C++ 数据共享与保护学习记录【代码】
一.项目一
1.头文件.h
//A.h
#pragma once
//防止头文件被重复包含（重复包含会被重复编译，也就是该类会被重复定义）
#ifndef HEAD_H
//等价于（ #if !defined(HEAD_H) )
//defined是一个预处理操作符，相当于一个表达式
#define HEAD_H
class A
{
public:static void f(A a);static void show();//构造函数//只能在初始化列表初始化常数据成员A(int x, int conx) :x(x), conx(conx) { x2++; }
private:int x;static int x2;const int conx;
};
//必须有结束指令
#endif
//Clock.h
#pragma once
#include<string>
using namespace std;
class Clock
{
public:Clock();void setTime(int newH, int newM, int newS, string newN);void showTime() const;//友元类friend class Point;
private:int hour, minute, second;string name;//类的静态常量如果有整数类型或枚举类型，可以在定义中指定常量值（不分配内存，只是简单替换）static const int b = 10;
};
//内联函数不用分配内存（定义在头文件中）
inline int add(int a, int b) {return a + b;
}
//Point.h
#pragma once
#include"Clock.h"
class Point
{
public:Point(int x = 0, int y = 0) :x(x), y(y) {}int getX() const{ return x; }int getY() const{ return y; }//友元函数friend float dist(Point& p1, Point& p2);//作为Clock的友元类，可以访问其私有成员void show_Clock(Clock& c);
private:int x, y;
};2.源文件.cpp
//A.cpp
#include "A.h"
#include<iostream>
using namespace std;//外部变量只能放在.cpp下，不能在.h下（定义型声明）（文件作用域）
extern int j = 20;//外部函数（不声明，文件作用域）
void showing(){cout << "Hello Extern Function!--NOT--DEFINE" << endl;
}
//外部函数（声明为全局）
extern void showed() {cout << "Hello Extern Function!--DEFINE" << endl;
}
//静态函数（不能被其他编译单元引用）（静态生存期）
void static shows() {cout << "Hello Static Function!" << endl;
}//必须在类外使用类名进行定义式声明（初始化）
int A::x2 = 0;void A::f(A a) {// cout << x; //不能在静态成员函数中直接访问非静态成员，必须与特定成员相对cout << "a.x:" << a.x << endl;cout << "x2:" << x2 << endl; // 可以直接访问静态成员}void A::show() {cout << "x2:" << x2 << endl;
}//Clock.cpp
#include "Clock.h"
#include<iostream>
#include<string>
using namespace std;
//文件作用域（没有声明，但是在main函数中引用性声明，值也相同）
int i = 10;
Clock::Clock() :hour(0), minute(0), second(0) {cout << "调用构造函数" << endl;
}void Clock::setTime(int newH, int newM, int newS, string newN) {name = newN;hour = newH;minute = newM;second = newS;
}
void Clock::showTime() const {cout << hour << ":" << minute << ":" << second << endl;cout << name << endl;
}//Point.cpp
#include "Point.h"
#include<iostream>
#include<cmath>
using namespace std;
//友元函数实现
float dist(Point& p1, Point& p2) {double x = p1.x - p2.x;double y = p1.y - p2.y;//static_cast是一种类型转换运算符，用于在编译时进行类型转换return static_cast<float>(sqrt(x * x + y * y));
}void Point::show_Clock(Clock& c) {cout << "This is showed by Point" << this->x << " " << this->y << endl;cout << c.name << endl;
}3.主函数.cpp
//main.cpp
#include"Clock.h"
#include"A.h"
#include"Point.h"
#include<iostream>
#include<string>
using namespace std;
// 定义未指定初值的基本类型静态生存期变量，会被以0值初始化
// 声明具有静态生存期的对象
Clock globalClock;int main() {//生存期cout << "生存期" << endl;cout << "First:" << endl;globalClock.showTime();globalClock.setTime(8, 30, 30, "theclock");Clock myClock(globalClock);cout << "Second:" << endl;myClock.showTime();//静态成员 A a1(100,100);A a2(99,100);//调用静态成员函数cout << "调用静态成员函数" << endl;A::f(a1);A::f(a2);A::show();//友元函数cout << "友元函数" << endl;Point myp1(1, 1), myp2(4, 5);cout << "The distance is:" << endl;cout << dist(myp1, myp2);//友元类//友元关系：不可传递，单向，不被继承//友元函数不仅可以是普通的函数，也可以是另外一个类的成员函数cout << "通过友元类输出私有类成员：" << endl;myp1.show_Clock(myClock);//调用内联函数cout << "4 + 5 = " << add(4, 5) << endl;//外部变量extern定义（引用性声明）extern int i;cout << "外部变量 i = " << i << endl;//在源文件中声明后还要再声明，此时值一致extern int j;cout << "外部变量 j = " << j << endl;//外部函数(使用要包含文件+函数声明)void showing();//extern void showing();//也可showing();void showed();showed();//不能访问其他编译单元静态函数//void shows();//shows();return 0;
}4.输出
调用构造函数
生存期
First:
0:0:0Second:
8:30:30
theclock
调用静态成员函数
a.x:100
x2:2
a.x:99
x2:2
x2:2
友元函数
The distance is:
5通过友元类输出私有类成员：
This is showed by Point1 1
theclock
4 + 5 = 9
外部变量 i = 10
外部变量 j = 20
Hello Extern Function!--NOT--DEFINE
Hello Extern Function!--DEFINE二.个人银行账户管理系统
（主要添加静态数据成员static，常成员const，条件预编译，并且实现头文件源文件文件分离）
1.头文件.h
//account.h
#pragma once
//条件预编译指令
#ifndef __ACCOUNT_H__
#define __ACCOUNT_H__
class SavingsAccount
{
private:int id; //账号double balance; //余额double rate; //存款的年利率int lastDate; //上次变更余额的时期double accumulation; //余额按日累加之和static double total; //所有账户总余额//记录一笔账, date为日期, amount为金额, desc为说明void record(int date, double amount);//获得到指定日期为止的存款金额按日累积值double accumulate(int date) const {return accumulation + balance * (date - lastDate);}
public:SavingsAccount(int date, int id, double rate); //构造函数int getId() const { return id; }double getBalance() const { return balance; }double getRate() const { return rate; }static double getTotal() { return total; }void deposit(int date, double amount); //存入现金void withdraw(int date, double amount); //取出现金//结算利息，每年1月 1日调用一次该函数void settle(int date);//显示账户信息void show() const;//友元函数friend void show_items(SavingsAccount& s1);//友元类friend class AnotherAccount;
};
#endif//AnotherAccount.h
#pragma once
#include"account.h"
class AnotherAccount
{
//成员函数可以访问SavingsAccount的保护和私有成员
private:SavingsAccount S1;SavingsAccount S2;
public:AnotherAccount(SavingsAccount& s1,SavingsAccount& s2):S1(s1),S2(s2) {}void showing() const;
};2.源文件.cpp
//account.cpp
#include "account.h"
#include<iostream>
using namespace std;// 一定要在类外初始化静态本地变量，不然会报错
double SavingsAccount::total = 0;// 友元函数实现
void show_items(SavingsAccount& s1) {cout << "id:" << s1.id << " balance:" << s1.balance << " lastDate:" << s1.lastDate << endl;
}//SavingsAccount类相关成员函数的实现
SavingsAccount::SavingsAccount(int date, int id, double rate): id(id), balance(0), rate(rate), lastDate(date), accumulation(0) {cout << date << "\t#" << id << " is created" << endl;
}
void SavingsAccount::record(int date, double amount) {accumulation = accumulate(date);lastDate = date;amount = floor(amount * 100 + 0.5) / 100; //保留小数点后两位（四舍五入）balance += amount;total += amount;cout << date << "\t#" << id << "\t" << amount << "\t" << balance << endl;
}
void SavingsAccount::deposit(int date, double amount) {record(date, amount);
}
void SavingsAccount::withdraw(int date, double amount) {if (amount > getBalance())cout << "Error: not enough money" << endl;elserecord(date, -amount);
}
void SavingsAccount::settle(int date) {double interest = accumulate(date) * rate / 365; //计算年息if (interest != 0)record(date, interest);accumulation = 0;
}
void SavingsAccount::show() const{cout << "#" << id << "\tBalance: " << balance;
}//AnotherAccount.cpp
#include "AnotherAccount.h"
#include<iostream>
using namespace std;
//访问SavingsAccount的私有成员
void AnotherAccount::showing() const{if (S1.balance > S2.balance) {cout << "The bigger is:" << S1.id << " balance:" << S1.balance << endl;}else if (S1.balance < S2.balance) {cout<< "The bigger is:" << S2.id << " balance:" << S2.balance << endl;}else {cout << "No one bigger than the other" << endl;}
}3.主函数.cpp
//5-11.cpp
#include<iostream>
#include"account.h"
#include"AnotherAccount.h"
using namespace std;int main() {//建立几个账户cout << "建立账户：" << endl;SavingsAccount sa0(1, 1234567, 0.02);SavingsAccount sa1(5, 7654321, 0.025);//几笔账目cout << "记账：" << endl;sa0.deposit(5, 670000);sa1.deposit(6, 700000);sa0.deposit(60, 5500);sa1.withdraw(70, 4000);//开户后第100天到了银行的计息日，结算所有账户的年息cout << "结息：" << endl;sa0.settle(100);sa1.settle(100);//输出各个账户信息cout << "输出各个账户信息：" << endl;sa0.show();cout << endl;sa1.show();cout << endl;cout << "利用静态本地变量const唯一初始化性输出total：" << endl;cout << "Total:" << SavingsAccount::getTotal() << endl;//利用友元函数输出账户信息cout << "利用友元函数输出账户信息:" << endl;show_items(sa0);show_items(sa1);//友元类cout << "友元类访问私有成员然后输出：" << endl;AnotherAccount s1(sa0,sa1);s1.showing();return 0;
}4.输出
建立账户：
1 #1234567 is created
5 #7654321 is created
记账：
5 #1234567 670000 670000
6 #7654321 700000 700000
60 #1234567 5500 675500
70 #7654321 -4000 696000
结息：
100 #1234567 3499.73 679000
100 #7654321 4498.63 700499
输出各个账户信息：
#1234567 Balance: 679000
#7654321 Balance: 700499
利用静态本地变量const唯一初始化性输出total：
Total:1.3795e+06
利用友元函数输出账户信息:
id:1234567 balance:679000 lastDate:100
id:7654321 balance:700499 lastDate:100
友元类访问私有成员然后输出：
The bigger is:7654321 balance:700499三.其他
1.限定作用域的enum枚举类
//限定作用域的enum枚举类
#include<iostream>
#include<string>
using namespace std;
enum color { red, yellow, green };
//enum color1 { red, yellow, green }; //错误，枚举类型不能重复定义
enum class color2 { red, yellow, green }; // 正确 限定作用域的枚举元素被隐藏
color c = red;
//color2 c1 = red; // color类型的值不能用来初始化color2类型实体
color c2 = color::red; // 显式的访问枚举元素
color2 c3 = color2::red; // 使用color2枚举元素
struct SColor {enum color { red, yellow, green };
};
SColor::color c = SColor::red; // 正确使用未限定作用域的枚举元素
2.常成员函数举例
//常成员函数举例
#include<iostream>
using namespace std;class R {
public:R(int r1, int r2) :r1(r1), r2(r2) {}void print();void print() const;
private:int r1, r2;
};void R::print() {cout << r1 << "---" << r2 << endl;
}void R::print() const {cout << r1 << "+++" << r2 << endl;
}int main() {R a(5, 4);a.print(); //调用普通函数成员const R b(20, 25);b.print(); //调用常函数成员return 0;
}//输出
5---4
20+++25