(
* Function
Pointer )
Hello
Friends,
Today I am going to discuss about function pointer.
OVERVIEW
:
What
is Pointer to function?
Just
like pointer to variable, pointer to array and pointer to structure, we can also have pointer to function. We can say that function
will be stored somewhere inside memory and we can declare pointer to
that function.
DECLARATION
:
We
can declare function pointer same as declaration of simple function.
Suppose we have function add() which takes int a and int b
as parameters and it returns
integer value. And we want to declare pointer to this function. So we
can do it this way :
suppose
function is,
int
add(int
a,int
b)
{
return
a+b;
}
and
now we will declare pointer to this function . . .
void
main()
{
int
(*ptr_func) ( int
, int
);
ptr_func
= &add;
//
this will also work
ptr_func
= add;
}
steps
to create function pointer :
1)
first of all write return type of function. -> int
2)
then write name of pointer in '( )' -> int (*ptr_func)
3)
then write type of arguments -> int (*ptr_func)
(int,int)
Third
step is not necessary so we can also write
int
(*ptr_func) ( )
but
it's a good habit to write argument types.
PROGRAMs on function pointer:
Now
let's see some programs on function pointer.
1). Passing function as a parameter
#include
<stdio.h>
int
add(int a,int
b,void (*ptr2) ( ) )
{
ptr2(
); //calling func
return
a+b;
}
void
func()
{
printf("Addition
!!\n");
}
void
main()
{
int
ans;
int
(*ptr1) ( ) = add; //pointer to function add
ans
= ptr1( 3 , 4 , func ); //passing func as
parameter
printf(
" ANS : %d \n ", ans );
}
o/p
:
Addition
!!
ANS
: 7
Explanation
:
This was a very simple example to understand passing of function as a parameter.
But
here you may have one question. Why do we need to pass function as a parameter?
Because in this program use of function pointer doesn't make sense. best example for this is library function qsort().
For
small program like this, this seems to be unnecessary.
2).
we can made array of pointer to function.
Before
going for this program let's see another one.
This
is program for simple calculator.
#include <stdio.h >
int
add (int a ,
int b) { return a+b; }
int
sub (int a , int
b) { return a-b; }
int
mul (int a , int
b) { return a*b; }
int
div (int a , int
b) { return a/b; }
void
main()
{
int
input, ans;
printf("1.
Add \n 2. Substract \n 3. Multiply \n 4. Divide \n 5. Exit \n Enter
Your Choice : ");
scanf("%d",&input);
switch(input)
{
case
1:
ans
= add( 3 , 4 );
break;
case
2:
ans
= sub ( 3 , 4 );
break;
case
3:
ans
= mul ( 3 , 4 );
break;
case
4:
ans
= div( 3 , 4 );
break;
default:
break;
default:
break;
}
printf(“ANS
: %d \n ”, ans );
}
Now
let's use array of function pointer for the same program.
#include <stdio.h >
int
add (int a ,
int b) { return a+b; }
int
sub (int a , int
b) { return a-b; }
int
mul (int a , int
b) { return a*b; }
int
div (int a , int
b) { return a/b; }
void
main()
{
int
input, ans;
int
(*ptr_fun [4] ) ( int , int
) = { add, sub, mul, div };
printf("1.
Add \n 2. Substract \n 3. Multiply \n 4. Divide \n 5. Exit \n Enter
Your Choice : ");
scanf("
%d ", &input );
ptr_fun
[input-1] ( 3 , 4 ); //replacing whole switch
case !!!
}
Just
like array of pointer we have array of pointer to function.
So
this way we can replace switch case with only a single line.
- typedef WITH FUNCTION POINTER :
As
we know typedef is used for simple naming convention, we can use it
for function pointer to make it more easy to read. When we have more
than one function having same return type and same parameters we can
make a simple way of declaring pointer to this function.
Suppose
we want pointer to function for all functions add, sub, mul and div ,
we can do it like this,
int
(*ptr1_fun) (int, int) = add;
int
(*ptr2_fun) (int, int) = sub;
int
(*ptr3_fun) (int, int) = mul;
int
(*ptr4_fun) (int, int) = div;
now
let's make it simple using typedef.
typedef
int (*ptr_fun ) ( int , int);
now
we can use ptr_fun to declare new pointers to function having return type
integer and both parameters also integer.
ptr_fun
ptr1 =add;
ptr_fun
ptr2 = sub;
ptr_fun
ptr3 = mul;
ptr_fun
ptr4 = div;
OHH!! It looks very clean.
Thanks,
Akash Patel
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http://letsmakeceasy.blogspot.in/2014/09/pointer-in-c.html
http://letsmakeceasy.blogspot.in/2014/09/array-in-c.html
Link for Preprocessor in C :
http://letsmakeceasy.blogspot.in/2014/09/preprocessor-directives.html
