Design Patterns----简单的工厂模式

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实例：

实现一个简单的计算器。实现加减乘除等操作。。

operator.h 文件

// copyright @ L.J.SHOU Mar.13, 2014// a simple calculator using Factory Design Pattern#ifndef OPERATOR_H_#define OPERATOR_H_#include <string>#include <iostream>#include <stdexcept>// base classclass Operator{public:  Operator(double lhs, double rhs)    : numberA(lhs), numberB(rhs){}  virtual double GetResult() = 0;protected:  double numberA;  double numberB;};// "+" class OperatorAdd : public Operator{public:  OperatorAdd(double lhs, double rhs)    : Operator(lhs, rhs) { }  double GetResult() { return numberA + numberB; }};// "-"class OperatorMinus : public Operator{public:  OperatorMinus(double lhs, double rhs)    : Operator(lhs, rhs) { }    double GetResult() { return numberA - numberB; }};// "*"class OperatorMul : public Operator{public:  OperatorMul(double lhs, double rhs)    : Operator(lhs, rhs) { }    double GetResult() { return numberA * numberB; }};// "/"class OperatorDiv : public Operator{public:  OperatorDiv(double lhs, double rhs)    : Operator(lhs, rhs) { }    double GetResult() {     if(numberB == 0)        throw std::runtime_error("divide zero !!!");    return numberA / numberB;   }};// factory functionOperator* createOperator(std::string oper, double lhs, double rhs){  Operator* pOper(NULL);   if(oper == "+")  {    pOper = new OperatorAdd(lhs, rhs);  }  else if(oper == "-")  {    pOper = new OperatorMinus(lhs, rhs);  }  else if(oper == "*")  {    pOper = new OperatorMul(lhs, rhs);  }  else if(oper == "/")  {    pOper = new OperatorDiv(lhs, rhs);  }  else  {    std::cerr << "not a valid operator" << std::endl;return NULL;  }  return pOper;}#endif

operator.cc 文件

// copyright @ L.J.SHOU Mar.13, 2014// a simple calculator using Factory Design Pattern#include "operator.h"#include <iostream>#include <stdexcept>#include "boost/shared_ptr.hpp"using namespace std;int main(void){  try{    boost::shared_ptr<Operator> pOper(createOperator("+", 0, 1));    cout << pOper->GetResult() << endl;    pOper = boost::shared_ptr<Operator>(createOperator("-", 0, 1));    cout << pOper->GetResult() << endl;    pOper = boost::shared_ptr<Operator>(createOperator("*", 2, 3));    cout << pOper->GetResult() << endl;    pOper = boost::shared_ptr<Operator>(createOperator("/", 1, 0));    cout << pOper->GetResult() << endl;  }  catch(std::runtime_error err){    std::cout << err.what()               << std::endl;  }  return 0;}

参考：

大话设计模式

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