing data members of ob2 using ob1 System.out.println(ob1.link.data1); System.out.println(ob1.link.data2); }}// This code is implemented by Chetan Bargal |
Python3
class node: def __init__(self): self.data1=0 self.data2=0 self.link=Noneif __name__ == '__main__': ob1=node() # Node1 # Initialization ob1.link = None ob1.data1 = 10 ob1.data2 = 20 ob2=node() # Node2 # Initialization ob2.link = None ob2.data1 = 30 ob2.data2 = 40 # Linking ob1 and ob2 ob1.link = ob2 # Accessing data members of ob2 using ob1 print(ob1.link.data1) print(ob1.link.data2) |
C#
using System;public class MainClass { public class Node { public int data1; public int data2; public Node link; } public static void Main(string[] args) { Node ob1 = new Node(); // Node1 // Initialization ob1.link = null; ob1.data1 = 10; ob1.data2 = 20; Node ob2 = new Node(); // Node2 // Initialization ob2.link = null; ob2.data1 = 30; ob2.data2 = 40; // Linking ob1 and ob2 ob1.link = ob2; // Accessing data members of ob2 using ob1 Console.WriteLine(ob1.link.data1); Console.WriteLine(ob1.link.data2); }} |
Javascript
class node { constructor() { this.data1 = 0; this.data2 = 0; this.link = null; }}// Create node1let ob1 = new node();// Initializationob1.link = null;ob1.data1 = 10;ob1.data2 = 20;// Create node2let ob2 = new node();// Initializationob2.link = null;ob2.data1 = 30;ob2.data2 = 40;// Linking ob1 and ob2ob1.link = ob2;// Accessing data members of ob2 using ob1console.log(ob1.link.data1);console.log(ob1.link.data2); |
30 40
Self Referential Structure with Multiple Links: Self referential structures with multiple links can have more than one self-pointers. Many complicated data structures can be easily constructed using these structures. Such structures can easily connect to more than one nodes at a time. The following example shows one such structure with more than one links.
The connections made in the above example can be understood using the following figure.
Implementation:
CPP
#include <stdio.h>struct node { int data; struct node* prev_link; struct node* next_link;};int main(){ struct node ob1; // Node1 // Initialization ob1.prev_link = NULL; ob1.next_link = NULL; ob1.data = 10; struct node ob2; // Node2 // Initialization ob2.prev_link = NULL; ob2.next_link = NULL; ob2.data = 20; struct node ob3; // Node3 // Initialization ob3.prev_link = NULL; ob3.next_link = NULL; ob3.data = 30; // Forward links ob1.next_link = &ob2; ob2.next_link = &ob3; // Backward links ob2.prev_link = &ob1; ob3.prev_link = &ob2; // Accessing data of ob1, ob2 and ob3 by ob1 printf("%d\t", ob1.data); printf("%d\t", ob1.next_link->data); printf("%d\n", ob1.next_link->next_link->data); // Accessing data of ob1, ob2 and ob3 by ob2 printf("%d\t", ob2.prev_link->data); printf("%d\t", ob2.data); printf("%d\n", ob2.next_link->data); // Accessing data of ob1, ob2 and ob3 by ob3 printf("%d\t", ob3.prev_link->prev_link->data); printf("%d\t", ob3.prev_link->data); printf("%d", ob3.data); return 0;} |
Python3
class node: def __init__(self): self.data=0 self.prev_link=None self.next_link=Noneif __name__ == '__main__': ob1=node() #Node1 # Initialization ob1.prev_link = None ob1.next_link = None ob1.data = 10 ob2=node() #Node2 # Initialization ob2.prev_link = None ob2.next_link = None ob2.data = 20 ob3=node() # Node3 # Initialization ob3.prev_link = None ob3.next_link = None ob3.data = 30 # Forward links ob1.next_link = ob2 ob2.next_link = ob3 # Backward links ob2.prev_link = ob1 ob3.prev_link = ob2 # Accessing data of ob1, ob2 and ob3 by ob1 print(ob1.data,end='\t') print(ob1.next_link.data,end='\t') print(ob1.next_link.next_link.data) # Accessing data of ob1, ob2 and ob3 by ob2 print(ob2.prev_link.data,end='\t') print(ob2.data,end='\t') print(ob2.next_link.data) # Accessing data of ob1, ob2 and ob3 by ob3 print(ob3.prev_link.prev_link.data,end='\t') print(ob3.prev_link.data,end='\t') print(ob3.data) |
10 20 30 10 20 30 10 20 30
In the above example we can see that ‘ob1’, ‘ob2’ and ‘ob3’ are three objects of the self referential structure ‘node’. And they are connected using their links in such a way that any of them can easily access each other’s data. This is the beauty of the self referential structures. The connections can be manipulated according to the requirements of the programmer.
Applications: Self-referential structures are very useful in creation of other complex data structures like:
- Linked Lists
- Stacks
- Queues
- Trees
- Graphs etc.
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