Chapter Summary

小结

Classes are the most fundamental feature in C++. Classes let us define new types that are tailored to our own applications, making our programs shorter and easier to modify.

类是 C++ 中最基本的特征，允许定义新的类型以适应应用程序的需要，同时使程序更短且更易于修改。

Data abstractionthe ability to define both data and function membersand encapsulationthe ability to protect class members from general accessare fundamental to classes. Member functions define the interface to the class. We encapsulate the class by making the data and functions used by the implementation of a class private.

数据抽象是指定义数据和函数成员的能力，而封装是指从常规访问中保护类成员的能力，它们都是类的基础。成员函数定义类的接口。通过将类的实现所用到的数据和函数设置为 private 来封装类。

Classes may define constructors, which are special member functions that control how objects of the class are initialized. Constructors may be overloaded. Every constructor should initialize every data member. Constructors should use a constructor initializer list to initialize the data members. Initializer lists are lists of namevalue pairs where the name is a member and the value is an initial value for that member.

类可以定义构造函数，它们是特殊的成员函数，控制如何初始化类的对象。可以重载构造函数。每个构造函数就初始化每个数据成员。初始化列表包含的是名—值对，其中的名是一个成员，而值则是该成员的初始值。

Classes may grant access to their nonpublic members to other classes or functions. A class grants access by making the class or function a friend.

类可以将对其非 public 成员的访问权授予其他类或函数，并通过将其他的类或函数设为友元来授予其访问权。

Classes may also define mutable or static members. A mutable member is a data member that is never const; its value may be changed inside a const member function. A static member can be either function or data; static members exist independently of the objects of the class type.

类也可以定义 mutable 或 static 成员。mutable 成员永远都不能为 const；它的值可以在 const 成员函数中修改。static 成员可以是函数或数据，独立于类类型的对象而存在。