In insect classes and objects

Scope of class

== Class defines a new scope ==, All members of a class are in the scope of the class . Define members outside the class , Need to use ==:: Scope resolver == Indicate which class domain the member belongs to

Class instantiation

The process of creating objects with class types , Called class instantiation

1. == Class is just a model == The same thing , Defines which members of the class , Define a class == No actual memory space allocated == To store it
2. A class can instantiate multiple objects ,== Instantiated object Take up actual physical space , Store class member variables ==
3. Let's make an analogy .== Class to instantiate an object is like building a house out of a building plan , Class is like a blueprint ==, Just design what you need , But there are no physical buildings , The same class is just a design , Only the instantiated object can actually store data , Take up physical space

How class objects are stored

Object contains the members of the class

defects ： The member variables in each object are different , But call the same function , If stored in this way , When a class creates multiple objects ,== A copy of the code is saved in each object , Save the same code multiple times , Waste space . So what's the solution ？==

Save only member variables , Member functions are stored in public code snippets

== The size of a class , In fact, it is in this class ” Member variables ” The sum of the , Of course, memory alignment is also necessary , Notice the size of the empty class , Empty classes are special , The compiler gives an empty class a byte to uniquely identify the class .==

Structure memory alignment rules

1. The first member is offset from the structure by 0 The address of .
2. Other member variables are aligned to a number （ Align numbers ） An integral multiple of the address of . == Be careful ： Align numbers = Compiler default alignment number And The smaller value of the member size .==
   VS The default alignment number in is 8
3. The total size of the structure is ：== Maximum number of alignments （ The maximum of all variable types and the minimum of default alignment parameters ） Integer multiple .==
4. If the structure is nested , The nested structure is aligned to an integral multiple of its maximum alignment , The overall size of the structure is
   All maximum alignments （ The number of alignments with nested structures ） Integer multiple .

this The pointer

this Pointer leading out

At this point, someone should say that they are accessing the same function , So how to visit their respective dates

this The properties of the pointer

1. this The type of pointer ： Class types * const
2. Only in “ Member functions ” Internal use of
3. ==this Pointer is essentially a parameter of a member function ==, When an object calls a member function , Pass the object address as an argument to this Shape parameter . therefore == Objects are not stored this The pointer ==.
4. ==this Pointer is the first implied pointer parameter of a member function , Generally, the compiler passes through ecx Register auto transfer , No need for user delivery ==

【 Interview questions 】

==this Where does the pointer exist ？==

this The pointer is stored in the stack , because this It's a parameter , Parameters , Local variables are in the stack . But different compilers have some differences , Even different versions of the same compiler will be a little different , such as vs13 It's using ecx Register stored ,vs19 It's using rcx Register stored

==this Can the pointer be null ？==

Look at a disgusting question before you say this

therefore this Cannot be null pointer , Null pointer compilation does not report errors , Because he is not a grammatical error , The compiler can't check