重在类型转换符

C/C++ code

 
 //baselength.h 
 #ifndef BASELENGTH_H 
 #define BASELENGTH_H 
  
 class BaseLength { 
 public: 
 explicit BaseLength(double h=0.0); 
 virtual double length() const; 
 virtual ~BaseLength(); 
 BaseLength(const BaseLength& a); 
 protected: 
 double haome; 
 }; 
  
 class Inches : public BaseLength { 
 public: 
 explicit Inches(double h=0.0); 
 virtual double length() const; 
 virtual ~Inches(); 
 Inches(const Inches& b); 
 /********************* 
         operator Meters() const; 
 operator Yards() const; 
 operator Perches() const; 
         **********************/ 
 }; 
  
 class Meters : public BaseLength { 
 public: 
 explicit Meters(double h=0.0); 
 virtual double length() const; 
 virtual ~Meters(); 
 Meters(const Meters& c); 
 }; 
  
 class Yards : public BaseLength{ 
 public: 
 explicit Yards(double h=0.0); 
 virtual double length() const; 
 virtual ~Yards(); 
 Yards(const Yards& d); 
 }; 
  
 class Perches : public BaseLength{ 
 public: 
 explicit Perches(double h=0.0); 
 virtual double length() const; 
 virtual ~Perches(); 
 Perches(const Perches& e); 
 }; 
  
 #endif 
  
 //baselength.cpp 
 #include  <iostream> 
  
 #include "baselength.h" 
  
 using std::endl; 
 using std::cout; 
  
 BaseLength::BaseLength(double h) : haome(h) { 
 cout < <"BaseLength called!" < <endl; 
 } 
  
 double BaseLength::length() const { 
 return haome; 
 } 
  
 BaseLength::~BaseLength() { 
 cout < <"aa" < <endl; 
 } 
  
 BaseLength::BaseLength(const BaseLength& a) { 
 haome=a.haome; 
 } 
  
 Inches::Inches(double h) : BaseLength(h*25.4) { 
 cout < <"Inches called!" < <endl; 
 } 
  
 Inches::Inches(const Inches& b) { 
 haome=b.haome; 
 } 
  
 Inches::~Inches() { 
 cout < <"bb" < <endl; 
 } 
  
 /*********** 
 operator Meters() const { 
 return Meters a(haome); 
 } 
  
 operator Yards() const { 
 return Yards a(haome); 
 } 
  
 operator Perches() const { 
 return Perches a(haome); 
 } 
 **********/ 
  
  
 double Inches::length() const { 
 return haome/25.4; 
 } 
  
 Meters::Meters(double h) : BaseLength(h*1000) { 
 cout < <"Meters called!" < <endl; 
 } 
  
 Meters::Meters(const Meters& c) { 
 haome=c.haome; 
 } 
  
 Meters::~Meters() { 
 cout < <"ccc" < <endl; 
 } 
  
 double Meters::length () const { 
 return haome/1000; 
 } 
  
  
 Yards::Yards(double h) : BaseLength(h*36*25.4) { 
 cout < <"Yards called!" < <endl; 
 } 
  
 Yards::~Yards() { 
 cout < <"ddd" < <endl; 
 } 
  
 Yards::Yards(const Yards& d) { 
 haome=d.haome ; 
 } 
  
  
 double Yards::length() const { 
 return haome/25.4/36; 
 } 
  
 Perches::Perches(double h) : BaseLength(h*5.5*36*25.4) { 
 cout < <"Perches called!" < <endl; 
 } 
  
 Perches::~Perches() { 
 cout < <"eee" < <endl; 
 } 
  
 Perches::Perches(const Perches& e) { 
 haome=e.haome; 
 } 
  
 double Perches::length() const { 
 return haome/25.4/36/5.5; 
 } 
  
  
 //main.cpp 
 #include  <iostream> 
  
 #include "baselength.h"  
 
  
 using std::endl; 
 using std::cout; 
 using std::cin; 
  
 int main() { 
 cout < <"read a haome at baselength!" < <endl; 
 double g=0.0; 
 cin>>g; 
     BaseLength a(g); 
 cout < <a.length() < <endl; 
  
 cout < <"read a inches at inches!" < <endl; 
 cin>>g; 
 Inches b(g); 
 cout < <b.length() < <endl; 
 cout < <b.BaseLength::length() < <endl; 
         /*********** 
         Meters v=b; 
         cout < <v.length() < <endl; 
         *************/ 
  
 cout < <"read a yards at Yards!" < <endl; 
 cin>>g; 
 Yards c(g); 
 cout < <c.length() < <endl; 
 cout < <c.BaseLength::length () < <endl; 
  
 cout < <"read a perches at perches!" < <endl; 
 cin>>g; 
 Yards d(g); 
 cout < <d.length() < <endl; 
 cout < <d.BaseLength::length() < <endl; 
  
 cout < <"read a meters at Meters!" < <endl; 
 cin>>g; 
 Meters e(g); 
 cout < <e.length() < <endl; 
 cout < <e.BaseLength::length() < <endl; 
 g=0.0; 
  
 return 0; 
 }