Self Referential Structures

03 Nov, 2021
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
Python3
struct node {    int data1;    char data2;    struct node* link;}; int main(){    struct node ob;    return 0;}
class node:    def __init__(self):        self.data1=0        self.data2=''        self.link=None if __name__ == '__main__':    ob=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 LinkSelf Referential Structure with Multiple Links
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.  
 
CPP
Python3
#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;}
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)
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.  
 
CPP
Python3
#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;}
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)
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
 
shubham_singh
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Data Structures
Data Structures
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