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Pointer is a memory variable that holds the address
of another variable, which is called pointing to variable. Using the pointer
variable the contents of the variable to which it is pointing can be accessed
directly & also can be changed. Pointers are declared using the ‘*’
as prefix operator.
Int *ptr;
the address of other variables can be assigned using
‘&’ prefix operator.
int i=30;
ptr=&i;
Here is the program to explain
the same.
| main()
{
int x=30;
int *ptr;
ptr=&x;
printf("\n x=%d",x);
printf("\n &x=%u",&x);
printf("\n ptr=%u",ptr);
printf("\n *ptr=%d",*ptr);
} |
values of the variable can
be modified to which the pointer is pointing.
| main()
{
int x=30;
int *ptrx=&x;
printf("\n before assignment x = %d",x);
*ptrx=20;
printf("\n After assignment x = %d",x);
} |
The datatype of the pointer
is not to specify the type of data pointer will be storing but to specify
to what datatype it will point in future. All the pointer variables are
of unsigned int type.
main()
{
int *iptr;
float *fptr;
char *cptr;
printf("\nSize of integer pointer is %d",sizeof(iptr));
printf("\n Size of float pointer is %d",sizeof(fptr));
printf("\n Size of char pointer is %d",sizeof(cptr));
} |
The above program shows though the pointers are of
different types, still all of them occupy the same space in memory i.e.
2 bytes. This proves that datatype of pointer is not to decide what pointer
is storing but to what it is pointing.
Call by reference
While we were learning User Defined functions we
have done an example on call by value, Here comes a method Call by Reference
which is related to that topic.
main()
{
int x=20,y=30;
printf("\n In main Function x = %d, y=%d",x,y);
swap(&x,&y);
printf("\n In main Function x = %d, y=%d",x,y);
}
swap(int *x,int *y)
{
int t;
t=*x;
*x=*y;
*y=t;
printf("\n In swap Function x = %d, y=%d",*x,*y);
} |
Here in this example instead of passing values of
variables we are passing the addresses of variables and they are stored
in pointer variables in function swap. Swap function uses these address
and modifies the contents of variables to which its pointing. So through
pointers we can change the contents of variables for swap purpose.
Other Topics that can
be done with pointers are like
( To maintain the syllabus concise & Simple
these topics are not explained here).
-
Pointers and Arrays.
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Pointer to pointer
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Dynamic Memory Allocation
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Direct Access to MS-DOS memory location
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