// Demonstrates calling a static member function through a plain C function pointer.

#include <stdio.h>
#include <stdlib.h>

extern "C" {
  typedef struct _p_Bar *Bar;
  struct _p_Bar {
    void *ctx;
    int (*fp)(int,void*);
  };
  int BarSetCallback(Bar b,int (*fp)(int,void*),void *ctx) {
    b->fp = fp;
    b->ctx = ctx;
    return 0;
  }
  int BarCall(Bar b,int x) {
    return b->fp(x,b->ctx);
  }
}

class Foo {
public:
  Foo(int x) : mystate(x) {};
  int SetupBar(Bar b) {
    return BarSetCallback(b,this->Function,this);
  }
  static int Function(int a,void *ctx) {
    // No "this" in static functions, but "p" serves the same purpose here
    Foo *p = (Foo*)ctx;
    return a + p->mystate;
  }
private:
  int mystate;
};

int main(void) {
  Foo f1(1),f2(2);
  Bar b = (Bar)malloc(sizeof(*b));
  // One way to set the callback
  BarSetCallback(b,f1.Function,&f1);
  printf("f1 10: %d\n",BarCall(b,10));

  // A different way
  f2.SetupBar(b);
  printf("f2 20: %d\n",BarCall(b,20));

  free(b);
  return 0;
}