Pointers in C
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:
- Reserve memory space for this integer value.
- Name this memory location as x.
- Store the value 10 at this location.
This can be illustrated by a simple diagram:
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();
}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:
- Pointers can handle arrays and data table efficiently.
- Pointers support dynamic memory management.
- Pointer helps to return multiple values from a function through function argument.
- Pointer increases program execution speed.
- 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.
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.
C Programming Learner's Poll
Is this tutorial helpful to understand basic C Pointer concept?
C Programming Other Tutorial Links
- C Programming Function Pointer
Like C variables, function too has address and we can use this address to invoke function. So this tutorial is entirely devoted to function-pointer. But before we can call a function using we need to find out... - A Brief History of the C Language
Before we start any complex program in C, we must understand what really C is, how it came into existence and how it differs from other languages of that time. In this tutorial I will try to talk about these... - Data Types in C Language
A programming language is proposed to help programmer to process certain kinds of data and to provide useful output. The task of data processing is accomplished by executing series of commands called... - Array in C programming Programmer's view
An array in C language is a collection of similar data-type, means an array can hold value of a particular data type for which it has been declared. Arrays can be created from any of the C data-types int,... - How to work with Two Dimensional Arrays in C
We know how to work with an array (1D array) having one dimension. In C language it is possible to have more than one dimension in an array. In this tutorial we are going to learn how we can use two... - How to work with Multidimensional Array in C Programming
C allows array of two or more dimensions and maximum numbers of dimension a C program can have is depend on the compiler we are using. Generally, an array having one dimension is called 1D array, array... - Types of Function in C Programming Languages:
In my previous c programming tutorial I tried to explain what the function, its advantages is and how to declare a C function. And I told you that there are five types of functions and they are: ... - What is Function in C Language?
A function in C language is a block of code that performs a specific task. It has a name and it is reusable i.e. it can be executed from as many different parts in a C Program as required. It also ...
Comments
it is awesome
Haha, the title confused me a little bit, I thought you were talking about tips. I'm always up for improvement. =)
%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
Very nice presentation
How about a comparison
C, C++, C#
doing the same thing.
c commandas used in c++
ur effort realy very effective , what nice explain pointer
you have covered a lot..i wished too but "u well done"
i want to improve programming in pointers.so please guide me in programming.
nice presentation for basic concept, but need more to be expalined for implementation
Hi! This is Madhavi
Your Pointers topic is nice. But, I could not understand, "How the pointer and arrays are the datatypes?"
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!
this methode is too good very much for understand the pointer....anybody
Its OK but I want more examples on C pointer.
Very nice,but next time explain step by step with many example,
visit my blog https://hubpages.com/technology/Cnet
and follow me
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.
WHAT IS SHORT-CIRCUIT STATEMENT IN C????
really ur work is so good..... well done......but we want more on "MACROS"
thax for ur pointers concept,now i am clear about pointers.
its vry gud explanations
lol
but i need some array pointer
thanks!! this is useful
Thank u sir..............
thumba dhanyavaadagalu - artha vayithu !
i was hoping you could give an example on "structure in a structure " in your blog .
thank you
-
javgal -benglooru
#include
void main()
{
clrscr();
printf("This Site is Just Awesome /n");
printf("Thanks Thank you Very Much Admin");
getch();
}
- Author
@Mr. Amit Shaw: i like your way of appreciation. Thanks buddy
why we are using %u what is the use of it?will u help pls
Helpful.
u hv done a good job
a good suggestion buddy ask ques related to topics also
Excellent tutorial especially for beginners
This is gorgeous. For the first time I'm beginning to understand the concept of pointers
its sufficient to beginners,but i confuse of this Q. i.e. how many types of pointer?
IT QUIT HELP ME A LITTLE BIT BUT OVER ALL HELP FULL. THANK U
good i have well understood
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 ^__^
very nice and u can give a lot of information thank you so much
Thanx..help me to understand * and & in pointers.
thanqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq sirrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
Very Good For who have start learn of Pointer
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);
What is the meaning of
ptr**
41