Pointer
What is pointer in c programming?
Pointer is a user defined
data type which creates special types of variables. These variables can hold
the address of primitive data type like char, int, float, double or user
defined data type like function, pointer etc. or derived data type like array,
structure, union, enum.
Examples
of pointer variables:
int *ptr; // primitive data type
int (*ptr)(); // User defined data type
int (*ptr)[2]; // derived data type
In
c programming every variable keeps two type of value.
1.
Value of variable.
2.
Address of variable where it has stored in the memory.
(1)
Meaning of following simple pointer declaration and definition:
int a=5;
int *ptr;
ptr=&a;
Explanation:
About
variable a:
1. Name
of variable : a
2.
Value of variable which it keeps: 5
3. Address where it has stored in memory : 1025 (assume)
About variable ptr:
4. Name
of variable : ptr
5.
Value of variable which it keeps address of variable a: 1025
6. Address where it has stored in memory : 5000 (assume)
(2)
Meaning of following pointer declaration and definition (pointer to pointer):
int a=50;
int *ptr1,**ptr2;
ptr1=&a;
ptr2=&pt1;
Explanation:
About
variable a:
1.
Name of variable : a
2.
Value of variable which it keeps: 50
3. Address where it has
stored in memory : 5000 (assume)
About
variable ptr1:
4.
Name of variable : ptr1
5.
Value of variable which it keeps: 5000
6. Address where it has
stored in memory : 9000 (assume)
About
variable ptr2:
7.
Name of variable : ptr2
8.
Value of variable which it keeps: 9000
9.
Address where it has stored in memory : 9555 (assume)
Note:
*
is known as indirection operator which gives content of any variable
&
is known as reference operator which gives address
Cancellation
rule of above two operators:
* and
& operators always cancel to each other i.e. *&p=p
But it is not right to write: &*p=p
What
will be output of following c program?
#include<stdio.h>
#include<conio.h>
void main()
{
int x=25;
int *ptr=&x; //statement one
int **temp=&ptr; //statement two
printf(“%d%d%d”,x,*ptr,**temp);
getch();
}
Output: 25 25 25
Explanation:
As
we know value of variable x is 25.
*ptr=
*(&x) //from statement one
=*&x
=x
//using cancellation rule
=25
How to read complex pointers in C
Programming?
Assign the priority
to the pointer declaration considering precedence and associative according to
following table.
Where
():
This operator behaves as bracket operator or function operator.
[]:
This operator behaves as array subscription operator.
*:
This operator behaves as pointer operator not as multiplication operator.
Identifier: It is not an operator but it is name of pointer variable. You will
always find the first priority will be assigned to the name of pointer.
Data type: It is also not an operator. Data types also includes modifier (like signed
int, long double etc.)
You will understand
it better by examples:
(1) How to read following pointer?
char
(* ptr)[3]
Answer:
Step 1: () and [] have equal precedence. So rule of associative
will decide the priority. Its associative is left to right So first priority
goes to ().
Step
2: Inside the bracket * and ptr enjoy equal
precedence. From rule of associative (right to left) first priority goes to ptr
and second priority goes to *.
Step3: Assign third priority to [].
Step4: Since data type enjoys least priority so assign fourth priority to
char.
Now read it
following manner:
ptr is pointer to such one
dimensional array of size three
which content char type data.
