C++ 12 类

类定义

#pragma once

#include <string>

using namespace std;

class Screen {
	// 设置位友元
	friend class Window_Mgr;

public:
	// 默认构造函数
	Screen() : contents("hello class"), cursor(0), width(5) {}
	// 构造函数，默认实参 只能放在后面
	// explicit 抑制构造函数定义的隐式转换
	explicit	Screen(string text, int cur = 0, int w = 5) : contents(text), cursor(cur), width(w) {}

	typedef std::string::size_type index;
	char get() const { return contents[cursor]; }
	// 重载成员函数
	inline	char get(index x, index y) const;
	// 显示指定内联函数
	index get_cursor() const;

	Screen& move(index row, index offset); // 将光标移动到某行某位

	Screen& set(char); // 对光标指向位置赋值

	Screen& display(std::ostream &os) { do_display(os); return *this; }
	// 基于const的重载
	const	Screen& display(std::ostream &os) const { do_display(os); return *this; }

private:
	string contents;
	index cursor;
	index width;
	void do_display(std::ostream &os)const
	{
		os << contents << endl;
	}
};

inline char Screen::get(index x, index y) const
{
	index row = x * width;
	return contents[row + y];
}

inline Screen::index Screen::get_cursor() const
{
	return cursor;
}

类实现

#include "Screen.h"

Screen & Screen::move(index row, index offset)
{
	index skip = row * width;
	cursor = skip + offset;
	// this 指针的使用
	return *this;
}

Screen & Screen::set(char c)
{
	contents[cursor] = c;
	return *this;
}

类使用

#include <iostream>
#include <sstream>
#include "Screen.h"
#include "Account.h"

using namespace std;

void display(Screen screen);

int main()
{
	Screen screen;
	cout << "get() = " << screen.get() << endl;
	cout << "get(row,offset) = " << screen.get(0, 1) << endl;
	screen.move(0, 4).set('a');
	cout << "get() = " << screen.get() << endl;

	Screen myscreen("hello xiaohui");
	myscreen.set('*').display(std::cout);

	const Screen const_screen;
	const_screen.display(std::cout);

	string content = "good morning";
	// display(content); // 隐式转换为 Screen对象 explicit 抑制构造函数定义的隐式转换
	display(Screen(content)); // 显式转换

	Account ac1;
	double rate = 	ac1.rate();
	rate = Account::rate();

	return 0; 
}

void display(Screen screen)
{
	screen.display(cout);
}

友元

#pragma once
#include "Screen.h";
class Window_Mgr {
public:
	Window_Mgr&	relocate(Screen::index wid, Screen& s) {
		// Window_Mgr 为 Screen友元 ，可访问私有变量
		s.width += wid;
		return *this;
	}
};

静态变量

#pragma once
#include <string>
using namespace std;
class Account {
public:
	// 类成员直接使用静态变量
	void applyint() { amount += amount * interestRate; }
	// 静态函数没有this指针，不能引用成员变量
	static double rate() { return interestRate; }
	static void rate(double);
private:
	std::string owner;
	double amount;
	static double interestRate; // 静态变量 Account类型全体对象共享
	static double initRate();
};