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Pointer to Pointer in C language

Introduction

Definition : It is possible to make a pointer to point to another pointer variable. A variable which contains address of a pointer variable is called pointer to a pointer. For example, consider the following declarations:

int a;
int *p1;
int *p2;

  • The first declaration instructs the compiler to allocate the memory for the variable a in which integer data can be stored.
  • The second declaration tells the compiler to allocate a memory for the variable p1 in which address of an integer variable can be stored.
  • The third declaration tells the compiler to allocate a memory for the variable p2 in which address of a pointer variable which points to an integer can be stored. The memory organization for the above three declaration is shown below:
Pointer to Pointer in C programming



Example: Memory organization after executing following assignment statement:
a=10;
p1=&a;
p2=&p1;

The memory organization after executing the statement a=10 is shown below:


The memory organization after executing the statement a=10


The memory organization after executing the statement p1=&a is shown below:

The memory organization after executing the statement p1=&a

The memory organization after executing the statement p2=&p1 is shown below:


The memory organization after executing the statement p2=&p1

The data item 10 can be accessed using three variables a, p1 and p2 as shown below:
a    refers to the data item 10
*p1 Also refers to the data item 10. Here, using p1 and only one indirection operator, the data item 10 can be accessed.
**p2  Also refers to the data item 10. Here, using p2 and two indirection operators the data item 10 can be accessed (i.e., *p2 refers to p1 and **p2 refers to a)


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Memory representation of Linked List Data Structures in C Language

Memory representation of Linked List

             In memory the linked list is stored in scattered cells (locations).The memory for each node is allocated dynamically means as and when required. So the Linked List can increase as per the user wish and the size is not fixed, it can vary.

               Suppose first node of linked list is allocated with an address 1008. Its graphical representation looks like the figure shown below:


      Suppose next node is allocated at an address 506, so the list becomes,



  Suppose next node is allocated with an address with an address 10,s the list become,


The other way to represent the linked list is as shown below:




 In the above representation the data stored in the linked list is “INDIA”, the information part of each node contains one character. The external pointer root points to first node’s address 1005. The link part of the node containing information I contains 1007, the address of next node. The last node …