Summary of knowledge points of objects and classes

1.OOP characteristic ： abstract , Encapsulation and data hiding , polymorphic , Inherit , Code reusability
2. Class declaration and class method definition Class declarations describe data parts as data members , Describe the common interface with the method of member function . Class method definition ： Describes how to implement class member functions .
3.C++ Interfaces are often （ Class definition ） Put it in the header file , Put the interface implementation in the source code . Common class names are capitalized .
4. Be careful ,class Declare a class , Pay attention to distinguish from the template , The template can be class typename Statement , Class, but not typename.
5. There are three kinds of permissions in the class ：private public protected among protected Related to inheritance . and private Often data members .public Often member functions . The member function is the interface between data members and the outside world , bridge .
6. The only difference between structure and class is , The default value in the structure is public, The default in the class is private.
7. Inline function ： Functions whose function definitions are in the class declaration will become inline functions . You can also define inline functions outside the class declaration , But it must be preceded by inline keyword .

class Stock
{
    
private:
       void set_tot();
};
inline void Stock::set_tot()
{
    
total_val = shares * share_val;
}

8. Different objects of the same class have their own storage space -> There is its own member variable inside , But member functions are common to all objects of this class .

Class constructor and destructor

1. Because the data variable is private, No direct access , All classes cannot be initialized with the method of structure initialization .-> Class constructors are born .
2. Note the following points when using class constructors ： The arguments to the constructor do not represent class members , But the values assigned to class members . Data member names generally use prefixes m_.
3. When designing a class , Generally, a default constructor that implicitly initializes all class members should be provided .
4. The destructor is added before the class name ~. commonly new After that, we will use the destructor delete Delete .
5.

 Insert a code chip here 
stock1 = Stock（“”,“”,“”）

Create a temporary variable assigned to stack1, But the destructor is called automatically when the temporary variable is not called .

6. The object created first calls destructor to delete base note. .
7. Initializing an object is more efficient than creating a temporary variable assignment to an object , Because there is no need to add another copy .
8.

 Because some functions have no parameters in parentheses , Add... After the function const
void stock::show()const

matters needing attention ：const Member objects can only be called const Member functions , When a member variable in a class +mutable after , Its value can be modified in constant objects and constant functions .

this The pointer
When two objects are involved , For example, it is used when comparing a data member of two objects this The pointer .
this Pointer to the object used to call the member function
1. When the return type is reference, it means that the calling object itself is returned , Not a copy .
2. Object array creation process ： First create the object with the default constructor and save it in the array , Reuse stock{} Create temporary objects in , Then assign values to the elements in the array . All object arrays must have a default constructor when they are created .

Class scope ：
Class scope means that members cannot be accessed directly from the outside , Class scope resolution operator must be added ::