C++ Primer Plus学习：第十二章 类和动态内存（3）

成员 初始化列表的句法

Class::Classy(int n,int m):mem1(n),mem2(0),mem3(n*m+2)
{
//.....
}

初始化成员列表

mem1:n

mem2:0

mem3:n*m+2

注意

此格式仅可用于构造函数

必须用此格式各初始化非静态const数据成员

必须用这种格式来初始化引用数据成员

eg

queue.h

#ifndef QUEUE_H_
#define QUEUE_H_

class Customer
{
private:
long arrive;
int processtime;
public:
Customer()
{
arrive = processtime = 0;
}
void set(long when);
long when()const
{
return arrive;
}
int ptime()const
{
return processtime;
}
};

typedef Customer Item;
class Queue
{
private:
struct Node{Item item;struct Node *next;};
enum{Q_SIZE = 10};
Node * front;
Node * rear;
int items;
const int qsize;
Queue(const Queue & q):qsize(0){}
Queue & operator=(const Queue & q){return *this;}
public:
Queue(int qs = Q_SIZE);
~Queue();
bool isempty()const;
bool isfull()const;
int queuecount()const;
bool enqueue(const Item & item);
bool dequeue(Item &item);
};
#endif

queue.cpp

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

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

Queue::~Queue()
{
Node * temp;
while(front!=NULL)
{
temp = front;
front = front->next;
delete temp;
}
}
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;
if(add == NULL)
return false;
add->item = item;
add->next = NULL;
items++;
if(front == NULL)
front = add;
else
rear->next = add;
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;
items--;
Node * temp = front;
front  = front->next;
delete temp;
if(items == 0)
rear = NULL;
return true;
}
void Customer::set(long when)
{
processtime = std::rand()%3+1;
arrive = when;
}

bank.cpp

#include <iostream>
#include <cstdlib>
#include <ctime>
#include "queue.h"

const int MIN_PER_HR = 60;
bool newcustomer(double x);

int main()
{
using std::cin;
using std::cout;
using std::endl;
using std::ios_base;
std::srand(std::time(0));

cout<<"Case Study:Bank of Heather Automatic Teller\n";
cout<<"Enter maximum size of queue: ";
int qs;
cin>>qs;
Queue line(qs);

cout<<"Enter the number of simulation hours: ";
int hours;
cin>>hours;
long cyclelimit = MIN_PER_HR*hours;
cout<<"Enter the average number of customers per hour: ";
double perhour;
cin>>perhour;
double min_per_cust;
min_per_cust = MIN_PER_HR;

Item temp;
long trunaways = 0;
long customers = 0;
long served = 0;
long sum_line = 0;
int wait_time = 0;
long line_wait = 0;

for(int cycle = 0;cycle<cyclelimit;cycle++)
{
if(newcustomer(min_per_cust))
{
if(line.isfull())
trunaways++;
else
{
customers++;
temp.set(cycle);
line.enqueue(temp);
}
}
if(wait_time<=0 && line.isempty())
{
line.dequeue(temp);
wait_time = temp.ptime();
line_wait += cycle-temp.when();
served++;
}
if(wait_time>0)
wait_time--;
sum_line +=line.queuecount();
}

if(customers>0)
{
cout<<"customers accepted: "<<customers<<endl;
cout<<" customers served: "<<served<<endl;
cout<<"           trunaways: "<<trunaways<<endl;
cout<<"average queue size: ";
cout.precision(2);
cout.setf(ios_base::fixed,ios_base::floatfield);
cout.setf(ios_base::showpoint);
cout<<(double)sum_line/cyclelimit<<endl;
cout<<" average wait time: "<<(double)line_wait/served<<" minutes\n";
}
else
cout<<"No customers!\n";
cout<<"Done!\n";

system("pause");
return 0;
}

bool newcustomer(double x)
{
return (std::rand()*x/RAND_MAX<1);
}