队列实例程序（C语言）

/* queue.h */

#ifndef _QUEUE_H
#define _QUEUE_H

struct queue_record;
typedef struct queue_record *queue;

int is_empty( queue q );
int is_full( queue q );
queue create_queue( int max_elements );
void dispose_queue( queue q );
void make_empty( queue q );
void enqueue( int x, queue q );
int front( queue q );
void dequeue( queue q );
int front_and_dequeue( queue q );

#endif

/* queue.c */

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

#define MIN_QUEUE_SIZE    5

struct queue_record
{
    int capacity;
    int front;
    int rear;
    int size;
    int *array;
};

void
make_empty( queue q )
{
    q->size = 0;
    q->front = 1;
    q->rear = 0;
}

int
is_empty( queue q )
{
    return q->size == 0;
}

int
is_full( queue q )
{
    return q->size == q->capacity;
}

queue
create_queue( int max_elements )
{
    queue q;

    if( max_elements < MIN_QUEUE_SIZE )
    {
        printf("Queue size is too small!\n");
        exit(0);
    }

    q = malloc( sizeof(struct queue_record) );
    if(q == NULL)
    {
        printf("Out of space!\n");
        exit(1);
    }
    q->array = malloc(sizeof(int) * max_elements);
    if(q->array == NULL)
    {
        printf("Out of space!\n");
        exit(1);
    }
    q->capacity = max_elements;

    make_empty(q);

    return q;
}

static int
succ( int value, queue q )
{
    if( ++value == q->capacity )
        value = 0;
    return value;
}

void
enqueue( int x, queue q )
{
    if( is_full( q ) )
    {
        printf("full queue!\n");
        exit(0);
    }
    else
    {
        q->size++;
        q->rear = succ( q->rear, q );
        q->array[q->rear] = x;
    }
}

void
dequeue( queue q )
{
    if( is_empty( q ) )
    {
        printf("empty queue!\n");
        exit(0);
    }
    else
    {
        q->size--;
        q->front = succ( q->front, q );
    }
}

int
front( queue q )
{

    if( is_empty( q ) )
    {
        printf("empty queue!\n");
        exit(0);
    }
    else
        return q->array[q->front];
}

int
front_and_dequeue( queue q )
{
    int tmp;

    if( is_empty( q ) )
    {
        printf("empty queue!\n");
        exit(0);
    }
    else
    {
        tmp = q->array[q->front];
        q->size--;
        q->front = succ( q->front, q );
        return tmp;
    }

}

void
dispose_queue( queue q )
{
    if( q != NULL )
    {
        free(q->array);
        free(q);
    }
}

/* queue_test.c */

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

int
main(void)
{
    queue q;
    int tmp;
    int i;

    q = create_queue(10);
    printf("1 enqueue\n");
    enqueue(1, q);
    printf("2 enqueue\n");
    enqueue(2, q);
    printf("3 enqueue\n");
    enqueue(3, q);
    printf("4 enqueue\n");
    enqueue(4, q);
    printf("5 enqueue\n");
    enqueue(5, q);

    printf("\n");
    for(i=0; i<5; i++)
    {
        printf("dequeue %d\n", front_and_dequeue( q ));

    }

}

测试结果：