13.inline,const,mutable,this,static

One ： Implementing member functions in class definitions inline： The implementation of a member within a class is also called a function within a class
This kind of member function implemented directly in the definition of class , Will be regarded as inline Inline functions to handle .

Two ： At the end of a member function const

const :  Constant , Add a after the member function  const. Not only to add... In the member function declaration  const , Also add to the member function definition  const;
 effect ： Tell the system , This member function   It will not modify the value of any member variable in the object, etc . in other words , This member function does not modify any state of the class .
 Add one behind your ass const Suffix member function  " Constant member functions ";

const time abc;		 Definition const object , This object has limitations .
abc.initMillTime(1500);			 Can not be ,initMillTime() Not at all  const  Member functions , This initMillTime()  Can only be non const Object call .

time def;
def.initMillTime(1500);

const  Member functions , No matter what  const  object , Or not  const, Fine  const, You can call  const  member .
 Instead of const Member functions , Can't be  const  Object call , Can only be given  const  Object call .

void ptfunc() const
{
	return;
}
 Report errors ,const Can only load member functions , You can't add it to an ordinary function 

3、 ... and ：mutable( unstable , Easy to change ),const The antonym of .mutable The introduction of is just to break through const The limitation of .

 use  mutable  Modify a member variable , Once a member variable is  mutable  modification . It means , This member variable is always in a state that can be modified ,
 Even in the  const  In the member function at the end , You can also modify .

Four ： Returns a reference to its own object ,this.
class time{
public:
int hour;
int minute;
int second;

		static int mystatic;     Declare static member variables , Memory has not been allocated yet , So you can't initialize here .
								 In another .cpp The document defines  int time::mystatic = 15;  Definition is not required  static.
		static void mstafunc(int testvalue);
								 In another .cpp The document defines  void time::mstafunc(int testvalue){}
								static  Member functions cannot modify non members  static  Member variables , It can only be modified  static  Member variables of .

		void initTime(int tmphour,int tmpmin, int tmpsec){
			hour = tmphour;
			minute = tmpmin;
			second = tmpsec;
		}
	public:
		time& add_hour(int tmphour){ 		
			hour += tmphour;		this->hour += tmphour
			return *this;	 Return the object itself 
		} 
		time& add_minute(int minute){ 		
			this->minute += minute;		
			return *this;
		}   
	};

time mytime;
mytime.add_hour(3).add_minute(12);

 How to understand  this ( Reserved words ), When we call member functions , The compiler is responsible for the address of this object (&mytime) Passed to a hidden  this  Shape parameter .
 From a system perspective , Direct access to class members is considered through  this  Implicitly called .

 Internal practices of the compiler 
	time& add_hour(time *this, int tmphour){ 		
			this->hour += tmphour;
			hour += tmphour;    
			return *this;	 Return the object itself 
		}  

	time mytime;
	mytime.add_hour(&mytime,3);

(1)this Pointers can only be used in member functions , Global function , Static functions cannot be used  this  The pointer .
(2) In ordinary member functions ,this  Is pointing to the non  const  Object's  const  The pointer ( The type is time, that  this  Namely  time *const this), Express  this  Can only point to objects  time  Object call .
(3) stay  const  In member function , this  The pointer is a point  const  Object's  const  The pointer  ( The type is time,this Namely  const time *const this  Pointer to type ) 

5、 ... and ：static member
There are member variables belonging to the entire class , This member variable is called static Member variables .

 characteristic : Does not belong to an object , Belong to the whole class , Once we change the value of this member variable in an object , The result of the modification can be seen directly in other objects .
	  There is only one copy of this member variable , Reference to this member variable , We're going to use       Class name :: Member variable name 
	  Member functions can also be preceded by  static  constitute , Static member functions . Member functions belonging to the entire class . Invocation time        Class name :: Member function name 

 How to define static   Member variables ( Allocate memory )？
	 We usually go to a certain .cpp This static member variable is defined at the beginning of the source file . This ensures that the static member variable has been successfully initialized before calling any function .

void func(){
	static int abc = 5;     Local static variable 
}
static int g_abc = 15;     Also stored in static storage . Limiting this global quantity can only be used in this document .

extern int g_abc = 0;

Reference static member variables
cout << time::mystatic << endl;

time mytime1;
mytime1.mystatic = 40;
time mytime2;

cout << time::mystatic <<endl;
cout << mytime1.mystatic << endl;
cout << mytime2.mystatic << endl;		 Values are 40


time::mystatic(12);
mytime1.mstafunc(15);
mytime2.mstafunc(78);