// demofp3.cpp - demonstrate function pointer communication

#include <iostream>
using namespace std;

//////////////////////////////////////////////////////////
//  module using function pointers defines the callback //
//  signature and the function(s) using callbacks       //
//////////////////////////////////////////////////////////

// declare a funPtr type taking a void* argument

typedef void(*funPtr)(void* dptr);

void fun1(funPtr fptr, void* dptr) {  // this is function using
                                      // callback argument
  cout << " fun1 calling ";
  fptr(dptr);                  // invoke the function pointed to
}                              // note that this module doesn't
                               // know what fptr does nor its
                               // input data structure

///////////////////////////////////////////////////////////////
//  client code defines the callback functions and contents  //
//  of their calling parameter(s)                            //
///////////////////////////////////////////////////////////////

// client supplied callback input data
struct myStruct {
  int x;           // it can hold anything the design needs
  double y;
};

// client supplied callback function
void fun2(myStruct* ms) {
  cout << "fun2(myStruct* ms)\n"
       << "    ms->x = " << ms->x << "\n"
       << "    ms->y = " << ms->y << "\n";
}

int main() {

  cout << "\n\ndemonstrating callback communication\n\n";

  myStruct ms = { 1, 2.5 };
  funPtr callback;            // declare a function pointer

  callback = (funPtr)fun2;
  fun1(callback, (void*)&ms); // pass the function pointer, argument
                              // cast is necessary

  cout << "\n\n";
  return 0;
}