c++两种设计模式 单例和工厂模式

一.单例

1.单例的概念

1.当前的类最多只能创建一个实例

2.当前这个唯一的实例，必须由当前类创建（自主创建），而不是调用者创建

3.必须向整个系统提供全局的访问点，来获取唯一的实例

2.单例的代码

#include <iostream>
using namespace std;class CSingleton {CSingleton(){}CSingleton(const CSingleton&) = delete;//弃用拷贝构造函数static CSingleton* m_spring;~CSingleton() {}
public:static struct DeleteSingleton {//保证申请的堆空间一定被回收~DeleteSingleton() {if(m_spring)delete m_spring;m_spring = nullptr;}} del;//静态对象，在程序结束时静态对象会自动被回收，然后就会调用析构函数，就一定能保证申请的堆空间被回收//有问题的代码，在多线程下，可能会创建多个对象static CSingleton* CreatCSingleton() {//加锁if (!m_spring) {//如果指针为空，则创建对象m_spring = new  CSingleton;}//解锁return m_spring;}static void DestoryCSingleton(CSingleton*& psin) {if (m_spring)delete m_spring;m_spring = nullptr;psin = nullptr;}/*~CSingleton() {//这里不能使用析构进行回收，这里回收的是对象，这样的话就会不断的调用析构if (m_spring) {delete m_spring;m_spring = nullptr;}}*/};
CSingleton::DeleteSingleton CSingleton::del;//类外定义初始化, 格式： 类型 类名::静态变量名
CSingleton* CSingleton:: m_spring(nullptr);int main() {//主函数进行测试CSingleton* p1 = CSingleton::CreatCSingleton();CSingleton* p2 = CSingleton::CreatCSingleton();cout << p1 << "   " << p2 << endl;CSingleton::DestoryCSingleton(p1);return 0;
}

3.懒汉式和饿汉式

懒汉式：当第一次调用这个接口函数时，先创建单例 时间换空间的做法

饿汉式：无论是否调用获取单例接口函数，都会提前创建单例 空间换时间的做法

懒汉式代码就是上面的代码

饿汉式代码

//饿汉式
class CSingleton {CSingleton() {}CSingleton(const CSingleton&) = delete;static CSingleton sing;~CSingleton() {}
public:static CSingleton* CreatCSingleton() {return &sing;}
};CSingleton CSingleton::sing; 

4.单例模式的优点

1.单例模式提供了严格的对唯一实例的创建，访问和销毁，安全性高

2.单例模式的实现可以节省系统资源

二.工厂模式

1.概念

工厂模式主要用来集中创建对象的，如果在任何使用的地方创建对象那就造成了类或方法之间的耦合，如果要更换对象那么在所有使用到的地方都要修改一遍，不利于后期的维护，也违背了开闭设计原则，如果使用工厂来创建对象，那么就彻底解耦合了，如果要修改著需要修改工厂类即可，工厂模式最大的优势：解耦

2.简单工厂

class CEngine {
public:virtual void woring() = 0;
};class  CEngine2L: public CEngine {void woring() {cout<<"2.0自然吸气发动机正在工作" <<endl;}
};class CEngine2T : public CEngine {void woring() {cout<<"2.0涡轮增压发动机正在工作" << endl;}class CCar {
public:CEngine* m_engine;CCar():m_engine(new CEngine2L){}CCar(const string&type) :m_engine(type=="2.0L"?(CEngine*)new CEngine2L: (CEngine*)new CEngine2T) {}//这里发生了耦合void dirve() {if (m_engine) {m_engine->woring();cout << "汽车正在行驶" << endl;}}~CCar() {if (m_engine) {delete m_engine;m_engine = nullptr;}}
};
int main() {CCar tst1;CCar tst2("2.0L");tst1.dirve();tst2.dirve();
}

简单工厂就是在上面代码的基础上进行解耦

耦合这里来看就是：如果发动机函数增加参数的话，那么汽车类中与发动机函数有交互的函数的内容也需要改，就是牵一发而动全身

进行解耦代码为

class CEngine {
public:virtual void woring() = 0;
};class  CEngine2L : public CEngine {void woring() {cout << "2.0自然吸气发动机正在工作" << endl;}
};class CEngine2T : public CEngine {void woring() {cout << "2.0涡轮增压发动机正在工作" << endl;}
};
//创建发动机的具体代码写在这里
class CFactoryEngine {
public:CEngine* CreatEngine(const string& type) {if (type == "2.0L") {return new CEngine2L;}else if (type == "2.0T") {return new CEngine2T;}else {return nullptr;}}
};class CCar {
public:CEngine* m_engine;CCar() :m_engine(new CEngine2L) {}//引入简单工厂后的写法CCar(CFactoryEngine* pFac,const string& type):m_engine(pFac? pFac->CreatEngine(type):nullptr){}void dirve() {if (m_engine) {m_engine->woring();cout << "汽车正在行驶" << endl;}}~CCar() {if (m_engine) {delete m_engine;m_engine = nullptr;}}
};
int main(){CFactoryEngine Fac;CCar audi(&Fac, "2.0L");audi.dirve();CCar benzi(&Fac, "2.0L"); benzi.dirve();
}

3.工厂方法

工厂方法就是在简单工厂的基础上 把工厂进行细化 每个产品对应一个工厂（之前的简单工厂每有一个新产品就要将工厂的功能进行修改很麻烦，工厂进行细化之后，如果有新的产品我们只需要增加工厂的功能就行了）

代码如下

#include <iostream>
using namespace std;class CEngine {
public:virtual void woring() = 0;
};class  CEngine2L : public CEngine {void woring() {cout << "2.0自然吸气发动机正在工作" << endl;}
};class CEngine2T : public CEngine {void woring() {cout << "2.0涡轮增压发动机正在工作" << endl;}
};class CFactoryEngine {
public:virtual CEngine* CreatEngine() = 0;
};class CFactoryEngine2L :public CFactoryEngine {
public:virtual CEngine* CreatEngine() {return new CEngine2L;}};class CFactoryEngine2T :public CFactoryEngine {
public:virtual CEngine* CreatEngine() {return new CEngine2T;}};class CCar {
public:CEngine* m_engine;CCar() :m_engine(new CEngine2L) {}CCar(CFactoryEngine* pFac) :m_engine(pFac ? pFac->CreatEngine() : nullptr) {}void dirve() {if (m_engine) {m_engine->woring();cout << "汽车正在行驶" << endl;}}~CCar() {if (m_engine) {delete m_engine;m_engine = nullptr;}}
};int main() {CFactoryEngine* Fac2L = new CFactoryEngine2L;CFactoryEngine* Fac2T = new CFactoryEngine2T;CCar audi(Fac2L);audi.dirve();CCar benzi(Fac2T);benzi.dirve();return 0;
}

4.抽象工厂

抽象工厂就是在工厂方法的基础上将所有工厂统一管理

代码如下

#include <iostream>
using namespace std;class CEngine {
public:virtual void woring() = 0;
};class  CEngine2L : public CEngine {void woring() {cout << "2.0自然吸气发动机正在工作" << endl;}
};class CEngine2T : public CEngine {void woring() {cout << "2.0涡轮增压发动机正在工作" << endl;}
};class CGearBox {
public:virtual void woring() = 0;
};class  CGearBoxAuto : public CGearBox {void woring() {cout << "自动变速器正在工作" << endl;}
};class CGearBoxMaual : public CGearBox {void woring() {cout << "手动变速器正在工作" << endl;}
};
//加速器
class CFactoryEngine {
public:virtual CEngine* CreatEngine() = 0;
};class CFactoryEngine2L :public CFactoryEngine {
public:virtual CEngine* CreatEngine() {return new CEngine2L;}};class CFactoryEngine2T :public CFactoryEngine {
public:virtual CEngine* CreatEngine() {return new CEngine2T;}};//变速器
class CFactoryEngineGearBox {
public:virtual CGearBox* CreatBox() = 0;
};class CFactoryEngineGearBoxAuto :public CFactoryEngineGearBox {
public:virtual CGearBox* CreatBox() {return new CGearBoxAuto;}};class CFactoryEngineGearBoxMaual :public CFactoryEngineGearBox {
public:virtual CGearBox* CreatBox() {return new CGearBoxMaual;}};//统一工厂
class CFactory {
public:virtual CGearBox* CreatBox() = 0;virtual void woring() = 0;
};class CFactory2TAuto :public CFactory {
public:virtual CGearBox* CreatBox() {return new CGearBoxAuto;}virtual CEngine* CreatEngine() {return new CEngine2T;}
};class CFactory2TMaual :public CFactory {
public:virtual CGearBox* CreatBox() {return new CGearBoxMaual;}virtual CEngine* CreatEngine() {return new CEngine2T;}
};
class CCar {
public:CEngine* m_engine;CGearBox* m_gearbox;CCar() :m_engine(new CEngine2L) {}CCar(CFactoryEngine* pFacEngine, CFactoryEngineGearBox* pFacGearBox) :m_engine(pFacEngine ? pFacEngine->CreatEngine() : nullptr), m_gearbox(pFacGearBox ? pFacGearBox->CreatBox() : nullptr){}void dirve() {if (m_engine) {m_engine->woring();cout << "汽车正在行驶" << endl;}if (m_gearbox) {m_gearbox->woring();cout << "变速器正在工作" << endl;}}~CCar() {if (m_engine) {delete m_engine;m_engine = nullptr;}if (m_gearbox) {delete m_gearbox;m_gearbox = nullptr;}}
};int main() {CFactoryEngine* PFa1 = new CFactoryEngine2L;CFactoryEngineGearBox* PFa2 = new CFactoryEngineGearBoxAuto;CCar audi(PFa1,PFa2);audi.dirve();return 0;
}