Self Referential Structures
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:
struct node {
int data1;
char data2;
struct node* link;
};
int main()
{
struct node ob;
return 0;
}
// Define the 'Node' class
class Node {
// Data members to store the data
int data1;
int data2;
// Reference to the next node
Node link;
// Constructor to initialize the data members
public Node(int data1, int data2)
{
this.data1 = data1;
this.data2 = data2;
this.link = null;
}
// Default constructor
public Node()
{
this.data1 = 0;
this.data2 = 0;
this.link = null;
}
}
// Main class to demonstrate the creation of Node instance
public class Main {
public static void main(String[] args)
{
// Create an instance of the 'Node' class using the
// default constructor
Node ob = new Node();
// Optionally, you can print the node's data to
// verify
System.out.println("Data1: " + ob.data1
+ ", Data2: " + ob.data2);
}
}
class node:
def __init__(self):
self.data1 = 0
self.data2 = ''
self.link = None
if __name__ == '__main__':
ob = node()
// Define the 'node' object
class node {
constructor(data1, data2) {
this.data1 = data1;
this.data2 = data2;
this.link = null;
}
}
// Create an instance of the 'Node' object
let ob = new Node();
Output
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:
#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 implementation of above approach
public 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
class node:
def __init__(self):
self.data1=0
self.data2=0
self.link=None
if __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)
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);
}
}
class node {
constructor() {
this.data1 = 0;
this.data2 = 0;
this.link = null;
}
}
// Create node1
let ob1 = new node();
// Initialization
ob1.link = null;
ob1.data1 = 10;
ob1.data2 = 20;
// Create node2
let ob2 = new node();
// 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.log(ob1.link.data1);
console.log(ob1.link.data2);
Output
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:
#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;
}
public class Main {
public static void main(String[] args)
{
// Create nodes
Node ob1 = new Node(); // Node1
Node ob2 = new Node(); // Node2
Node ob3 = new Node(); // Node3
// Initialize data for each node
ob1.data = 10;
ob2.data = 20;
ob3.data = 30;
// Set forward links
ob1.next_link = ob2;
ob2.next_link = ob3;
// Set backward links
ob2.prev_link = ob1;
ob3.prev_link = ob2;
// Accessing data of ob1, ob2 and ob3 by ob1
System.out.println(ob1.data + "\t"
+ ob1.next_link.data + "\t"
+ ob1.next_link.next_link.data);
// Accessing data of ob1, ob2 and ob3 by ob2
System.out.println(ob2.prev_link.data + "\t"
+ ob2.data + "\t"
+ ob2.next_link.data);
// Accessing data of ob1, ob2 and ob3 by ob3
System.out.println(ob3.prev_link.prev_link.data
+ "\t" + ob3.prev_link.data
+ "\t" + ob3.data);
}
}
class Node {
int data;
Node prev_link;
Node next_link;
}
class node:
def __init__(self):
self.data = 0
self.prev_link = None
self.next_link = None
if __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)
class Node {
constructor(data) {
this.data = data;
this.prev_link = null;
this.next_link = null;
}
}
function main() {
// Create nodes
let ob1 = new Node(); // Node1
let ob2 = new Node(); // Node2
let ob3 = new Node(); // Node3
// Initialize data for each node
ob1.data = 10;
ob2.data = 20;
ob3.data = 30;
// Set forward links
ob1.next_link = ob2;
ob2.next_link = ob3;
// Set backward links
ob2.prev_link = ob1;
ob3.prev_link = ob2;
// Accessing data of ob1, ob2, and ob3 by ob1
console.log(ob1.data + "\t" + ob1.next_link.data + "\t" + ob1.next_link.next_link.data);
// Accessing data of ob1, ob2, and ob3 by ob2
console.log(ob2.prev_link.data + "\t" + ob2.data + "\t" + ob2.next_link.data);
// Accessing data of ob1, ob2, and ob3 by ob3
console.log(ob3.prev_link.prev_link.data + "\t" + ob3.prev_link.data + "\t" + ob3.data);
}
// Execute the main function
main();
Output
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: