以下是http://www.csdn.net/develop/Article/14/14487.shtm的一个改进版本,本来是作为评论附在上一篇文章后面的,但是作为评论发表的话,会丢失很多文字,很奇怪的说。本文是我和singleracer讨论的结果,个人认为几乎接近完美,希望能对大家有帮助,大家可以自己加入其它的单位体系和单位。
计量的模板类:
#ifndef _QUANTITY_H_ #define _QUANTITY_H_
#ifdef _DEBUG #define ASSERT_SAME_TYPE( T1, T2) do {T1 v=T2();v; }while(false) #else #define ASSERT_SAME_TYPE( T1, T2) #endif
#include "singleton.h"
template<class UnitType> struct UnitTraits { typedef UnitType::Validator Validator; };
template<class ValueType> class ValueTraits { public: static bool equal(const ValueType & l, const ValueType & r) {return (l == r);} };
template<> class ValueTraits<double> { public: static bool equal(const double & l, const double & r) { static double precision = 0.000000001; return (l - r < precision); } };
template<> class ValueTraits<float> { public: static bool equal(const float & l, const float & r) { static float precision = 0.000000001f; return (l - r < precision); } };
template<typename ValueType, class UnitValidator, class _Traits = ValueTraits<ValueType> > class Quantity { public: typedef UnitValidator Validator;
template<typename UnitType>Quantity(const ValueType & amount, const UnitType & ) : m_amount(amount), m_unit(Singleton< unit_wrap<UnitType, ValueType> >::Instance()) { ASSERT_SAME_TYPE(UnitTraits<UnitType>::Validator, Validator); } ~Quantity() { } Quantity(const Quantity & other) : m_amount(other.m_amount), m_unit(other.m_unit) { } Quantity & operator=(const Quantity & rhs) { if(&rhs != this) { m_amount = rhs.m_amount; m_unit = rhs.m_unit; } return *this; } template<typename UnitType> void convert(const UnitType & ) { ASSERT_SAME_TYPE(UnitTraits<UnitType>::Validator, Validator); unit_base<ValueType> * unit = Singleton< unit_wrap<UnitType, ValueType> >::Instance(); if(unit != m_unit) { m_amount = m_unit->to_standard(m_amount); m_unit = unit; m_amount = m_unit->from_standard(m_amount); }
} Quantity & operator+=(const Quantity & rhs) { m_amount += unitize( rhs ); return *this; } Quantity & operator-=(const Quantity & rhs) { m_amount -= unitize( rhs ); return *this; } bool operator==(const Quantity & rhs) { return _Traits::equal( m_amount, unitize(rhs)); } bool operator>(const Quantity & rhs) { return m_amount > unitize( rhs ); } bool operator>=(const Quantity & rhs) { return (m_amount > unitize( rhs ) ? true : (equal( m_amount, unitize(rhs))) ); } bool operator<(const Quantity & rhs) { return m_amount < unitize( rhs ); } bool operator<=(const Quantity & rhs) { return (m_amount < unitize( rhs ) ? true : (equal( m_amount, unitize(rhs))) ); }
private: // 对于单位相同的运算不需要转换,也就没有丢失精度的问题 ValueType unitize( const Quantity & rhs ) { if( m_unit == rhs.m_unit ) return rhs.m_amount; else return m_unit->from_standard(rhs.m_unit->to_standard(rhs.m_amount)); }
private: template<typename ValueType> class unit_base { public: virtual ValueType to_standard(const ValueType & val) const = 0; virtual ValueType from_standard(const ValueType & val) const = 0; }; // 把unit_wrap设计为singleton,这样比较单位是否相同只需作简单的指针比较 template<typename UnitType, typename ValueType> class unit_wrap : public unit_base<ValueType> { protected: unit_wrap() {} ~unit_wrap() {} public: virtual ValueType to_standard(const ValueType & val) const { return UnitType::to_standard(val); } virtual ValueType from_standard(const ValueType & val) const { return UnitType::from_standard(val); } };
private: ValueType m_amount; unit_base<ValueType> * m_unit; };
#define QUANTITY Quantity<ValueType,Validator,Traits> template<typename ValueType,typename Validator,typename Traits> QUANTITY inline _cdecl operator+(const QUANTITY & a, const QUANTITY & b) {return (QUANTITY(a)+=b);}
template<typename ValueType,typename Validator,typename Traits> QUANTITY inline _cdecl operator-(const QUANTITY & a, const QUANTITY & b) {return (QUANTITY(a)-=b);}
#endif /* _QUANTITY_H_ */
重量: #ifndef _WEIGHT_H_ #define _WEIGHT_H_
#include "../Quantity.h"
class WeightValidator {}; typedef Quantity<double, WeightValidator> Weight;
/* template<typename ValueType, typename UnitType> Weight inline _cdecl operator*(const ValueType& value, const UnitType& unit ) {return Weight(value, unit);} */
class Kilogram { public: typedef WeightValidator Validator; static double to_standard(double val) {return val;} static double from_standard(double val) {return val;} };
class Gramme { public: typedef WeightValidator Validator; static double to_standard(double val) {return val/1000.0;} static double from_standard(double val) {return val*1000.0;} };
Kilogram _kg; Gramme _g;
#endif /* _WEIGHT_H_ */
长度: #ifndef _LENGTH_H_ #define _LENGTH_H_
#include "../Quantity.h"
class LengthValidator {}; typedef Quantity<double, LengthValidator> Length;
/* template<typename ValueType, typename UnitType> Length inline _cdecl operator*(const ValueType& value, const UnitType& unit ) {return Length(value, unit);} */
class Meter { public: typedef LengthValidator Validator; static double to_standard(double val) {return val;} static double from_standard(double val) {return val;} };
class Kilometer { public: typedef LengthValidator Validator; static double to_standard(double val) {return val*1000.0;} static double from_standard(double val) {return val/1000.0;} };
Meter _m; Kilometer _km;
#endif /* _LENGTH_H_ */
测试代码: // Quantity.cpp : Defines the entry point for the console application. //
#include "stdafx.h" #include "weight.h" #include "length.h"
void testWeight() { Weight w1(1.0, _kg); //构造函数 Weight w2(1.0, _g); //构造函数
Weight w3 = w1; //拷贝构造函数 w3 = w2; //赋值操作
Weight w4(1.0, _kg); w4 += w1; //相同单位相加 w4 += w2; //不同单位相加 Weight w5 = w4 + w1; //相同单位相加 w5 = w4 + w2; //不同单位相加
Weight w6(2.0, _kg); w6 -= w1; //相同单位相减 w6 -= w2; //不同单位相减 Weight w7 = w5 - w1; //相同单位相减 w7 = w5 - w2; //不同单位相减
// 比较 Weight a(1.0, _kg); Weight b(2.0, _kg); Weight c(2000.0, _g); Weight d(3000.0, _g); bool f = (a < b); f = (a < c); f = (b==c); f = (b < d);
//单位换算 Weight w10(1.0, _kg); w10.convert(_g); w10.convert(_kg); }
void testLength() { Length l1(1.0, _km); //构造函数 Length l2(1.0, _m); //构造函数
Length l3 = l1; //拷贝构造函数 l3 = l2; //赋值操作
Length l4(1.0, _km); l4 += l1; //相同单位相加 l4 += l2; //不同单位相加 Length l5 = l4 + l1; //相同单位相加 l5 = l4 + l2; //不同单位相加
Length l6(2.0, _km); l6 -= l1; //相同单位相减 l6 -= l2; //不同单位相减 Length l7 = l5 - l1; //相同单位相减 l7 = l5 - l2; //不同单位相减
// 比较 Length a(1.0, _km); Length b(2.0, _km); Length c(2000.0, _m); Length d(3000.0, _m); bool f = (a < b); f = (a < c); f = (b==c); f = (b < d);
//单位换算 Length l10(1.0, _km); l10.convert(_m); l10.convert(_km); }
void testError() { #if(0) Weight w1; // 没有缺省构造函数 Length l1; // 没有缺省构造函数 #endif #if(0) Weight w2(1.0, _km); //错误的单位 Length l2(1.0, _g); //错误的单位 #endif #if(0) Weight w3(1.0, _kg); Length l3(1.0, _m); w3.convert(_km); //错误的单位 l3.convert(_g); //错误的单位 #endif #if(0) Weight w4(1.0, _kg); Length l4(1.0, _m); w4 += l4; //错误的类型 w4 -= l4; //错误的类型 #endif #if(0) Weight w5(1.0, _kg); Length l5(1.0, _m); bool f = (w5 == l5); f = (w5 > l5); f = (w5 < l5); #endif }
int main(int argc, char* argv[]) { testWeight(); testLength(); testError(); return 0; }

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