Chapter 14 class part 1

14.1 Member functions 、 Object replication and private members

14.1.1 Related foundations of classes

1. Composition of classes ： Member variables and member functions ;

2. Accessing members of a class , If you use class objects to access , So it's “ Object name . Member name ”; If it is a pointer to an object to access , So it's “ Pointer name -> Member name ”;

3 struct and class The difference between ：

1. struct and class You can customize the data type , Inheritance operations are also supported .
2. struct The default access level in is public, The default inheritance level is also public;class The default access level in is private, The default inheritance level is also private.
3. When class Inherit struct perhaps struct Inherit class when , The default inheritance level depends on class or struct In itself , class（private Inherit ）,struct（public Inherit ）, That is, it depends on the default inheritance level of the derived class .

tip： It is recommended to set the member only variable to struct;

14.1.2 Member functions

Definition of member function ：

class Time {
    
public:
	int Hour;
	int Minute;
	int Second;
	void initTime(int tmphour, int tmpmin, int tmpsec) // Member functions 
	{
    
		Hour = tmphour;
		Minute = tmpmin;
		Second = tmpsec;
	}

14.2 Constructors 、explicit And initialization list

14.2.1

How to write a constructor

class A
{
    
    public:
    {
    
        void myfunc()
        {
    
           Implementation code 
        }
    }
}
// How to write it 2
class A
{
    
    public:
    {
    
        void myfunc()
        
    }
}
void A::myfunc()
{
    
    Implementation code 
}

14.2.2 Constructors

1. Constructor is automatically called when creating class object ;
2. The constructor is to initialize the data members of the class

Implementation of constructor ：

Time::Time(int tmphour, int tmpmin, int tmpsec)
				:Hour(tmphour),Minute(tmpmin) // This is called constructor initialization list 

{
    
	Hour = tmphour;					
	Minute = tmpmin;
	Second = tmpsec;
	initMillTime(0);
}

matters needing attention ：1. Constructor has no return value
2. Constructors cannot be called manually
3. Constructor is public function , Because he will be called by the system
4. Constructor if there are parameters , Then it should also have corresponding parameters when creating objects

Time myTime = Time(12, 13, 52);
		Time myTime2(12, 13, 52);
		Time myTime3 = Time{
     12, 13, 52 };
		Time myTime4{
     12, 13, 52 };
	// Time myTime5 = { 12, 13, 52 };

		//Time myTime6(); // It can be , No parameters , It may be mistaken by the compiler for a function declaration 
		//Time myTime7(12, 13); // Can not be , Lack of parameter  

14.2.3 Multiple constructors

A class can provide multiple construction parameters , It means that you can provide multiple creation methods for this class ;

14.2.4 Function default parameters

If the constructor is written as follows

Time::Time(int tmphour, int tmpmin, int tmpsec=12)

Then you can pass only two parameters to the constructor ;

14.2.5 Implicit transformation sum explicit

add explicit The declaration indicates that the constructor must perform a display conversion ;