X Macros Example

x_macros_example.c

#include <stdio.h>

// void/void function wrapper to make code readable.
typedef void (*runnable_t)();

// Animal functions definitions.
void bark() {
  printf("Guau!\n\r");
}

void mew() {
  printf("Miau!\n\r");
}

void croak() {
  printf("Ribit!\n\r");
}

// Animal groups declaration.
typedef enum {
  MAMMAL,
  AMPHIBIAN
} animal_group_t;

// Table associating animals with their sounds.
#define ANIMAL_TABLE(XX) \
  XX(DOG, MAMMAL, bark) \
  XX(CAT, MAMMAL, mew)  \
  XX(FROG, AMPHIBIAN, croak)

// Definition of animal type.
typedef enum animal {
#define XX(animal, group, onomat) animal,
  ANIMAL_TABLE(XX)
#undef XX
 ANIMAL_N
} animal_t;

// Definition of animal functions table.
runnable_t animal_functions[] = {
#define XX(animal, group, onomat) onomat,
  ANIMAL_TABLE(XX)
#undef XX
};

// Animal Groups definitions.
animal_group_t animal_groups[] = {
#define XX(animal, group, onomat) group,
  ANIMAL_TABLE(XX)
#undef XX
};

// Test main
int main() {

  if(animal_groups[DOG] == MAMMAL) {
    animal_functions[DOG]();
  }

  if(animal_groups[FROG] == AMPHIBIAN) {
    animal_functions[FROG]();
  }

  if(animal_groups[CAT] == AMPHIBIAN) {
    animal_functions[CAT]();
  } else {
    printf("Hey! Cats aren't amphibians");
  }
  
}