Lesson 24 Analysis of classical problems （ Construction and deconstruction sequence ）

One 、 Problem analysis

• problem ： When there are multiple objects in a program , How to determine the deconstruction order of these objects ？

  The order in which constructors are called when a single object is created

  • Call the construction process of the parent class

  • Call the constructor of a member variable （ Call order is the same as declaration order ）

    A class contains other classes , The calling order is in the order of declaration

  • Call the constructor of the class itself

    The destructor is called in the reverse order of the corresponding constructor

  • Be careful ： The above three are not independent , But called in this order

  For stack objects and global objects , It is similar to the order of entering and leaving the stack , The last constructed object first destructs

  Destructions of heap objects occur when delete When , And delete The order of use of

• problem ：const Keyword can modify the object of the class ？ If possible , what are you having? 1 characteristic ？

  const Keywords can decorate objects

  const The decorated object is a read-only object

  Member variables of read-only objects are not allowed to be changed

  System object is the concept of compilation stage , Invalid runtime

  C++ Medium const Member functions

  • const Object can only call const Member function of

  • const Only... Can be called in member functions const Member functions

  • const The value of a member variable cannot be overwritten directly in a member function

  • const Member function definition ：

    type calssname::function(type p) const

    Be careful ：

    const It's in the back

    The function declaration in the class and the function definition in the historical records must contain const keyword

• problem ： Do member functions and member variables belong to specific objects ？

  From the perspective of object oriented

  • Object by property （ Member variables ） And methods （ Member functions ） constitute

  From the perspective of program operation

  • Objects consist of data and functions , Data can be on the heap 、 Stack 、 And global data area , Functions can only be in code snippets

  So all objects share a set of member functions , Because member functions cannot be deleted

  Conclusion

  • Each object has its own independent properties （ Member variables ）
  • Methods of all objects sharing classes （ Member functions ）
  • Method can directly access the properties of an object
  • Method this Used to refer to the current object

  There is only one set of member functions , Member functions can access member variables in any class

Two 、 Summary

• The destruct order of objects is opposite to the construction order
• const Keywords can decorate objects , Get a read-only object
• Read only objects can only be called const Member functions
• All objects share the member functions of the class
• Hidden this Pointer is used to represent the current object