3.A way through the pointer (p.part 2)

Now we have the ability to store the address of a variable in a separate variable know as pointer variable and through that variable we can easily access the value of other variable whose address it is storing.(If you found this statement confusing you probably should give another good read to this article.)  

In this article we would try to break inside the variable using various ways.

Let’s take a look at the following code:-

1. #include<stdio.h>
2. void main()
3. {
4.                 int var;
5.                 int *p;
6.                 var=5;
7.                 p=&var;
8. }

After the execution of the above code this is how your machine will allocate memory space for both the variable var and p and put 5 inside var and address of var which happens to be 1000 inside p and as p is a pointer variable it acts as if the variable p is pointing towards the variable ‘var’.

While in reality it is just a variable (a space allocated inside the memory of your machine) that is why the pointer variable p will also have an address.

 Now let’s begin with the quest of figuring out multiple ways to access the address od variable the data contained in the variable etcetera etcetera.

First and the easiest way is to directly use the name of the variable :

printf(“%d”,var);

above piece of code will give the output :5 (the value inside the box named ‘var’).

and to know the address of the variable ‘var’ we can to use the &-operator(address-of  operator) as the name suggests it will help us to get the address of the variable nothing too tricky here:

printf(“%u”,&var);

above code will give the output:1000 (the address of ‘var’).

NOTE:-Here I have use %u as the format specifier to print the address. %u is the format specifier for  unsigned integer. This is usually used to print addresses because it’s range only has positive values making the range very large and usually addresses are positive integer number.

Second way ……before discussing about the second way lets give a quick visit to the world of special sticky note pads which has the address written down of your friend’s house.(If you need a brush up click here)

Now from here you can do two things first you can read the address and go near your friends address and stand outside the door from the sticky note pad or secondly you can read the address and visit your friends house and get inside the house.

If and only if you enter the house you would get to know whether your friend is inside the house of not or whether any another person is inside the house or not.

so if you try to output the value of ‘p’ by

printf(“%u”,p);

the output will be:1000 (the contain of the box of the variable p which is equal to the address of ‘var’)

so printing ‘p’ is as good as reading out the address from sticky note and standing outside of the memory location of ‘var’ so there is no way you would be able to know the content of ‘var’.

So now the moment has come to get inside ‘var’ and get the value which it contains so we once again use our special symbol ‘*’ to get inside ‘var’.

So the second way is:

printf(“%d”,*p);

the output will be :5 (The value at the address pointed or contained in the pointer variable ‘p’).

Few Graphical illustration will clear out everything:-

This is you

1.When

printf(“%d”,var);

you are at:

2.when

printf(“%u”,&var);

you are at:

3.when

printf(“%u”,p);

you are at:

4.When

printf(“%d”,*p);

you are at:

Lastly you can even get to know the address of the pointer variable p.

Do you know how?

if yes comment down the answer in the comment section below.

Thank You.