【c++】类和对象（七）

🔥个人主页：Quitecoder

🔥专栏：c++笔记仓

朋友们大家好，本篇文章来到类和对象的最后一部分

目录

• 1.static成员
• • 1.1特性
  • 2.友元
  • • 2.1引入：的重载
    • 2.2友元函数
    • 2.3友元类
    • 3.内部类
    • 4.匿名对象
    • 5.拷贝对象时的一些编译器优化

      1.static成员

      声明为static的类成员称为类的静态成员，用static修饰的成员变量，称之为静态成员变量；用static修饰的成员函数，称之为静态成员函数。静态成员变量一定要在类外进行初始化

      例题：统计A类型创造了多少个对象

      class A
      {
      public:
      	A()
      	{}
      	A(const A& a)
      	{
      	}
      private:
      };
      A Func()
      {
      	A aa;
      	return aa;
      }
      int main()
      {
      	A aa1;
      	A aa2;
      	Func();
      	return 0;
      }
      

      我们的方法之一就是统计构造函数调用了多少次，我们就需要全局变量

      int n = 0;
      class A
      {
      public:
      	A()
      	{
      		++n;
      	}
      	A(const A& a)
      	{
      		++n;
      	}
      private:
      };
      A Func()
      {
      	A aa;
      	return aa;
      }
      int main()
      {
      	A aa1;
      	A aa2;
      	Func();
      	cout 
      public:
      	A()
      	{
      		++n;
      	}
      	A(const A& a)
      	{
      		++n;
      	}
      private:
       int n =0;
      };
      
      public:
      	A()
      	{
      		++n;
      	}
      	A(const A& a)
      	{
      		++n;
      	}
      private:
      	static int n;
      };
      int A::n = 0;
      
      public:
      	A()
      	{
      		++n;
      	}
      	A(const A& a)
      	{
      		++n;
      	}
      	static int Getn()
      	{
      		return n;
      	}
      private:
      	static int n;
      };
      
      public:
      Date(int year, int month, int day)
           : _year(year)
           , _month(month)
           , _day(day)
       {}
      private:
       int _year;
       int _month;
       int _day;
      };
      
      	out 
      public:
      	Date(int year, int month, int day)
      		: _year(year)
      		, _month(month)
      		, _day(day)
      	{}
      	void operator
      		out 
      public:
      	Date(int year, int month, int day)
      		: _year(year)
      		, _month(month)
      		, _day(day)
      	{}
      	
      //private:
      	int _year;
      	int _month;
      	int _day;
      };
      void operator
      	out 
      	Date d1(2005, 6, 23);
      	cout 
      	out 
       _cin  d._year;
       _cin  d._month;
       _cin  d._day;
       return _cin;
      }
      
       friend ostream& operator}
      private:
       int _year;
       int _month;
       int _day;
      };
      
      	friend class Date;
      public:
      	Time(int hour = 0, int minute = 0, int second = 0)
      		: _hour(hour)
      		, _minute(minute)
      		, _second(second)
      	{}
      private:
      	int _hour;
      	int _minute;
      	int _second;
      };
      class Date
      {
      public:
      	Date(int year = 1900, int month = 1, int day = 1)
      		: _year(year)
      		, _month(month)
      		, _day(day)
      	{}
      	void SetTimeOfDate(int hour, int minute, int second)
      	{
      		// 直接访问时间类私有的成员变量
      		_t._hour = hour;
      		_t._minute = minute;
      		_t._second = second;
      	}
      private:
      	int _year;
      	int _month;
      	int _day;
      	Time _t;
      };
      
      private:
      	static int k;
      	int h;
      public:
      	class B // B天生就是A的友元
      	{
      	public:
      		void fun(const A& a)
      		{
      			cout 
      	A::B b;
      	b.fun(A());
      	return 0;
      }
      
      public:
      	A(int a = 0)
      		:_a(a)
      	{
      		cout 
      		cout 
      public:
          A(int a = 0)
              :_a(a)
          {
              cout 
              cout 
          A();
          return 0;
      }
      
      public:
       int Sum_Solution(int n) {
       //...
       return n;
       }
      };
      int main()
      {
      	Solution().Sum_Solution(10);
      	return 0;
      }
      
      public:
      	A(int a = 0)
      		:_a(a)
      	{
      		cout 
      		cout 
      		cout 
      			_a = aa._a;
      		}
      		return *this;
      	}
      	~A()
      	{
      		cout }
      A f2()
      {
      	A aa;
      	return aa;
      }
      
      	const A& aa2 = 2;
      	return 0;
      }
      }
      int main()
      {
      	f1(A(2));
      	return 0;
      }
      
      	A aa;
      	return aa;
      }
      int main()
      {
      	f2();
      	return 0;
      }
      
      	A aa;
      	return aa;
      }
      int main()
      {
      	A aa2 = f2();
      	return 0;
      }
      
      	A aa;
      	return aa;
      }
      int main()
      {
      	A aa1;
      	aa1 = f2();
      	return 0;
      }