C++Primer Plus 第12章 类和动态内存分配001 12.10编程练习第5题new,delete的指向深度拷贝

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5. Heather 银行进行的研究表明，ATM 客户不希望排队时间不超过1分钟。使用程序清单 12.10中的模拟，找出要使平均等候时间为1分钟，每小时到达的客户数应为多少(试验时间不短于100小时)?

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前言

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Heather 银行进行的研究表明，ATM 客户不希望排队时间不超过1分钟。使用程序清单 12.10中的模拟，找出要使平均等候时间为1分钟，每小时到达的客户数应为多少(试验时间不短于100小时)?

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一、序求

修改程序清单12.10中模拟的程序。

二、程序清单引入

1.头文件

代码如下（示例）：

// queue.h -- interface for a queue
#ifndef QUEUE_H_
#define QUEUE_H_
// This queue will contain Customer items
class Customer
{
private:
    long arrive;        // arrival time for customer
    int processtime;    // processing time for customer
public:
    Customer() : arrive(0), processtime (0){}
    void set(long when);
    long when() const { return arrive; }
    int ptime() const { return processtime; }
};

typedef Customer Item;

class Queue
{
private:
// class scope definitions
    // Node is a nested structure definition local to this class
    struct Node { Item item; struct Node * next;};
    enum {Q_SIZE = 10};
// private class members
    Node * front;       // pointer to front of Queue
    Node * rear;        // pointer to rear of Queue
    int items;          // current number of items in Queue
    const int qsize;    // maximum number of items in Queue
    // preemptive definitions to prevent public copying
    Queue(const Queue & q) : qsize(0) { }
    Queue & operator=(const Queue & q) { return *this;}
public:
    Queue(int qs = Q_SIZE); // create queue with a qs limit
    ~Queue();
    bool isempty() const;
    bool isfull() const;
    int queuecount() const;
    bool enqueue(const Item &item); // add item to end
    bool dequeue(Item &item);       // remove item from front
};
#endif

2.读入数据

代码如下（示例）：

// queue.cpp -- Queue and Customer methods
#include "queue.h"
#include <cstdlib>         // (or stdlib.h) for rand()

// Queue methods
Queue::Queue(int qs) : qsize(qs)
{
    front = rear = NULL;    // or nullptr
    items = 0;
}

Queue::~Queue()
{
    Node * temp;
    while (front != NULL)   // while queue is not yet empty
    {
        temp = front;       // save address of front item
        front = front->next;// reset pointer to next item
        delete temp;        // delete former front
    }
}

bool Queue::isempty() const
{
    return items == 0;
}

bool Queue::isfull() const
{
    return items == qsize;
}

int Queue::queuecount() const
{
    return items;
}

// Add item to queue
bool Queue::enqueue(const Item & item)
{
    if (isfull())
        return false;
    Node * add = new Node;  // create node
// on failure, new throws std::bad_alloc exception
    add->item = item;       // set node pointers
    add->next = NULL;       // or nullptr;
    items++;
    if (front == NULL)      // if queue is empty,
        front = add;        // place item at front
    else
        rear->next = add;   // else place at rear
    rear = add;             // have rear point to new node
    return true;
}

// Place front item into item variable and remove from queue
bool Queue::dequeue(Item & item)
{
    if (front == NULL)
        return false;
    item = front->item;     // set item to first item in queue
    items--;
    Node * temp = front;    // save location of first item
    front = front->next;    // reset front to next item
    delete temp;            // delete former first item
    if (items == 0)
        rear = NULL;
    return true;
}

// customer method

// when is the time at which the customer arrives
// the arrival time is set to when and the processing
// time set to a random value in the range 1 - 3
void Customer::set(long when)
{
    processtime = std::rand() % 3 + 1;
    arrive = when; 
}

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