Macros for easy generic creation of lists in C

list-example.c

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

DEFINE_LIST(int); /* defines the int_list type */

int main(void) {
  int_list *lst = EMPTY;
  PUSH(8, &lst, int_list);
  PUSH(4, &lst, int_list);
  PUSH(5, &lst, int_list);
  printf("popping value: %d\n", POP(&lst, int, int_list));
  printf("popping value: %d\n", POP(&lst, int, int_list));
  
  FREE_LIST(lst, int_list);
  
  if (lst == EMPTY) puts("the list has been freed");
  
  exit(EXIT_SUCCESS);
}

list.h

#ifndef __list_h
#define __list_h
#define EMPTY NULL

/* defines a list with the name TYPE_list.
   example: DEFINE_LIST(int); will make an int_list struct */
#define DEFINE_LIST(__head_t) \
  typedef struct __head_t##_list { \
    __head_t head; \
    struct __head_t##_list *tail; \
  } __head_t##_list

/* fres a list of any kind, 
   __lst is the list and __lst_type is the type of the list */
#define FREE_LIST(__lst, __lst_type) ({ \
  __lst_type *tail, *current = __lst; \
  while (current != EMPTY) { \
    tail = current->tail; \
    free(current); \
    current = tail; \
  } \
  __lst = EMPTY; \
})

/* pushes a new value into the list,
   __lst_type is the type of list, not type of head */
#define PUSH(__value, __lst, __tail_type) ({ \
  __tail_type *temp = malloc(sizeof(__tail_type)); \
  temp->head = __value; \
  temp->tail = *__lst;  \
  *__lst = temp; \
})

/* pops a value from the list and returns it */
#define POP(__input, __head_type, __tail_type) ({ \
  __tail_type *temp = *__input; \
  __head_type result; \
  if (temp->tail != EMPTY) { \
    result = temp->head; \
    temp = temp->tail; \
  } \
  else { \
    result = temp->head; \
    temp = EMPTY; \
  } \
  *__input = temp; \
  result; \
})
#endif