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使用工厂模式来生产某类对象（代码简化且容易维护，类之间有血缘关系，可以通过工厂类进行生产）；

简单工厂模式（用于创建简单对象）

对于简单工厂模式，需要的工厂类只有一个；

在工厂类中的公共成员函数来创建所需对象；

#include <bits/stdc++.h>
using namespace std;
// 产品父类 
class shape{
public:virtual void cal() = 0;virtual ~shape(){}
}; class triangle:public shape{
public:void cal() override{cout<<"三角形面积";}
};class square:public shape{
public:void cal() override{cout<<"正方形面积";}
};class cycle:public shape{
public:void cal() override{cout<<"圆形面积";}
};// 工厂类
enum class Type:char{triangle , square , cycle
};
class fac{
public:shape* creat_kinds(Type type){shape* ptr = nullptr;switch(type){case Type::triangle:ptr = new triangle;break;case Type::square:ptr = new square;break;case Type::cycle:ptr = new cycle;break;}return ptr;}
}; 
int main(){fac* cur = new fac;shape* obj = cur->creat_kinds(Type::cycle);obj->cal();return 0;
}

工厂模式

简单工厂模式会违反开放封闭原则 在添加类时需要修改子类、枚举类、工厂类、和判断代码

工厂模式通过创立N个工厂类来解决上述问题（对简单工厂模式解耦合），对已经写好的代码无需修改；

#include <bits/stdc++.h>
using namespace std;
// 产品父类 
class shape{
public:virtual void cal() = 0;virtual ~shape(){}
}; class triangle:public shape{
public:void cal() override{cout<<"三角形面积"<<endl;}
};class square:public shape{
public:void cal() override{cout<<"正方形面积"<<endl;}
};class cycle:public shape{
public:void cal() override{cout<<"圆形面积"<<endl;}
};// 工厂类
class fac{
public:virtual shape* creat_kinds() = 0;virtual ~fac(){}
}; class triangle_fac:public fac{
public:shape* creat_kinds(){return new triangle;}~triangle_fac(){cout<<"三角形被析构"; }
};
class square_fac:public fac{
public:shape* creat_kinds(){return new square;}~square_fac(){cout<<"三角形被析构"; }
};class cycle_fac:public fac{
public:shape* creat_kinds(){return new cycle;}~cycle_fac(){cout<<"三角形被析构"; }
};
int main(){fac* cur = new cycle_fac;shape* obj = cur->creat_kinds();obj->cal();delete obj;delete cur;return 0;
}

抽象工厂模式

通过造船，船分为三个模块，船体、武器、动力，三个模块又分为了简易、标准、旗舰三个版本

#include <bits/stdc++.h>
using namespace std;
// 三个抽象类 每个抽象类下三个具体派生类
// 抽象工厂类 一个抽象类 三个派生类
class body{
public:virtual void getbody() = 0;virtual ~body(){}
}; class wood_body:public body{
public:void getbody() override{cout<<"船的船体为<木头>---";}
};class iron_body:public body{
public:void getbody() override{cout<<"船的船体为<钢铁>---";}
};class mental_body:public body{
public:void getbody() override{cout<<"船的船体为<合成金属>---";}
};class weapon{
public:virtual void getweapon() = 0;virtual ~weapon(){} 
};class gun_weapon:public weapon{
public:void getweapon() override{cout<<"船的武器为<枪>---" ;}
};class cannon_weapon:public weapon{
public:void getweapon() override{cout<<"船的武器为<炮>---" ;}
};class laser_weapon:public weapon{
public:void getweapon() override{cout<<"船的武器为<激光>---" ;}
};class power{
public:virtual void getpower() = 0;virtual ~power(){} 
}; class human_power:public power{
public:void getpower() override{cout<<"船的动力为<手动>---"; }
};class engine_power:public power{
public:void getpower() override{cout<<"船的动力为<内燃机>---"; }
};class nuclear_power:public power{
public:void getpower() override{cout<<"船的动力为<核反应堆>---"; }
};class ship{
private:body* m_body;weapon* m_weapon;power* m_power;
public:ship(body* o_body , weapon* o_weapon , power* o_power):m_body(o_body) , m_weapon(o_weapon) , m_power(o_power){m_body->getbody();m_weapon->getweapon();m_power->getpower(); }~ ship(){delete m_body;delete m_weapon;delete m_power;} 
};class fac{
public:virtual ship* get() = 0;~ fac(){}
}; class e_fac:public fac{
public:ship* get() override{ship* cur = new ship(new wood_body , new gun_weapon , new human_power);return cur;}
};class m_fac:public fac{
public:ship* get() override{ship* cur = new ship(new iron_body , new cannon_weapon , new engine_power);return cur;}
};class h_fac:public fac{
public:ship* get() override{ship* cur = new ship(new mental_body , new laser_weapon , new nuclear_power);return cur;}
};int main() {fac* cur = new h_fac;ship* res = cur->get();delete cur;delete res;return 0;
}

描述：首先定义三个抽象类，代表船的三个组成部分（船体、武器、动力）;每个抽象类下有三个派生类，分别对应初级船、中级船、高级船所用的对应材料。通过ship类将船的三个部分组成起来，一个工厂抽象类fac，通过工厂抽象类的派生类，结合ship类设置三种规格的船。