// demofp4.cpp - demonstrate more function pointer communication
//               using global variables to pass data
#include <iostream>

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

// declare a funPtr type taking no argument

typedef void(*funPtr)();

void fun1(funPtr fptr) {        // this is function using
                                // callback argument
  std::cout << "  fun1 calling ";
  fptr();                      // 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 - it's global
struct myStruct {
  int x;           // it can hold anything the design needs
  double y;
} ms = { 1, 2.5 };

// client supplied callback function
void fun2() {
  std::cout << "fun2() using global structure\n"
       << "    ms.x = " << ms.x << "\n"
       << "    ms.y = " << ms.y << "\n";
}

void main() {

  std::cout << "\n\n  Demonstrate callback communication\n\n";

  funPtr callback;       // declare a function pointer

  callback = (funPtr)fun2;
  fun1(callback);        // pass the function pointer, argument
                         // cast is necessary
  std::cout << "\n";
}