《C++PrimePlus》第10章 对象和类

10.1 过程性编程和面向对象编程

10.2 抽象和类

10.3 类的构造函数和析构函数

类的定义和使用（买卖股票）

头文件stock10.h

#ifndef  __STOCK00__H__
#define __STOCK00__H__#include <string>class Stock {
// pravate的内容只能通过public访问
private:std::string company; // 公司名字long shares; // 股票的数量double share_val; // 每只股票的价格double total_val; // 股票总价值void set_total() {total_val = shares * share_val;}; // 函数在类的声明中定义，将自动成为内联函数public:// 默认构造函数Stock();// 构造函数Stock(const std::string &co, long n = 0, double pr = 0.0);// 析构函数~Stock();// 买入股票：买入数量，买入价格void buy(long num, double price);// 卖出股票：卖出数量，卖出价格void sell(long num, double price);// 传递最新价格void update(double price);// 显示股票信息void show() const;
}; #endif // ! __STOCK00_H__

源代码usestock2.cpp

#include <iostream>
#include "stock10.h"int main() {using std::cout;cout << "Using constructors to create new objects\n";Stock stock1("NanoSmart", 12, 20.0); // 隐式调用stock1.show();Stock stock2 = Stock("Boffo Objects", 2, 2.0); // 显式调用stock2.show();cout << "Assigning stock1 to stock2:\n";stock2 = stock1; // 类的对象可以相互之间对拷cout << "Listing stock1 and stock2:\n";stock1.show();stock2.show();cout << "Using a constuctor to reset an Object\n";stock1 = Stock("Nifty Foods", 10, 50.0); // 创建临时变量再赋值cout << "Revised stock1:\n";stock1.show();cout << "Done\n";const Stock land = Stock{ "Klu Pro" };// show()函数要接收const的对象，函数定义时要在函数名后面加上constland.show();return 0;
}

源代码stock10.cpp

#include <iostream>
#include "stock10.h"Stock::Stock() {std::cout << "Default constructor called\n";company = "no name";shares = 0;share_val = 0.0;total_val = 0.0;
}Stock::Stock(const std::string &co, long n, double pr) {company = co;if (n < 0) {std::cout << "Number can't be negative, shares set to 0" << std::endl;shares = 0;}else shares = n;share_val = pr;set_total();
}Stock::~Stock() {std::cout << "Bye, " << company << "!\n";
}void Stock::buy(long num, double price) {if (num < 0) {std::cout << "Number can't be negative, transatcion failed." << std::endl;}else {shares += num;share_val = price;set_total();}
}void Stock::sell(long num, double price){if (num < 0) {std::cout << "Number can't be negative, transatcion failed." << std::endl;}else if (num > shares){std::cout << "Number is more than you have, transaction failed." << std::endl;}else {shares -= num;share_val = price;set_total();}
}void Stock::update(double price) {share_val = price;set_total();
}void Stock::show() const{ // 代表函数不会修改值，可以接收const的对象std::cout << "Company: " << company << std::endl;std::cout << "Shares: " << shares << std::endl;std::cout << "Share price: " << share_val << std::endl;std::cout << "Total worth: " << total_val << std::endl;
}

10.4 This指针

This指针的使用（比较股票总值）

// 比较股票的总金额，并返回一个对象
// 第2个const：函数不会修改被显式访问的对象
// 第3个const：函数不会修改被隐式访问的对象
// 第1个const：函数会返回一个const Stock对象
const Stock & Stock::topval(const Stock & s) const{if (s.total_val > total_val) // total_val == this->total_valreturn s;elsereturn *this; // this是一个指针，要返回值需要取值运算符
}

10.5 对象数组

使用对象数组（找出总价值最大的股票）

int main(){Stock stocks[4] = {Stock("NanoSmart", 12, 20.0),Stock("Boffo Objects", 200, 2.0),Stock("Monolithic Obelisks", 130, 3.25),Stock("Fleep Enterprises", 60, 6.5)};std::cout << "Stock holdings:\n";int st;for (st = 0; st < 4; st++)stocks[st].show();const Stock * top = &stocks[0];for (st = 1; st < 4; st++)// 使用指针的方法返回一个对象，然后再取地址赋给toptop = &top->topval(stocks[st]);std::cout << "\nMost valuable holding:\n";top->show();return 0;
}

10.6 类作用域

10.7 抽象数据类型

使用类实现抽象数据类型（栈）

头文件stack.h

#ifndef  __STACK__H__
#define __STACK__H__typedef unsigned long Item; // 类型别名，如果需要放别的类型就改这里class Stack {private:enum {MAX = 10}; // 创建枚举类型，遇到MAX就替换成10Item items[MAX];int top; // 栈顶的指针public:Stack();bool isempty() const; // 栈是否为空bool isfull() const; // 栈是否满了bool push(Item &item); // 入栈，成功返回1，失败返回0bool pop(Item &item); // 出栈，成功返回1，失败返回0
}; #endif

源文件stacker.cpp

#include <iostream>
#include "stack.h"
using namespace std;int main() {char ch;unsigned long po;Stack st;cout << "Enter 'A' to push to stack\n";cout << "Enter 'P' to pop from stack\n";cout << "Enter 'Q' to quit\n";while (cin >> ch && ch != 'Q') {while (cin.get() != '\n') // 删除输入行中剩余部分continue;switch (ch) {case 'A':cout << "Enter a number:" << endl;cin >> po;if (st.isfull())cout << "Stack already full." << endl;elsest.push(po);break;case 'P':if (st.isempty())cout << "Stack is empty." << endl;else {st.pop(po);cout << po << " is poped." << endl;}break;}cout << "Enter 'A' to push to stack\n";cout << "Enter 'P' to pop from stack\n";cout << "Enter 'Q' to quit\n";}return 0;
}

源文件stack.cpp

#include "stack.h"Stack::Stack() {top = 0;
}bool Stack::isempty() const {return top == 0;
}bool Stack::isfull() const {return top == MAX;
}bool Stack::push(Item &item){if (top < MAX) {items[top++] = item; // 先操作，后加加return true;}elsereturn false;
}bool Stack::pop(Item &item) {if (top > 0) {item = items[--top]; // 先减减，再操作return true;}elsereturn false;
}