blocks|key|1228194|text|例如，在使用Policy-based+design时，这是非常常见的。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1228195|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Policy-based_design^0|6|J|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

It's very common when using <a href="http://en.wikipedia.org/wiki/Policy-based_design" rel="noreferrer">Policy-based design</a>, for example.

blocks|key|878733|text|最容易指出的是iostream，它继承自istream和ostream。cin和cout分别是istream和ostream，但fstream派生自iostream。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|878734|entityMap^0|7|8|K|7|S|7|10|3|14|4|1B|7|1J|7|1S|7|22|8|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|G|$]]

Easiest to point at <code>iostream</code>, which inherits from <code>istream</code> and <code>ostream</code>. <code>cin</code> and <code>cout</code> are <code>istream</code> and <code>ostream</code> respectively but <code>fstream</code> derives from <code>iostream</code>.

blocks|key|2637672|text|微软的ATL+(活动模板库)使用多重继承作为混合类：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2637673|http://en.wikipedia.org/wiki/Active_Template_Library|offset|length|2637674|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1G|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

Microsoft's ATL (Active Template Library) uses multiple inheritance as mixin classes:

<a href="http://en.wikipedia.org/wiki/Active_Template_Library" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Active_Template_Library</a>

blocks|key|1228347|text|国际海事组织，这是值得商议的。在模板出现之前，有相当数量的案例证明了这一点。基本上，您可以使用基类，就像您可以通过模板使用策略类一样。例如，考虑如下模板：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1228348|template+<typename+policy1,+typename+policy2>
class+whatever+{
++++policy1+p1;
++++policy2+p2;
public:
++++void+dosomething()+{+if+(p1.enquire())+p2.dosomething();+}
};|code-block|syntax|javascript|1228349|如果你出于某种原因不想使用模板，你可以通过多重继承获得(一些)非常相似的功能：|1228350|class+whatever+:+policy1,+policy2+{+++
++++void+dosomething()+{+if+(enquire())+dosomething();++}|1228351|}；|1228352|在这两种情况下，基本上都是将“策略”的一个实例嵌入到新对象中。因为我们使用私有继承，所以与LSP无关--与基于策略的模板非常相似，其目的不是创建一个大型层次结构来断言层次结构成员之间的任何关系--相反，它只是创建按需创建大量不相关类的能力。|1228353|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

IMO, it's open to argument. Prior to templates, there were a fair number of cases that justified it. Basically, you could use base classes about like you can use policy classes with templates. For example, consider a template like:

<pre><code>template &lt;typename policy1, typename policy2&gt;
class whatever {
 policy1 p1;
 policy2 p2;
public:
 void dosomething() { if (p1.enquire()) p2.dosomething(); }
};
</code></pre>

If you'd rather not use templates for some reason, you can get (some) fairly similar capabilities with multiple inheritance:

<pre><code>class whatever : policy1, policy2 { 
 void dosomething() { if (enquire()) dosomething(); }
</code></pre>

};

In both cases, you're basically embedding an instance of the "policy" into your new object. Since we're using private inheritance, there's no concern with the LSP -- much like with policy-based templates, the intent isn't to create a large hierarchy that asserts anything about relationships between the members of the hierarchy -- rather, it's simply about creating the ability to create a large variety of unrelated classes on demand.

blocks|key|133433|text|我在“现实世界”中使用了多重继承--在我参与编写地图应用程序的工作中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|133434|不幸的是，我不记得确切的例子，我发现令人难以置信的沮丧。|133435|然而，这里有一篇有趣的文章，介绍了要考虑的要点以及要考虑使用的替代模式或解决方案：|133436|http://www.parashift.com/c%2B%2B-faq-lite/multiple-inheritance.html#faq-25.2|offset|length|133437|我喜欢在示例中使用车辆-特别是添加两栖车辆。|133438|entityMap|0|LINK|mutability|MUTABLE|url|http://www.parashift.com/c%2B%2B-faq-lite/multiple-inheritance.html#faq-25.2^0|0|0|0|0|20|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|W|8|@]|9|@$H|X|I|Y|1|Z]]|A|$]]|$1|J|3|K|5|6|7|10|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|M|$N|$5|O|P|Q|A|$R|S]]]]

I have used multiple inheritance in the 'real world' - in a job where I was involved in coding a mapping application.

Unfortunately, I cannot remember the exact example which I find incredibly frustrating.

However, here is an interesting article about points to consider and alternative patterns or solutions to consider using:

<a href="http://www.parashift.com/c++-faq-lite/multiple-inheritance.html#faq-25.2" rel="nofollow noreferrer">http://www.parashift.com/c++-faq-lite/multiple-inheritance.html#faq-25.2</a>

I like the use of vehicles for the examples - particularly adding in the amphibious vehicle.

blocks|key|1228316|text|多重继承肯定有它的位置，它可以非常有用。一般来说，基类应该尽可能是抽象的，这意味着你不应该从基类中创建对象，但没有什么能阻止你继承具体的类。这绝对也是一个优点，你可以利用从基类继承的实现。在iostream上的一个答案上的例子是一个很好的例子。另一个例子可能是对同时也是企业所有者/董事的员工建模，您将其建模为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1228317|public+class+Director
{
+++................
+++double+CalculateDividend();
+++bool+ApproveBudget();
};

public+class+Employee
{
+++................
+++double+CalculateSalary();
};


public+class+WorkingDirector:+Employee,+Director
{
+++..............
};|code-block|syntax|javascript|1228318|现在，WorkingDirector对象可以做雇员和主管都能做的事情，这在现实世界中是完美的。我们甚至不需要重写任何方法实现。|1228319|在许多情况下，通过多重继承支持，设计模式的实现也变得更容易。|1228320|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Multiple inheritance definitely has its place and it can be very useful. As a general guideline a base class should be abstract whenever possible, which means you shouldnt be able to create an object out of it, but nothing stop you from inheriting from concrete class. It is definitely a merit too t hat you can take advantage of the inherited implementation from base class. Example on one of the answer on iostream is a good one. Another example is perhaps to say modelling a employee who is also an owner/director of a business and you will model it as

<pre><code>public class Director
{
 ................
 double CalculateDividend();
 bool ApproveBudget();
};

public class Employee
{
 ................
 double CalculateSalary();
};


public class WorkingDirector: Employee, Director
{
 ..............
};
</code></pre>

Now a WorkingDirector object can do what an Employee and a Director can do, which is a perfect in realworld. We wouldnt even need to overwrite any method implementation. 

In many cases implementing design patterns are also made easier with multiple inheritance support.

blocks|key|132786|text|如果我们有一个类击球手，它有像no+of+run这样的数据成员，那么就没有。我们有另一个类'Bowler‘，它可能有像no.of+wickets，run-per-over，average-wicket等数据成员。对于一个全能的球员，类’all+-All‘将从类’击球手‘和’保龄球‘派生出来。这可以被引用为一个真实的多重继承的例子|type|unstyled|depth|inlineStyleRanges|entityRanges|data|132787|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If we have a class batsman which has data members like no of runs,no. of sixes, no of fours, batting average, run-rate etc. We have another class 'Bowler' which may have data members like no.of wickets taken, runs-per-over, average-wicket etc. For a player who is an all rounder, the class 'All-Rounder' will be derived from both the classes 'Batsman' and &quot;Bowler'.
This can be cited as a real world example of multiple inheritance

Besides textbook examples -- in the real world -- does it ever make sense to use multiple inheritance (where more than one of the base classes are not pure interfaces) in C++?

What are real-world examples of C++ multiple inheritance?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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除了教科书上的例子--在现实世界中--在C++中使用多重继承(其中多个基类不是纯接口)有意义吗？

问C++多重继承的实际例子有哪些？
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回答 7

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