Pointers

 

Pointers

Every variable is a memory location and every memory location has its address defined which can be accessed using ampersand (&) operator, which denotes an address in memory.

The pointers perform the function of storing the addresses of other variables in the program. These variables could be of any type- char, int, function, array, or other pointers.

an example where we define a pointer storing an integer’s address in a program.

int x = 10;

int* p = &x;

Here, the variable p is of pointer type, and it is pointing towards the address of the x variable, which is of the integer type.

Declaration of a Pointer

declare a pointer before using it to store any variable address. we can get the memory address of a variable with the reference operator &.

• The datatype indicates which type of variable is the pointer pointing to in the code.
• The asterisk (*) is used to declare a pointer.

type *var-name;

 Eg.

 int    *ip;    /* pointer to an integer */

double *dp;    /* pointer to a double */

float  *fp;    /* pointer to a float */

char   *ch     /* pointer to a character */

 Syntax of Pointer Initialization

pointer = &variable;

#include <stdio.h>

 int main () 

{

    int  var = 20;   /* actual variable declaration */

   int  *ip;        /* pointer variable declaration */

    ip = &var;  /* store address of var in pointer variable*/

    printf("Address of var variable: %x\n", &var  );

    /* address stored in pointer variable */

   printf("Address stored in ip variable: %x\n", ip );

    /* access the value using the pointer */

   printf("Value of *ip variable: %d\n", *ip );

    return 0;

}

 Dereferencing pointers

In the example above, we used the pointer variable to get the memory address of a variable (used together with the & reference operator).

to get the value of the variable the pointer points to, by using the * operator (the dereference operator):

Example

int myAge = 24;     // Variable declaration
int* ptr = &myAge;  // Pointer declaration

// Reference: Output the memory address of myAge with the pointer (0x7ffe5367e044)
printf("%p\n", ptr);

// Dereference: Output the value of myAge with the pointer (24)
printf("%d\n", *ptr);

                     Pointer arithmetic

 A pointer in c is an address, which is a numeric value. Therefore, you can perform arithmetic operations on a pointer just as you can on a numeric value.

There are four arithmetic operators that can be used on pointers:

Incrementing (++)

Decrementing (- -)

Addition (+)

Subtraction (-)

                              Pointer to Pointer

 A pointer to a pointer is a form of multiple indirections, or a chain of pointers. Normally, a pointer contains the address of a variable. When we define a pointer to a pointer, the first pointer contains the address of the second pointer, which points to the location that contains the actual value 

Syntax: int **ptr;

Eg.

int var = 10;   

// Let's say the address of this variable is 0xdbfeb8

int *ptr = &var;

// Value in ptr is 0xdbfeb8 and say the address of ptr is 0xdbfeb0

int **double_ptr = &ptr;

// The value stored in double_ptr is 0xdbfeb0

 Array and Pointers

int arr [20];

int *q [20] = &arr; // The q variable of the pointer type is pointing towards the integer array’s address or the address of arr.

The memory address of the first element is the same as the name of the array:

An array is a block of sequential data. Let's write a program to print addresses of array elements.

Eg.

#include <stdio.h>

int main() 

{

   int i, x[6], sum = 0;

   printf("Enter 6 numbers: ");

   for(i = 0; i < 6; ++i) {

  // Equivalent to scanf("%d", &x[i]);

      scanf("%d", x+i);

   // Equivalent to sum += x[i]

      sum += *(x+i);

  }

   printf("Sum = %d", sum);

   return 0;

}

we have declared an array x of 6 elements. To access elements of the array, we have used pointers.

Function and pointers

void display (int);

void(*q) (int) = &show; // The q pointer is pointing towards the function’s address in the program

In Functions Pointers, function’s name can be used to get function’s address.

A function can also be passed as an argument and can be returned from a function.

Declaration

function_return_type(*Pointer_name) (function argument list)

eg.

 #include<stdio.h>

int subtraction (int a, int b)

 {

   return a-b;

}

int main ()

{

   int (*fp) (int,int) =subtraction;

   //Calling function using function pointer

   int result = fp(5, 4);

  printf(" Using function pointer we get the result: %d",result);

   return 0;

}

 

 

 

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Milan Tomic

Hi. I’m Designer of Blog Magic. I’m CEO/Founder of ThemeXpose. I’m Creative Art Director, Web Designer, UI/UX Designer, Interaction Designer, Industrial Designer, Web Developer, Business Enthusiast, StartUp Enthusiast, Speaker, Writer and Photographer. Inspired to make things looks better.

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