抽象方法和纯虚函数是相同的东西吗？ [英] Are abstract methods and pure virtual functions the same thing?

问题描述

据我所知，抽象方法和纯虚函数都不提供任何功能......所以我们可以说它们都是同样的东西？

另外，假设一个类（不一定声明为抽象）包含一些实现的方法（不是抽象的或虚拟的），但包含一个纯虚函数。这个类是抽象的吗？

解决方案

是，它们是相同的。在C ++中，抽象方法只是描述纯虚函数特征的另一种方式。这两者都只是一种没有实现的方法，只要在实际实例化类之前需要在子类中实现。

C ++中纯虚函数和抽象类的情况类似，它们实质上意味着完全相同的事情。任何抽象类都必须至少有一个纯虚函数，否则它可能被实例化并且不会是抽象的。同样，任何至少有一个纯虚函数的类都必须是抽象的，因为它需要被扩展，以便实际上可以实现该方法。

因此，一个类是抽象的当且仅当至少包含1个纯虚函数/抽象方法。

稍后，像Java和C＃这样的语言使得这些更加明确，允许使用特殊的关键字来定义类抽象，而不是使用纯虚函数。 C ++可以让你和这些语言做同样的事情，但是它们只是更加明确一些。 ：D

As far as I know, both abstract methods and pure virtual functions do NOT provide any functionality ... So can we say they're both the same thing ?

Also, suppose a class (not necessarily declared as abstract) contains a number of implemented methods (not abstract or virtual), but contains a pure virtual function. Is this class then abstract ?

解决方案

Yes, they are the same thing. In C++, an abstract method is just another way of describing the characteristics of a pure virtual function. Both just mean a method with no implementation provided that needs to be implemented in a sub-class before the class can actually be instantiated.

The situation with pure virtual functions and abstract classes in C++ is similar as they essentially mean exactly the same thing. Any abstract class must have at least 1 pure virtual function or else it could be instantiated and wouldn't be abstract. Likewise, any class with at least 1 pure virtual function must be abstract because it needs to be extended so that method can actually be implemented.

Therefore, a class is abstract if and only if it contains at least 1 pure virtual function/abstract method.

Later on, languages like Java and C# made things like this more explicit, allowing a special keyword to define a class abstract rather than the presence of a pure-virtual function. C++ lets you do the same things as these languages, but they're just a little more explicit about it. :D

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