/*  File: fptr4.c

    Exploring function pointers.
*/

#include <stdio.h>

/* Define a type for pointers to functions that take a void * ptr 
   and returns nothing.
*/
typedef void (* FPTR_TYPE) (void *) ;

/* some simple functions */

void add3(int *iptr) {
   *iptr = *iptr + 3 ;
}


void add5(double *dptr) {
   *dptr = *dptr + 5.0 ;
}


/* Takes a function parameter */

void apply (FPTR_TYPE addx, void *rptr) {
   
  addx(rptr) ;
}


main() {
   int m = 2, n = 4 ;
   double x = 5.0 ;
   FPTR_TYPE fptr ;

   printf("&x = %x\n", &x) ;
   printf("&m = %x\n", &m) ;
   printf("&n = %x\n", &n) ;
   printf("\n") ;

   add3(&m) ;
   printf("After add3(&m), m = %d\n", m) ;

   add5(&x) ;
   printf("After add5(&x), x = %lf\n", x) ;
   printf("\n") ;

   apply((FPTR_TYPE) &add3, &m) ; // typecast &add3
   printf("Applying add3 to m, m = %d\n", m) ; 
   apply((FPTR_TYPE) &add5, &x) ;
   printf("Applying add5 to x, x = %lf\n", x) ; 
   printf("\n") ;

   fptr = (FPTR_TYPE) &add3 ;
   (*fptr) (&m) ; 
   printf("Applying fptr to m, m = %d\n", m) ; 
   fptr = (FPTR_TYPE) &add5 ;
   (*fptr) (&x) ; 
   printf("Applying fptr to x, x = %lf\n", x) ; 

   /* Bad behavior follows, fptr points to add5 */
   (*fptr) (&m) ;
   printf("Applying fptr to m, m = %d\n", m) ; 
   printf("n = %d\n", n) ;
}