Pointers to Functions

POINTERS TO FUNCTIONS

A function like a variable, has an address location in the memory. It is therefore, possible to declare a pointer to a function, which can then be used as an argument in another function. A pointer to a function is declared as follows:

type ( * fp) ( ) ;

This tells the compiler that fp is a pointer to a function which returns type value.
We can make a function pointer to point to a specific function by simply assigning the name of the function to the pointer.

For example

double (*P1)( ), mul ( ) ;

P1 = mul ;

declare P1 as a pointer to a function and mul as a function and then make P1 to point to the function mul. To call the function mul, we may now use the pointer P1 with the list of parameters.

That is,

(*P1) (x,y)
is equivalent to mul ( x,y )


FUNCTIONS RETURNING POINTERS

The way functions return an int, a float, a double or any other data type, it can even return a pointer. However, to make a function return a pointer it has to be explicitly mentioned in the calling function as well as in the function declaration.

The following program illustrates this

main ( )

{

int * P ;

int * fun ( ) ;

P = fun ;

printf ( “\n % Id”, P ) ;

}

int * fun ( )

{

int i = 20;

return (& i) ;

}
In this program, function fun( ) is declared as pointer returning function can return the address of integer type value and in the body of the function fun ( ) we are returning the address of integer type variable i into P which is also integer type pointer.