Wild and Double Pointer :

Wild Pointers:
If a pointer is not initialised to anything, not even NULL, is called a Wild Pointer. The pointer is assigned to a garbage value which may not even be a valid address. Such pointers point to some arbitrary memory location.
Let us look at the code snippet below to understand wild pointers:

    int  main() {
       int  * ptr;  // ptr is a wild pointer
       int  num = 10;
       p = & x; //ptr is not a wild pointer anymore
       return  0;
    }

 

  • ptr is an int type pointer. Since it has not been initialized to anything, not even NULL, it is a wild pointer.
  • When ptr is made to point to num, it stores the address of num. Since now ptr is pointing to a valid memory address, it is not a wild pointer anymore.

Double Pointers:
A pointer to a pointer is called a double pointer.
Lets say we have two pointers and a normal variable.
The first pointer stores the address of a variable. The second pointer, which is the double pointer, stores the address of the first pointer. A double pointer is also known as pointer-to-pointer.
Declaring a double pointer is similar to declaring a pointer.
Syntax:

type **pointerName
  • typespecifies the type of the pointer. It must a valid type in C.
  • ** indicate that the pointer is a double pointer.
  • pointerNameis the name of the pointer variable.

Let us look at a code snippet to understand double pointers:

#include<stdio.h>
     
    int main()
    {
        int num = 10; //normal variable
         
         
        int *ptr1; // pointer for num
         
        int **ptr2; // double pointer for ptr1
         
        ptr1 = # // assigning address of num in ptr1
                
               ptr2 = &ptr1; // assigning address of ptr1 in ptr2
         
        printf("Value of num = %d\n", num );
        printf("Value of num using single pointer = %d\n", *ptr1 );
        printf("Value of num using double pointer = %d\n", **ptr2);
    }

 

  • We have created an int type variable numthat stores value 10
  • We have created a pointer ptr1to point to num
  • We have created a pointer ptr2 to point to ptr1
  • ptr1 stores the address of numand ptr2 stores the address of ptr1

The above code snippet gives the following output:

Value of num = 10
Value of num using single pointer = 10
Value of num using double pointer = 10

The diagram is a pictorial representation of the above code.

Some important statements to remember concerning single and double pointers:

Statement Output
*ptr1 10
**ptr2 10
ptr1 &num (i.e. address of num)
ptr2 &ptr1 (i.e. address of ptr)

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CopyRight © 2019