雑な実装のスタックとキュー 下手なこと(空に対しての操作とか)するとバグるはず

queue.c

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

typedef long item;

typedef struct {
  int max_size;
  int head, length;
  item *items;
} queue;

int q_index(queue *q, int i) {
  return i & ((1<<q->max_size)-1);
}

item front(queue *q) {
  return q->items[q_index(q, q->head)];
}

item back(queue *q) {
  return q->items[q_index(q, q->head+q->length-1)];
}

void pop(queue *q) {
  q->head++;
  q->length--;
}

void push(queue *q, item v) {
  q->length++;
  if (q->length > (1<<q->max_size)) {
    q->max_size++;
    q->items = realloc(q->items, sizeof(item)*(1<<q->max_size));
  }
  q->items[q_index(q, q->head+q->length-1)] = v;
}

/// new_size(size).max_size == 2**size
queue new_size(int size) {
  queue q = { 1<<size, 0, 0, NULL };
  q.items = malloc(sizeof(item)*(1<<q.max_size));
  return q;
}

queue new(void) {
  return new_size(4);
}

void print_queue(queue *q) {
  printf("(max_size = %d, head = %d, length = %d){"
    , q->max_size, q->head, q->length);
  if (q->length)
    printf(" %ld", front(q));
  for (int i = q->head+1; i < q->head+q->length; i++)
    printf(", %ld", q->items[q_index(q, i)]);
  printf(" }\n");
}

int main(void) {
  queue q = new();
  print_queue(&q);
  for (int i = 0; i < 16; ++i)
    push(&q,i);
  print_queue(&q);
  for (int i = 0; i < 8; ++i)
    pop(&q);
  print_queue(&q);
  push(&q,0);
  push(&q,1);
  print_queue(&q);
}

stack.c

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

typedef long item;

typedef struct {
  int max_size;
  int size;
  item *items;
} stack;

item top(stack *s) {
  return s->items[s->size-1];
}

void pop(stack *s) {
  s->size--;
}

void push(stack *s, item v) {
  s->size++;
  if (s->size > s->max_size) {
    s->max_size *= 2;
    s->items = realloc(s->items, sizeof(item)*s->max_size);
  }
  s->items[s->size-1] = v;
}

stack new_size(int size) {
  stack s = { size, 0, NULL };
  s.items = malloc(sizeof(item)*size);
  return s;
}

stack new(void) {
  return new_size(16);
}

void print_stack(stack *s) {
  printf("(max_size = %d, size = %d){", s->max_size, s->size);
  if (s->size >= 1)
    printf(" %ld", s->items[0]);
  for (int i = 1; i < s->size; ++i) {
    printf(", %ld", s->items[i]);
  }
  printf(" }\n");
}

int main(void) {
  stack s = new();
  print_stack(&s);
  for (int i = 0; i < 256; ++i)
    push(&s,i);
  print_stack(&s);
  printf("top = %ld\n", top(&s));
  for (int i = 0; i < 240; ++i)
    pop(&s);
  print_stack(&s);
}