queue sample program

Makefile

# Queue sample program
#  Author: Masayuki Ataka  <masayuki.ataka@gmail.com>
PROGRAM = queue

CC = gcc
CFLAGS = -W -Wall -g -O2 -std=c99
CPPFLAGS = -DDEBUG

all: $(PROGRAM)

$(PROGRAM): queue.o
	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ $^

queue.o: queue.c queue.h

#
# clean
#
RM = rm -f
clean:
	$(RM) *~
	$(RM) *.o

distclean: clean
	$(RM) $(PROGRAM)

queue.c

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include "queue.h"

/* ---------------------------------------- *\
   Function declaration
\* ---------------------------------------- */
static bool is_empty(const queue_t* const q);

/* ---------------------------------------- *\
   Functions
\* ---------------------------------------- */
queue_t* new_queue(void)
{
  queue_t* q = (queue_t*)malloc(sizeof(queue_t));
  if (q == NULL){
    fprintf(stderr, "Allocation Error: queue\n");
    return NULL;
  }
  q->tail = NULL;
  q->head = q->tail;

  return q;
}

/* Return TRUE if succeeded to malloc NEW node, else return FALSE. */
bool enqueue(const int n, queue_t* const queue)
{
  node_t* new = (node_t*)malloc(sizeof(node_t));
  if (new == NULL){
    fprintf(stderr, "Allocation Error: node\n");
    return false;
  }
  new->n = n;
  new->prev = NULL;

  if (is_empty(queue)){
    queue->tail = new;
  } else {
    queue->head->prev = new;
  }
  queue->head = new;

  return true;
}

/* Return 0 if queue is empty, else return dequeued value */
int dequeue(queue_t* const queue)
{
  node_t* last = queue->tail;
  if (is_empty(queue)){
    fprintf(stderr, "QUEUE is empty\n");
    return 0;
  } else {
    queue->tail = last->prev;
  }

  int n = last->n;
  free(last);
  return n;
}

void del_queue(queue_t* const queue)
{
  if (!is_empty(queue)){
      node_t* last = queue->tail;
      queue->tail = last->prev;
      free(last);
  }
  free(queue);
}

static bool is_empty(const queue_t* const q)
{
  return q->tail == NULL;
}


#ifdef DEBUG
/* ---------------------------------------- */
int main(void)
{
  queue_t* q = new_queue();

  enqueue(5, q);
  enqueue(4, q);
  enqueue(3, q);
  printf("%d\n", dequeue(q));
  printf("%d\n", dequeue(q));
  printf("%d\n", dequeue(q));
  // queue is empty

  // dequeue error check when queue is empty
  printf("%d\n", dequeue(q));

  enqueue(2, q);
  printf("%d\n", dequeue(q));
  // queue is empty

  del_queue(q);
  return 0;
}
#endif  /* DEBUG */

queue.h

#ifndef __QUEUE_H__
#define __QUEUE_H__

typedef struct node_tt
{
  struct node_tt* prev;
  int n;
} node_t;

typedef struct
{
  node_t* head;
  node_t* tail;
} queue_t;

queue_t* new_queue(void);
bool     enqueue(const int n, queue_t* const queue);
int      dequeue(queue_t* const queue);
void     del_queue(queue_t* const queue);

#endif  /* __QUEUE_H__ */