Classes in C + +

Summary: When looking at QT, where: in the. cpp file (the source file for the Class)---Implement the slot and declare the slot in the. h file. So I intend to learn as much as possible about the classes in the C + + language in this essay.

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I.---classes and objects in section 10.3 of the Wu Guofeng and Wu Shanli Editor in the C + + programming code1. Declaration of class and object definition 1) class

The class is actually a new type of data. It is the combination of data and actions that work on the data (the basic tool for encapsulation and data hiding).

1 //description of a date class2 3 classcdata{4      Public:    5         voidSetDate (Inty, Intm,intd)6         intisleap year ();7         voidprint ();8     Private:9         intYear,month,day;Ten  One     protected: A         ....; -  -};

Description

• A class is a user-defined data type that does not allow initialization of a defined data member because it does not have storage space later. The data and functions defined in a class are called data members and function members.
• Access control properties: Define private permissions by default

Public: declares the outer interface of a class, which is a member that an external object of the class can access.

Private: allows access only to members of this class, and any access outside the class is illegal .

Protection (Protected): Similar to private types, the difference is that the new class access rights generated during the inheritance process are different .

2) Definition of object

1#include <iostream>2 classrectangle{3     Private:4         intw,h;5      Public:6         voidInput () {cin>>w,h};7         intArea () {returnh*W};8 };9 Ten voidMainvoid) One { A rectangle a,b,c; -cout<<"Please enter the length and width of the first rectangle:"; - a.input (); thecout<<"Please enter the length and width of the second rectangle:"; - b.input (); -cout<<"Please enter the length and width of the third rectangle:"; - c.input (); +     intsum; -Sum=a.area () +b.area () +C.area (); +count<<"the sum of the area of three rectangles is"sum<<Endl; A}

Note: A. "." The operator is used between the object and the member; the "::" operator is used between the class and its members;

　　　B. Encapsulation of a class---public, protected members in an object are not allowed to be accessed directly by non-member functions.

2. Constructors and destructors

1       classClock2         {3          Public:4Clock (intNEWH,intNEWM,intNewS);//constructor Function5                   voidSetTime (intNEWH,intNEWM,intNewS);6                   voidShowTime ();7         Private:8                   intHour, Minute, Second;9         };Ten  One the implementation of the constructor: A  -Clock::clock (intNEWH,intNEWM,intNewS) -         { theHour=NEWH; -Minute=newm; -Second=NewS; -         } +  - constructor functions when an object is created: +  A         intMain () at         { -Clock C (0,0,0);//implicitly calls the constructor and takes the initial value as an argument.  - c.showtime (); -                 return 0; -}

Description: The constructor----initializes the object with the given value when the object is created. The function that the system calls automatically when it is created.

• A function member with the same name as a class is called a---constructor, and its purpose is to initialize the object.
• Cannot specify return type (including void type)
• A class can define multiple constructors, with parameters or without parameters;
• If there is no constructor in the class, then the compiler will automatically create a parameterless constructor;
• The constructor is automatically called when the object is created

----------------------------Destructors

is a function that is automatically called by the system when an object is disposed.  function--- do a series of cleanup work before releasing an object.  Usually used to do the cleanup work of the Undo object. such as releasing memory allocated by the constructor

Classes in C + +