[C++知识库]简单工厂模式

简单工厂模式

利用简单工厂模式，实现两个数的运算，返回运算结果。

1. uml类图

2. C++程序实现

#include <iostream>
#include <memory>
#include <string>

//  运算类
class Calculator
{
public:
    double first_number = 0.0;
    double second_number = 0.0;
    enum operator_type
    {
        add = '+',
        sub = '-',
        mul = '*',
        dev = '/'
    };

public:
    virtual std::string getResult(){};
};

// 加法类
class AddOperator : public Calculator
{
public:
    std::string getResult() override
    {
        return std::to_string(first_number + second_number);
    }
};

// 减法类
class SubOperator : public Calculator
{
public:
    std::string getResult() override
    {
        return std::to_string(first_number - second_number);
    }
};

// 乘法类
class MulOperator : public Calculator
{
public:
    std::string getResult() override
    {
        return std::to_string(first_number * second_number);
    }
};

// 除法类
class DivOperator : public Calculator
{
public:
    std::string getResult() override
    {
        if (second_number == 0)
            return "Error: divisor cannot be zero";
        return std::to_string(first_number / second_number);
    }
};

// 运算的工厂类
class CalculatorFactory
{
public:
    std::shared_ptr<Calculator> creat_operator(Calculator::operator_type type)
    {
        switch (type)
        {
        case Calculator::operator_type::add:
            return std::make_shared<AddOperator>();
            break;
        case Calculator::operator_type::sub:
            return std::make_shared<SubOperator>();
            break;
        case Calculator::operator_type::mul:
            return std::make_shared<MulOperator>();
            break;
        case Calculator::operator_type::dev:
            return std::make_shared<DivOperator>();
            break;

        default:
            break;
        }
    }
};

int main()
{
    char a;
    double b(0), c(0);
    // 依次输入 第一个数  运算符  第二个数
    std::cin >> b >> a >> c;

    // 采用工厂类，建立对应的子类，输出运算结果
    CalculatorFactory factor;
    auto oper = factor.creat_operator(Calculator::operator_type(a));
    oper->first_number = b;
    oper->second_number = c;
    std::cout << b << a << c << "=" << oper->getResult() << std::endl;
}

本文参考：<<大话设计模式>>