Pointers

Mr. Santosh N. Nagargoje

Introduction

• each variable you declare in your program will assign a location in the computer's memory.
• The value, the variable stores is actually stored in the location assigned.
• & (reference) operator gives you the address occupied by a variable.
• used to access the memory and manipulate the address.
• can assign and de-assign any space in the memory as you wish.

Why Pointers?

• Accessing array elements
• Passing arguments to a function when the function needs to modify the original argument
• Passing arrays and strings to functions
• Obtaining memory from the system
• Creating data structures such as linked lists

Pointer Variable

• variables that points to a specific address in the memory pointed by another variable.
• Syntax:��

data_type *pointer_variable_name; //declaration

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pointer_variable_name = &variable_name; //storing an address of a variable

int *a //pointer to integer

float *b //pointer to float

char *n //pointer to character

Distance *dn //pointer to Distance class

Accessing the variable pointed to

* - dereference operator

// accessing the variable pointed to�#include <iostream>�using namespace std;�int main()�{�int var1 = 11; //two integer variables�int var2 = 22;

int* ptr; //pointer to integers�ptr = &var1; //pointer points to var1�cout << *ptr << endl; //print contents of pointer (11)�ptr = &var2; //pointer points to var2�cout << *ptr << endl; //print contents of pointer (22)�return 0;�}

Pointers and Arrays

• Arrays are using implicit pointers.
• Ways to use pointers in arrays

//using index

for(){

* (array_variable_name + index );

}

//using pointer variable

pointer_to_array = array_variable_name;

for(){

* (pointer_to_array ++ );

}

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Pointers & Functions

Pass by reference:

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Pass by Pointers:

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return_type function_name(data_type&); //function prototype

function_name(variable) ; //function call

return_type function_name(data_type& variable){

//function definition

}

return_type function_name(data_type*); //function prototype

function_name(&variable) ; //function call

return_type function_name(data_type* variable){

//function definition

}

Passing Arrays

return_type function_name(data_type *); //prototype

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function_name(array_variable); //function call

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return_type function_name(data_type* pointer_variable_name){

//function definition

for(){

*pointer_variable_name++;

}

}

Memory Management: new and delete

• obtains memory from the operating system and returns a pointer to its starting point.
• pointer = new data_type;
• Syntax

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Memory Management: new and delete

• returns memory to the operating system.
• Syntax:

delete[] ptr; //deletes block of data

delete ptr //deletes single data