C++/Class/static

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Accessing static members using non-static member functions.

<source lang="cpp">

  1. include <iostream>

using namespace std; class Cat { public: 

  Cat(int age):itsAge(age){count++; }
  virtual ~Cat() { count--; }
  virtual int GetAge() { return itsAge; }
  virtual void SetAge(int age) { itsAge = age; }
  virtual int GetHowMany() { return count; }

private: 

  int itsAge;
  static int count;

}; int Cat::count = 0; int main() { 

  const int MaxCats = 5; int i;
  Cat *CatHouse[MaxCats];
  for (i = 0; i<MaxCats; i++)
     CatHouse[i] = new Cat(i);
  for (i = 0; i<MaxCats; i++)
  {
     cout << CatHouse[i]->GetHowMany();
     cout << CatHouse[i]->GetAge()+2;
     delete CatHouse[i];
     CatHouse[i] = 0;
  }
  return 0;

} 


 </source>


Accessing static members without an object.

<source lang="cpp">

  1. include <iostream>

using namespace std; class Cat { public: 

  Cat(int age):itsAge(age){count++; }
  virtual ~Cat() { count--; }
  virtual int GetAge() { return itsAge; }
  virtual void SetAge(int age) { itsAge = age; }
  static int count;

private: 

  int itsAge;

}; int Cat::count = 0; void TelepathicFunction(); int main() { 

  const int MaxCats = 5; int i;
  Cat *CatHouse[MaxCats];
  for (i = 0; i<MaxCats; i++)
  {
     CatHouse[i] = new Cat(i);
     TelepathicFunction();
  }
  for ( i = 0; i<MaxCats; i++)
  {
     delete CatHouse[i];
     TelepathicFunction();
  }
  return 0;

} void TelepathicFunction() { 

  cout << "There are ";
  cout << Cat::count << " cats alive!\n";

} 


 </source>


Calculate salary using static members.

<source lang="cpp">

  1. include <iostream>

using namespace std; class salary { public: 

  void init(const int b) {b_sal = b; your_bonus = 0;}
  void  calc_bonus(const double perc){ your_bonus = b_sal * perc; }
  static void  reset_all(const int p){ all_bonus = p; }
  int  comp_tot() const{ return (b_sal + your_bonus + all_bonus); }

private: 

  int         b_sal;
  int         your_bonus;
  static int  all_bonus;     //declaration

}; int salary::all_bonus = 100; int main() { 

  salary  w1, w2;
  w1.init(1000);
  w2.init(2000);
  w1.calc_bonus(0.2);
  w2.calc_bonus(0.15);
  salary::reset_all(400);
  cout << " w1 " << w1.comp_tot() << "   w2 "
       << w2.comp_tot() << endl;

} 


 </source>


Reference static method along with class name

<source lang="cpp">

  1. include <iostream>

using namespace std; class SomeClass { 

public:
  static void message(void) { cout << "Hello, world!\n"; } ;

}; int main(void) { 

  SomeClass::message();

} 


 </source>


static counter

<source lang="cpp">

  1. include <iostream>

using namespace std; class SomeClass { 

 public:
   static int count;
   SomeClass(int value) 
   { 
     count++; 
     my_data = value;
   }; 
   SomeClass(int value, int static_value) 
 {
     count = static_value;
     my_data = value; 
 };
   ~SomeClass(void) { count--; };
   int my_data;

}; int SomeClass::count; int main(void) 

{
  SomeClass One(1, 999); 
  cout << "One: " << One.my_data << " " << One.count << endl ;
  
  SomeClass Two(2);
  cout << "Two: " << Two.my_data << " " << Two.count << endl ;
  
  SomeClass Three(3);
  cout << "Three: " << Three.my_data << " " << Three.count << endl ;

} 


 </source>


static field is shared among instances

<source lang="cpp">

  1. include <iostream>

using namespace std; class SomeClass { 

 public:
   SomeClass(int value) { count++; my_data = value; }; 
   SomeClass(int value, int static_value) 
 {
     count = static_value; my_data = value; 
 };
   ~SomeClass(void) { count--; };
   void show_values(void) { cout << my_data << " " << count << endl; };
 private:  
   static int count;
   int my_data;

}; int SomeClass::count; int main(void) { 

  SomeClass One(1, 999); 
  One.show_values();   
  
  SomeClass Two(2, 1000);
  Two.show_values();
  SomeClass Three(3);
  Three.show_values();

} 


 </source>


static functions and ID numbers for objects

<source lang="cpp">

  1. include <iostream>

using namespace std; class gamma { 

  private:  
  static int total;        
     int id;                  
  public:  
     gamma(){  
        total++;              
        id = total;           
     }  
     ~gamma(){  
        total--;  
        cout << "Destroying ID number " << id  << endl;  
     }  
     static void showtotal(){  
        cout << "Total is " << total << endl;  
     }  
     void showid(){  
        cout << "ID number is " << id << endl;  
     }

}; int gamma::total = 0; int main(){ 

  gamma g1;  
  gamma::showtotal();  
 
  gamma g2, g3;  
  gamma::showtotal();  
 
  g1.showid();  
  g2.showid();  
  g3.showid();  
  return 0;

} 


 </source>


Static member data.

<source lang="cpp">

  1. include <iostream>

using namespace std; class Cat { public: 

  Cat(int age):itsAge(age){count++; }
  virtual ~Cat() { count--; }
  virtual int GetAge() { return itsAge; }
  virtual void SetAge(int age) { itsAge = age; }
  static int count;

private: 

  int itsAge;

}; int Cat::count = 0; int main() { 

  const int MaxCats = 5; int i;
  Cat *CatHouse[MaxCats];
  for (i = 0; i<MaxCats; i++)
     CatHouse[i] = new Cat(i);
  for (i = 0; i<MaxCats; i++)
  {
     cout << Cat::count;
     cout << CatHouse[i]->GetAge();
     delete CatHouse[i];
     CatHouse[i] = 0;
  }
  return 0;

} 


 </source>


Static member functions.

<source lang="cpp">

  1. include <iostream>

using namespace std; class Cat { public: 

  Cat(int age):itsAge(age){count++; }
  virtual ~Cat() { count--; }
  virtual int GetAge() { return itsAge; }
  virtual void SetAge(int age) { itsAge = age; }
  static int GetHowMany() { return count; }

private: 

  int itsAge;
  static int count;

}; int Cat::count = 0; void TelepathicFunction(); int main() { 

  const int MaxCats = 5;
  Cat *CatHouse[MaxCats]; int i;
  for (i = 0; i<MaxCats; i++)
  {
     CatHouse[i] = new Cat(i);
     cout << "There are " << Cat::GetHowMany() << " cats alive!\n";
  }
  for ( i = 0; i<MaxCats; i++)
  {
     delete CatHouse[i];
     cout << "There are " << Cat::GetHowMany() << " cats alive!\n";
  }
  return 0;

} 


 </source>


static members in classes

<source lang="cpp">

  1. include <iostream>

using namespace std; class CDummy { 

 public:
   static int n;
   CDummy () { n++; };
   ~CDummy () { n--; };

}; int CDummy::n=0; int main () { 

 CDummy a;
 CDummy b[5];
 CDummy * c = new CDummy;
 cout << a.n << endl;
 delete c;
 cout << CDummy::n << endl;
 return 0;

} 


 </source>


Static member variables and functions

<source lang="cpp">

  1. include <iostream>

using namespace std; class MyClass { public: 

   static int s_Total;   
   MyClass(int level = 0);
   static int GetTotal();

private: 

   int myLevel;

}; int MyClass::s_Total = 0; MyClass::MyClass(int level):myLevel(level) { 

   cout << "born!" << endl;
   ++s_Total;

} int MyClass::GetTotal() { 

   return s_Total;

} int main() { 

   cout << MyClass::s_Total << "\n\n";
   MyClass myObject1, myObject2, myObject3;
   cout << MyClass::GetTotal() << "\n";
   return 0;

} 


 </source>


Update static field in member method

<source lang="cpp">

  1. include <iostream>

using namespace std; class SomeClass { 

 public:  
   SomeClass(int value) { some_value = value; };
   void show_data(void) { cout << data << " " << some_value << endl; };
   static void set_data(int value) { data = value; };
 private:
   static int data;
   int some_value;

}; int SomeClass::data; int main(void) { 

  SomeClass my_class(1001);
  my_class.set_data(5005);
  my_class.show_data();

} 


 </source>


Using a static data member in a class

<source lang="cpp">

  1. include <iostream>
  using namespace std;
  class CBox                   
  {
     public:
        static int objectCount;
        CBox(double lv, double bv = 1.0, double hv = 1.0): m_Length(lv),
                                                           m_Breadth(bv),
                                                           m_Height(hv)
        {
           cout << "Constructor called.";
           objectCount++;
        }
        CBox()
        {
           cout << "Default constructor called.";
           m_Length = m_Breadth = m_Height = 1.0;
           objectCount++;
        }
        double Volume() const
        {
           return m_Length*m_Breadth*m_Height;
        }
     private:
        double m_Length;
        double m_Breadth;
        double m_Height; 
  };
  int CBox::objectCount = 0;
                            
  int main()
  {
     CBox boxes[5];         
     CBox cigar(8.0, 5.0, 1.0);
     cout << CBox::objectCount;
     cout << boxes[2].objectCount;
     return 0;
  }
 
   
 </source>
Источник — «http://cppe.ru/index.php?title=C%2B%2B/Class/static&oldid=1341»