工厂方法模式(大话设计模式)C/C++版本

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工厂方法模式

C++

参考：https://www.cnblogs.com/Galesaur-wcy/p/15926711.html

#include <iostream>
#include <memory>
using namespace std;// 运算类
class Operation
{
private:double _NumA;double _NumB;public:void SetNumA(){cout << "Enter a double number: ";if (!(cin >> _NumA))throw "It must be a number";}double GetNumA(){return _NumA;}void SetNumB(){cout << "Enter a double number: ";if (!(cin >> _NumB))throw "It must be a number";}double GetNumB(){return _NumB;}virtual double GetResult(){int result = 0;return result;}
};class OperationAdd : public Operation
{
public:double GetResult(){double result = GetNumA() + GetNumB();return result;}
};class OperationSub : public Operation
{
public:double GetResult(){double result = GetNumA() - GetNumB();return result;}
};class OperationMul : public Operation
{
public:double GetResult(){double result = GetNumA() * GetNumB();return result;}
};class OperationDiv : public Operation
{
public:double GetResult(){if (GetNumB() == 0){throw "The divisor cannot be 0";}double result = GetNumA() / GetNumB();return result;}
};class Factory
{
public:virtual Operation *CreatOperation() = 0;
};class AddFactory : public Factory
{
public:Operation *CreatOperation(){return new OperationAdd();}
};class SubFactory : public Factory
{
public:Operation *CreatOperation(){return new OperationSub();}
};class MulFactory : public Factory
{
public:Operation *CreatOperation(){return new OperationMul();}
};class DivFactory : public Factory
{
public:Operation *CreatOperation(){return new OperationDiv();}
};/* 封装一下用户选择工厂创建的过程（属于客户端代码） */
Factory * CreatFactory(char operator_type)
{switch (operator_type){case '+':return new AddFactory;break;case '-':return new SubFactory;break;case '*':return new MulFactory;break;case '/':return new DivFactory;break;default:throw "Error input operator!";break;}return nullptr;
}int main()
{cout << "Choose an operation:";char operator_char;cin >> operator_char;try{//unique_ptr<Factory> fac = unique_ptr<Factory>(CreatFactory(operator_char));//智能指针更安全Factory* fac = CreatFactory(operator_char);//unique_ptr<Operation> oper = unique_ptr<Operation>(fac->CreatOperation());Operation* oper = fac->CreatOperation();oper->SetNumA();oper->SetNumB();cout << "result is: " << oper->GetResult() << endl;}catch (const char *err){cerr << err << endl;return -1;}return 0;
}

C

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>typedef struct Operation
{double NumA;double NumB;double (*GetResult)(struct Operation *);void (*SetNumA)(struct Operation *);void (*SetNumB)(struct Operation *);
} Operation;typedef struct OperationAdd
{Operation base; // 设置为第一个成员属性，模拟继承
} OperationAdd;typedef struct OperationSub
{Operation base;
} OperationSub;typedef struct OperationMul
{Operation base;
} OperationMul;typedef struct OperationDiv
{Operation base;
} OperationDiv;double OperationAddGetResult(struct Operation *op)
{OperationAdd *add = (OperationAdd *)op;return add->base.NumA + add->base.NumB;
}double OperationSubGetResult(struct Operation *op)
{OperationSub *sub = (OperationSub *)op;return sub->base.NumA - sub->base.NumB;
}double OperationMulGetResult(struct Operation *op)
{OperationMul *mul = (OperationMul *)op;return mul->base.NumA * mul->base.NumB;
}double OperationDivGetResult(struct Operation *op)
{OperationDiv *div = (OperationDiv *)op;if (div->base.NumB == 0){fputs("The divisor cannot be 0\n", stderr);exit(EXIT_FAILURE);}return div->base.NumA / div->base.NumB;
}typedef struct Factory
{Operation* (*CreatOperation)();
}Factory;typedef struct FactoryAdd
{Factory base;
} FactoryAdd;typedef struct FactorySub
{Factory base;
} FactorySub;typedef struct FactoryMul
{Factory base;
} FactoryMul;typedef struct FactoryDiv
{Factory base;
} FactoryDiv;void SetNumA(Operation *ope)
{printf("Enter a double number: ");if (scanf("%lf", &ope->NumA) != 1){fputs("It must be a number\n", stderr);exit(EXIT_FAILURE);}
}void SetNumB(Operation *ope)
{printf("Enter a double number: ");if (scanf("%lf", &ope->NumB) != 1){fputs("It must be a number\n", stderr);exit(EXIT_FAILURE);}
}Operation *CreatOperationAdd()
{Operation *op = malloc(sizeof(Operation));op->GetResult = OperationAddGetResult;op->SetNumA = SetNumA;op->SetNumB = SetNumB;return op;
}Operation *CreatOperationSub()
{Operation *op = malloc(sizeof(Operation));op->GetResult = OperationSubGetResult;op->SetNumA = SetNumA;op->SetNumB = SetNumB;return op;
}Operation *CreatOperationMul()
{Operation *op = malloc(sizeof(Operation));op->GetResult = OperationMulGetResult;op->SetNumA = SetNumA;op->SetNumB = SetNumB;return op;
}Operation *CreatOperationDiv()
{Operation *op = malloc(sizeof(Operation));op->GetResult = OperationDivGetResult;op->SetNumA = SetNumA;op->SetNumB = SetNumB;return op;
}Factory *CreateFactory(char op)
{Factory *fac = NULL;switch (op){case '+':fac = malloc(sizeof(FactoryAdd));fac->CreatOperation = CreatOperationAdd;break;case '-':fac = malloc(sizeof(FactorySub));fac->CreatOperation = CreatOperationSub;break;case '*':fac = malloc(sizeof(FactoryMul));fac->CreatOperation = CreatOperationMul;break;case '/':fac = malloc(sizeof(FactoryDiv));fac->CreatOperation = CreatOperationDiv;break;default:fputs("Error input operator!\n", stderr);return NULL;}return fac;
}int main()
{printf("Choose an operation: ");char operator_char = getchar();Factory* fac = CreateFactory(operator_char);Operation *oper = fac->CreatOperation();if (!oper)return EXIT_FAILURE;oper->SetNumA(oper);oper->SetNumB(oper);printf("Result is: %f\n", oper->GetResult(oper));free(oper);return 0;
}

对比简单工厂模式

简单工厂模式例子

1. 给四种运算新建了四个具体工厂类
2. 将简单工厂类模式中的工厂创建逻辑判断，移到了客户端代码中

工厂方法模式这样做的目的就是：对创建工厂类的修改关闭，对具体工厂类的扩展开放。

思维思路：

1. 简单工厂类中的创建工厂类中直接与具体的运算符号产生了依赖，不易于扩展(后期增加运算符，得直接修改工厂类)。
2. 为了降低耦合，根据依赖倒置的原则（细节依赖抽象），将创建工厂类的分支判断直接改成对应的具体工厂类。

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