class example

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

#define CLASS_METHOD                         \
  register unsigned long rbp __asm__("rbp"); \
  c_class *this = rbp + 16; // cfi_def_cfa_offset 16

typedef struct c_class
{
  int (*add)(void);
  int (*sub)(void);

  int a;
  int b;

} c_class;

int c_class_add(void)
{
  CLASS_METHOD

  return this->a + this->b;
}

int c_class_sub(void)
{
  CLASS_METHOD

  return this->a - this->b;
}

int main(void)
{
  c_class c =
  {
    .add = c_class_add,
    .sub = c_class_sub,
    .a   = 300,
    .b   = 200
  };

  printf("(expected 500) c.add() = %d\n", c.add());
  printf("(expected 100) c.sub() = %d\n", c.sub());

  return EXIT_SUCCESS;
}