单例模式实现案例

梦里梦外; 2022-05-15 01:29 251阅读 0赞

我们实现了一个电脑窗口类,众所周知,电脑窗口只有一个,不可以进行拷贝,复制,因此我们使用单例模式

#include <iostream>
    #include <limits>
    #include <cstdlib>
    using namespace std;
    
    class Screen {
    private:
    	unsigned int _width;
    	unsigned int _height;
    	
    	Screen(unsigned int width, unsigned int height) {
    		_width = width;
    		_height = height;
    	};
    	Screen() {    //不能通过常规手段生成对象
    
    	}
    	~Screen() {
    		delete instance;
    		instance = nullptr;
    	}
    public:
    	static Screen* instance;        //单例
    	Screen(const Screen&) = delete;       //同时不允许用拷贝的方式进行赋值
    	Screen& operator= (const Screen&) = delete; 
    
    	static Screen* getInstance() {
    		if (instance == nullptr) {
    			instance = new Screen();
    		}
    		return instance;
    	}
    
    	static Screen* getInstance(int theWidht, int theHeight){
    
    		if (instance == nullptr) {
    			instance = new Screen();
    		}
    
    		if ((theWidht > 0 && theWidht <= 1920) && (theHeight > 0 && theHeight <= 1080)) {
    			instance->_width = theWidht;
    			instance->_height = theHeight;
    		}
    		else {
    			instance->_width = 1920;
    			instance->_height = 1080;
    		}
    
    		return instance;
    	}
    	unsigned int getWidth() const{
    		return _width;
    	}
    	unsigned int getHeight() const{
    		return _height;
    	}
    };
    
    Screen* Screen::instance = nullptr;
    
    int main() {
    	int width, height;
    	Screen* screen = 0;
    	cin >> width >> height;
    	screen = Screen::getInstance(width, height); //进行初始化操作,初始化instance,只有这么一个实例
    	screen = Screen::getInstance();
    	cout << screen->getWidth() << " " <<
    		screen->getHeight() << endl;
    
    
    	system("PAUSE");
    	return 0;
    }