C Foundation

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Operators

What is Operator C Comma Operator C Arithmetic Operators C Relational Operators C Logical Operators C Bitwise Operators C Conditional Operators C : : Operator C Operator Priority

Basic IO's

Basic IO's C Formatted Functions C Unformatted Functions C Common Functions

Control Statements

What is Control Statement C if Statement C if else Statement C Nested if Statement C Else if Statement C Break Statement C Continue Statement C Switch Statement C Goto Statement

Looping

What is Control Loop C for Loop C Nested for Loop C while Loop C Nested while Loop C do while Loop C Nested do while loop

Functions

What is Function C User Defined Functions C Recursion C Passing Parameters

Scope

Scope C Local Scope C Global Scope

Storage Classes

What is Storage Class C Auto C Extern C Static C Register

Array

What is Array C One Dimensional Array C Two Dimensional Array C Multi Dimensional Array C Arrays Of Strings

String

What is String C String Functions

Pointer

What is Pointer C Pointers Arithmetic C Pointer to Pointer C Pointers and Arrays C Pointers and Strings C Pointer to Functions Void Pointers Null Pointers C Null and Void Pointer

Structure

What is Structure C Struct within Struct C Array within Structure C Pointer to Structure C Structure and Function C Enum C Bitfield Structure C Type def

Union

What is Union

Files

What is File C read a file C write a file C File Handling C Error Handling C Low Level Disk I/O C Other file functions

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What is Memory Allocation C Malloc() C Calloc() C Free() C Realloc() C Coreleft()

C Reference

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The ones who are crazy enough to think they can change the world are the ones who do.
- Steve Jobs

C Pointers

What Is Pointer

A Pointer is a variable that holds the address of another variable. In C, many complex tasks can be done only with pointers.

pointers in c

Syntax - Pointers

Syntax
data_type *variablename;

Declaring Pointer variable

  • Pointer variables are always declared with asterisk (*) appended to a variable.
  • The data type can be int, char, float, long and double.

Pointer Variable Examples

example
int *iptr; //Integer Pointer variable
long int *iptr; //long int Pointer variable
char *iptr; //char Pointer variable

Addressing Pointer Variables

addressing
int i = 5;
int *iptr; //Declaring pointer variable
iptr = &i ; //Initializing address of variable i to pointer variable iptr

The above segment illustrates that, the pointer variable is initialized by an address of integer variable i.

Dereferencing Pointer Variable

Dereferencing is an operation performed to access the value at particular address pointed to by a pointer. The operator * is used to returns the value stored at particular address. The operator * is known as value at address operator or dereferencing operator or indirection operator.

Program - Pointers

pointers.c
#include <stdio.h>
#include .<string.h>
int main()
{
int i = 5;
int *iptr;
iptr = &i;
printf("Value of i = %d ", i);
printf("\nAddress of i = %u", &i);
printf("\nValue of iptr = %d ", *iptr);
printf("\nAddress of iptr = %u", &iptr);
return 0;
}
  • Value of i = 5
  • Address of i = 65522
  • Value of iptr = 5
  • Address of iptr = 65526

Note:

  • The program illustrates the declaration of pointer i.e) *iptr.
  • Initialization of pointer i.e) iptr = &i;.
  • Clearly, the address of variable i is assigned to pointer variable iptr i.e) Value of iptr is nothing more than the address of i.
  • To access the value 5 using pointer variable iptr, we have to append * infront of a pointer variable i.e) *iptr.
  • To access the address of pointer variable, then we have to append & infront of a pointer variable i.e) &iptr.

Advantage of pointer

  • Without pointers, dynamic memory allocations are impossible.
  • When data type of particular data is unknown, then pointer can be used to access the data regardless of data types as pointers holds only address which is of integer data type.
  • Pointers are not just to refer existing variable with its address. Pointers are to interact directly with the hardware, simply one cannot write a data to the device drive without using pointers.
  • Pointers can be used to change the value permanently to a variable because pointer access the address of a variable.
  • Pointer provides an alternate way to access array elements.
  • Pointers are used to create complex data structures.

Disadvantage of pointer

  • Pointers are unsafe because its easy for a pointer to get you wrong.
  • Uninitialized pointers will cause segmentation fault.
  • Improper handling of pointers in dynamic memory allocation will leads to memory leaks.
  • Its very hard to debug pointer issues. So using pointers effectively will reduce head ache.
  • Though pointer syntax looks awesome i.e) *ptr. when you start appending more asterisks with pointer variable will makes you insane.
  • Pointers are 2X time slower than normal variables.

Did You Know?

Asterisks( * ) and address( & ) of operators are similar to positive and negative in mathematical point of view, which means appending * and & simultaneously to the pointer variable will cancelled by itself and just returns the address stored in it.
i.e) *( &iptr ) == iptr

Program - Asterisks and Address of Operators in Pointer Variable

pointers-asterisk.c
#include <stdio.h>
#include .<string.h>
int main()
{
int i = 5;
int *iptr;
iptr = &i;
printf("\nAddress of i = %u", &i);
printf("\nAddress of iptr = %u", &iptr);
printf("\nAddress of i = %u", *&iptr);
return 0;
}
  • Address of i = 65522
  • Address of iptr = 65526
  • Address of i = 65522

Note:

In the above program, third printf make sense. Simply asterisks( * ) and address( & ) of operators cancelled each other.

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