Pointers in C

C Programming, Free C Language Tutorials.
C Programming, Free C Language Tutorials.

In this tutorial I am going to discuss what pointer is and how to use them in our C program. Many C programmer thinks that pointer is one of the difficult topic in C language but it’s not completely true. It is difficult to understand in comparison of other secondary (array, structure etc.) data types available in C. Pointer in C seems to be difficult because it works directly with computer memory (RAM).

When we declare any variable in C, for example integer variable, it occupies a memory according to its size (here 2 bytes). As it occupies a memory so it’s natural to have an address for this location so that it can be referenced later by CPU for manipulation. But before we begin with Pointer we must have some idea on the operators we are going to use in Pointer programming.

The ‘*’ And ‘&’ Operators

Take a look on the following declaration,

                int x=10;

When we make such declaration how C compiler treat this statement:

  1. Reserve memory space for this integer value.
  2. Name this memory location as x.
  3. Store the value 10 at this location.

This can be illustrated by a simple diagram:

Integer variable location in memory.
Integer variable location in memory.

So when we declared an integer variable x and assigned value 10 then compiler occupied a 2 byte memory space at memory address 65325 and stored value 10 at that location. Compiler named this address x so that we can use x instead of 65325 in our program. But we can use address or variable in our program and both will point to the same value (example given below).

The memory address of a variable could differ from PC to PC and entirely depends on available free space in memory at time of program execution. As this differs from PC to PC thus we cannot rely on that address (numeric value representing variable address) and we cannot use this address in our program. But have you noticed one thing that address is an integer.

We can print address of any variable or function, following program shows how we can do that:

Address of variable example.

#include<stdio.h>
#include<conio.h>

void main()
{
	int i=9;
	clrscr();

	printf("Value of i : %d\n",i);
	printf("Address of i : %u",&i);

	getch();
}

This is a very simple c program which prints value and address of an integer. But did you notice line no. 10 in above program? This line output the address of i variable and to get address of i variable we have used ampersand (&) operator. This operator is known as "Address of" operator and we already used this operator many times in our program, just recall scanf statement which is used to accept input from computer keyboard. So when we use ampersand operator (&i) before any variable then we are instructing c compiler to return its address instead of value.

Another operator we going to deal with in this entire pointer tutorial is "*" called "Value at address" operator. It is the same operator which we use for multiplication of numbers. As the name suggest, "value at address" operator returns value stored at particular address. The "value at address" operator also called indirection operator. Following example extends above C program and puts "value at address" operator in action.

Value at address (*) example

#include<stdio.h>
#include<conio.h>

void main()
{
	int i=9;
	clrscr();

	printf("Value of i : %d\n",i);
	printf("Address of i : %u\n",&i);
	printf("Value at address of i : %d",*(&i));

	getch();
}
Output of "value at address" operator example.
Output of "value at address" operator example.

Now in this program notice line no. 11 and use of ‘&’ and ‘*’ operators also see the output of program which prints value of variable i and *(&i) same. This is how these two operator works.

You must have clear idea of ‘&’ and ‘*’ operator usage before you jump into pointer because pointer deals with these to operator. If you find any difficulty then post your doubts and I will try to clear your doubts.

What is Pointers in C Programming?

A pointer is a secondary data type (also known as derived data type) in C. It is built from one of the primary data types available in C language. Basically pointer contains memory address of other variable or function as their value. As pointer deals with memory address, it can be used to access and manipulate data stored in memory.

Benefits of using Pointer in C Program

Pointer is one of the most exciting features of C language and it has added power and flexibility to the language. Pointer is in C language because it offers following benefits to the programmers:

  1. Pointers can handle arrays and data table efficiently.
  2. Pointers support dynamic memory management.
  3. Pointer helps to return multiple values from a function through function argument.
  4. Pointer increases program execution speed.
  5. Pointer is an efficient tool for manipulating structures, linked lists, queues stacks etc.

We can achieve these and much more benefits from pointer only if we can use it properly.

Pointer with an example

Since this tutorial is already become lengthy so I am going to give a small example on how we can use pointer in our C program. Of course we will discuss remaining part in my next pointer tutorial.

Syntax:            datatype *pointer_name;

Example :        int *iPtr;

                        float *fPtr;

Pointer Example

#include<stdio.h>
#include<conio.h>

void main()
{
	int i=9, *ptr;
	ptr=&i;
	clrscr();

	printf("Value of i : %d\n",i);
	printf("Address of i : %u\n",&i);
	printf("Value of ptr : %u\n",ptr);
	printf("Address of ptr : %u\n",&ptr);
	printf("Ptr pointing value : %d", *ptr);

	getch();
}

In the above example in line no. 6 we have declared an integer i and assigned 9 to it. Along with variable i, we have also declared an integer pointer. To declare a pointer of any data type we just need to put an * (asterisk) before variable name or identifier. In our example ptr is an integer variable and is capable of holding address of any integer variable.

Remember one thing integer pointer can hold only integer variable address, you cannot use integer pointer to hold address of float or char variable. To hold char or float variable address in a pointer you need to declare char or float pointer respectively.

In line no. 7 we assigned integer variable i’s address to ptr, now ptr is pointing to i. Line no 10 prints value of i and line no. 11 prints address of i. Next line prints value stored in ptr pointer variable, line no. 13 prints address of ptr pointer. As pointer is different entity so it also requires space in memory. Memory occupied by a pointer depends on its data type. Integer pointer will occupy 2 bytes whereas character pointer will occupy 1 byte. Finally line no. 14 prints the value of address stored in ptr pointer i.e. value of i. And to print value of stored address in a pointer we need write *pointer variable name (in our example *ptr). A memory map will help you to understand this.

Pointer memory map.
Pointer memory map.
Pointer example output.
Pointer example output.

If you find any difficulty or error in this article then please let me know through comment box.

Thank you for visiting my free C pointer tutorial. 

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41 comments

puspak 7 years ago

it is awesome


nekros729 profile image

nekros729 7 years ago

Haha, the title confused me a little bit, I thought you were talking about tips. I'm always up for improvement. =)


nicomp profile image

nicomp 6 years ago from Ohio, USA

%p also works as a print format for a pointer. A memory address is not, strictly speaking, an integer data type. It may be a segment/offset combination, or some other data structure. Specific information is a function of the computer architecture on which the C program is executing.

int x;

x = 123;

printf("%p", (void *)&x); // prints the address of the integer x


Brad Masters 6 years ago

Very nice presentation

How about a comparison

C, C++, C#

doing the same thing.


k.rajesh 6 years ago

c commandas used in c++


subhash sharma 6 years ago

ur effort realy very effective , what nice explain pointer


gauri1234 profile image

gauri1234 6 years ago

you have covered a lot..i wished too but "u well done"


rekha 6 years ago

i want to improve programming in pointers.so please guide me in programming.


shruti singh 6 years ago

nice presentation for basic concept, but need more to be expalined for implementation


Madhavi Devineni 6 years ago

Hi! This is Madhavi

Your Pointers topic is nice. But, I could not understand, "How the pointer and arrays are the datatypes?"


mudd 6 years ago

it is just AWESOME.. you really are a genius because you know how to break down this type of topic into the basic of basics for first time programmers like me.. i just couln't understand the way my instructor taught this to our class..such a bummer

thanks again!


Manish Arya 6 years ago

this methode is too good very much for understand the pointer....anybody


jalesingh 6 years ago

Its OK but I want more examples on C pointer.


sambaran08 profile image

sambaran08 6 years ago from India

Very nice,but next time explain step by step with many example,

visit my blog http://hubpages.com/technology/Cnet

and follow me


Blake 6 years ago

Awesome post, but one point is not quite accurate. You mentioned that "Memory occupied by a pointer depends on its data type. Integer pointer will occupy 2 bytes whereas character pointer will occupy 1 byte." This is not true. All pointers occupy the same amount of space on a given platform, regardless of the data type to which they point. For example, on a 32-bit system, a pointer will occupy 4 bytes of memory. On a 64-bit system, a pointer will occupy 8 bytes of memory. This is true regardless of whether the pointer points to an int, char, float, or any other type of data.


PARIJAT 5 years ago

WHAT IS SHORT-CIRCUIT STATEMENT IN C????


leena 5 years ago

really ur work is so good..... well done......but we want more on "MACROS"


surya 5 years ago

thax for ur pointers concept,now i am clear about pointers.


aruna 5 years ago

its vry gud explanations


sunil 5 years ago

lol

but i need some array pointer


ronel 5 years ago

thanks!! this is useful


Santosh Kedar 5 years ago

Thank u sir..............


javgal-shimoga 5 years ago

thumba dhanyavaadagalu - artha vayithu !

i was hoping you could give an example on "structure in a structure " in your blog .

thank you

-

javgal -benglooru


Mr. Amit Shaw 5 years ago

#include

void main()

{

clrscr();

printf("This Site is Just Awesome /n");

printf("Thanks Thank you Very Much Admin");

getch();

}


rajkishor09 profile image

rajkishor09 5 years ago from Bangalore, Karnataka, INDIA Author

@Mr. Amit Shaw: i like your way of appreciation. Thanks buddy


Logasubramaniyam 5 years ago

why we are using %u what is the use of it?will u help pls


Gautham 5 years ago

Helpful.


mahendrababu 5 years ago

u hv done a good job


manjot 4 years ago

a good suggestion buddy ask ques related to topics also


Musau 4 years ago

Excellent tutorial especially for beginners


Manthabi 4 years ago

This is gorgeous. For the first time I'm beginning to understand the concept of pointers


goldi 4 years ago

its sufficient to beginners,but i confuse of this Q. i.e. how many types of pointer?


AJIT 4 years ago

IT QUIT HELP ME A LITTLE BIT BUT OVER ALL HELP FULL. THANK U


mohammed ali 4 years ago

good i have well understood


some guy.. ^^ 4 years ago

The title really is confusing. At the first glance I thought it would be pointers as in GUIDE but since I have knowledge in programming, I was able to easily adapt with the idea.

Layout is great, lots of ads but not overcrowded unlike most of blogs I have seen ^__^


bhavani lalitha 4 years ago

very nice and u can give a lot of information thank you so much


Thiva 4 years ago

Thanx..help me to understand * and & in pointers.


sriman 4 years ago

thanqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq sirrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr


Umang 4 years ago

Very Good For who have start learn of Pointer


4 years ago

segment of program displays the contents of variables X and Y. Add two more lines of code to print the address of the two variables using the address operator.

int X = 5, Y = 10;

printf(“The value of X: %d\n”, X);

printf(“The value of Y: %d\n”, Y);


Akshay 3 years ago

What is the meaning of

ptr**

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