虚函数和纯虚函数之间的差异 [英] Difference between a virtual function and a pure virtual function

问题描述

可能重复：

C ++虚拟/纯虚拟解释

纯虚函数和虚函数之间？

What is the difference between a pure virtual function and a virtual function?

我知道纯虚函数是一个没有主体的虚函数，但是这意味着什么，实际上是由下面的行做的：

I know "Pure Virtual Function is a Virtual function with no body", but what does this mean and what is actually done by the line below:

virtual void virtualfunctioname() = 0

推荐答案

一个虚函数使其类成为一个多态基类。派生类可以覆盖虚函数。通过基类指针/引用调用的虚函数将在运行时解析。也就是说，使用对象的动态类型代替其静态类型

A virtual function makes its class a polymorphic base class. Derived classes can override virtual functions. Virtual functions called through base class pointers/references will be resolved at run-time. That is, the dynamic type of the object is used instead of its static type:

 Derived d;
 Base& rb = d;
 // if Base::f() is virtual and Derived overrides it, Derived::f() will be called
 rb.f();  

纯虚函数是一个虚函数，声明以 = 0 ：

A pure virtual function is a virtual function whose declaration ends in =0:

class Base {
  // ...
  virtual void f() = 0;
  // ...

一个纯虚函数隐式地使它被定义为 abstract （与在Java中你有一个关键字来显式地声明类abstract）不同。抽象类不能实例化。派生类需要重写/实现所有继承的纯虚函数。如果他们没有，它们也会变得抽象。

A pure virtual function implicitly makes the class it is defined for abstract (unlike in Java where you have a keyword to explicitly declare the class abstract). Abstract classes cannot be instantiated. Derived classes need to override/implement all inherited pure virtual functions. If they do not, they too will become abstract.

C ++的一个有趣的特性是，一个类可以定义一个具有实现的纯虚函数。
（有用的是有争议的。）

An interesting 'feature' of C++ is that a class can define a pure virtual function that has an implementation. (What that's good for is debatable.)

注意，C ++ 11为 delete 和默认关键字看起来类似于纯虚函数的语法：

Note that C++11 brought a new use for the delete and default keywords which looks similar to the syntax of pure virtual functions:

my_class(my_class const &) = delete;
my_class& operator=(const my_class&) = default;

请参阅此问题和这一个了解有关使用 delete 的更多信息和默认。

See this question and this one for more info on this use of delete and default.

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