blocks|key|1672576|text|C%2B%2B11解决方案|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1672577|在C%2B%2B11中，您可以通过在定义中使用final关键字来密封类，如下所示：|offset|length|style|CODE|1672578|class+A+final++//note+final+keyword+is+used+after+the+class+name
{
+++//...
};

class+B+:+public+A++//error+-+because+class+A+is+marked+final+(sealed).
{+++++++++++++++++++//++++++++so+A+cannot+be+derived+from.
+++//...
};|code-block|syntax|javascript|1672579|要了解final的其他用法，请参阅我的答案：|1672580|1672581|What+is+the+purpose+of+the+"final"+keyword+in+C%2B%2B11+for+functions?|unordered-list-item|1672582|1672583|1672584|C%2B%2B03解决方案|1672585|Bjarne+Stroustrup's+code：我能阻止人们从我的类派生吗？|BOLD|1672586|class+Usable;
class+Usable_lock+{
++++friend+class+Usable;
private:
++++Usable_lock()+{}
++++Usable_lock(const+Usable_lock&)+{}
};

class+Usable+:+public+virtual+Usable_lock+{
public:
++++Usable();
++++Usable(char*);
};
Usable+a;

class+DD+:+public+Usable+{+};

DD+dd;++//+error:+DD::DD()+cannot+access
++++++++//+Usable_lock::Usable_lock():+private++member|1672587|1672588|Generic_lock|1672589|因此，我们可以利用模板使Usable_lock泛型到足以密封任何类：|1672590|template<class+T>
class++Generic_lock+
{
++++friend+T;
++++Generic_lock()+{}+++++++++++++++++++++//private
++++Generic_lock(const+Generic_lock&)+{}++//private
};

class+Usable+:+public+virtual+Generic_lock<Usable>
{
public:
++++Usable()+{}
};

Usable+a;+//Okay
class+DD+:+public+Usable+{+};

DD+dd;+//Not+okay!|1672591|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/8824587/purpose-of-the-final-keyword|1|http://www.stroustrup.com/bs_faq2.html#no-derivation^0|0|J|5|0|0|0|0|0|1U|0|0|0|0|0|P|E|0|O|1|0|0|0|0|C|B|0|0^^$0|@$1|2|3|4|5|6|7|1I|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1J|8|@$D|1K|E|1L|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|1M|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|1N|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]|$1|P|3|Q|5|R|7|1P|8|@]|9|@$D|1Q|E|1R|1|1S]]|A|$]]|$1|S|3|-4|5|6|7|1T|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1U|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1V|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1W|8|@$D|1X|E|1Y|F|Y]]|9|@$D|1Z|E|20|1|21]]|A|$]]|$1|Z|3|10|5|J|7|22|8|@]|9|@]|A|$K|L]]|$1|11|3|-4|5|6|7|23|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|24|8|@]|9|@]|A|$]]|$1|14|3|15|5|6|7|25|8|@$D|26|E|27|F|G]]|9|@]|A|$]]|$1|16|3|17|5|J|7|28|8|@]|9|@]|A|$K|L]]|$1|18|3|-4|5|6|7|29|8|@]|9|@]|A|$]]]|19|$1A|$5|1B|1C|1D|A|$1E|1F]]|1G|$5|1B|1C|1D|A|$1E|1H]]]]

<h2>C++11 solution</h2>
In C++11, you can seal a class by using <code>final</code> keyword in the definition as:
<pre><code>class A final //note final keyword is used after the class name
{
 //...
};

class B : public A //error - because class A is marked final (sealed).
{ // so A cannot be derived from.
 //...
};
</code></pre>
To know the other uses of final, see my answer here:
<ul>
<li><a href="https://stackoverflow.com/questions/8824587/purpose-of-the-final-keyword">What is the purpose of the &quot;final&quot; keyword in C++11 for functions?</a></li>
</ul>
<hr />
<h2>C++03 solution</h2>
<a href="http://www.stroustrup.com/bs_faq2.html#no-derivation" rel="noreferrer">Bjarne Stroustrup's code</a> : Can I stop people deriving from my class?
<pre><code>class Usable;
class Usable_lock {
 friend class Usable;
private:
 Usable_lock() {}
 Usable_lock(const Usable_lock&amp;) {}
};

class Usable : public virtual Usable_lock {
public:
 Usable();
 Usable(char*);
};
Usable a;

class DD : public Usable { };

DD dd; // error: DD::DD() cannot access
 // Usable_lock::Usable_lock(): private member
</code></pre>
<hr />
<h3>Generic_lock</h3>
So we can make use of template to make the <code>Usable_lock</code> generic enough to seal any class:
<pre><code>template&lt;class T&gt;
class Generic_lock 
{
 friend T;
 Generic_lock() {} //private
 Generic_lock(const Generic_lock&amp;) {} //private
};

class Usable : public virtual Generic_lock&lt;Usable&gt;
{
public:
 Usable() {}
};

Usable a; //Okay
class DD : public Usable { };

DD dd; //Not okay!
</code></pre>

blocks|key|645354|text|你不能。C%2B%2B不是Java或C#。而且也没有任何意义，永远不会。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|645355|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|$]]

You cannot. C++ is not Java or C#. And also there is no point, ever, IMHO.

blocks|key|1675054|text|有两种方法，简单、便宜和正确的方法。@Naveen和@Nawaz的两个答案处理了正确的答案，即需要为您实际想要密封的每个类手动创建一个密封器类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1675055|在adobe库中使用的不是最简单的方法是使用模板化的类。问题是您不能将模板参数声明为朋友，这意味着您将不得不从private切换到安全性较低的protected|offset|length|style|CODE|1675056|template+<typename+T>
class+sealer+{
protected:+sealer()+{}
};
class+sealed+:+virtual+sealer<sealed>+{};|code-block|syntax|javascript|1675057|你可以通过一个宏来实现自动化(我不记得Adobe代码中宏的确切风格了)：|1675058|#define+seal(+x+)+virtual+sealer<x>
class+sealed+:+seal(sealed)+
{};|1675059|现在，这将捕获那些错误地试图继承而不知道他们不应该继承的人：|1675060|class+derived+:+sealed+{};
int+main()+{
+++derived+d;++//+sealer<T>::sealer()+is+protected+within+this+context
}|1675061|但它不会阻止那些真正想要派生的人，因为他们可以通过自己从模板派生来获得对构造函数的访问：|1675062|class+derived+:+sealed,+sealer<sealed>+{};
int+main()+{
+++derived+d;
};|1675063|我不确定这是否会在C%2B%2B0x中改变，我想我记得有一些关于是否允许类模板与它的一个参数成为好友的讨论，但粗略地浏览一下草案，我真的不能确定。如果这是允许的，那么这将是一个很好的通用解决方案：|1675064|template+<typename+T>
class+sealer+{
+++sealer()+{}
+++friend+class+T;+//+Incorrect+in+C%2B%2B03
};|1675065|entityMap^0|0|1J|7|1Z|9|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|15|8|@$D|16|E|17|F|G]|$D|18|E|19|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|1A|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|1B|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|1C|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|1D|8|@]|9|@]|A|$]]|$1|S|3|T|5|J|7|1E|8|@]|9|@]|A|$K|L]]|$1|U|3|V|5|6|7|1F|8|@]|9|@]|A|$]]|$1|W|3|X|5|J|7|1G|8|@]|9|@]|A|$K|L]]|$1|Y|3|Z|5|6|7|1H|8|@]|9|@]|A|$]]|$1|10|3|11|5|J|7|1I|8|@]|9|@]|A|$K|L]]|$1|12|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]]|13|$]]

There are two ways, the simple cheap, and the correct one. The two answers by @Naveen and @Nawaz deal with the correct one, that requires manual creation of a sealer class for each class that you actually want to seal.

The not fool-proof way, which is used in the adobe libraries is using a templated class for that. The problem is that you cannot declare the template argument as a friend, and that means that you will have to switch from <code>private</code> to the less safe <code>protected</code>:

<pre><code>template &lt;typename T&gt;
class sealer {
protected: sealer() {}
};
class sealed : virtual sealer&lt;sealed&gt; {};
</code></pre>

And you can automate it with a macro (I don't remember the exact flavor of the macro in Adobe's code):

<pre><code>#define seal( x ) virtual sealer&lt;x&gt;
class sealed : seal(sealed) 
{};
</code></pre>

Now this will catch people that mistakenly try to inherit without knowing that they shouldn't:

<pre><code>class derived : sealed {};
int main() {
 derived d; // sealer&lt;T&gt;::sealer() is protected within this context
}
</code></pre>

But it will not inhibit people that really want to from deriving, as they can gain access to the constructor by deriving from the template themselves:

<pre><code>class derived : sealed, sealer&lt;sealed&gt; {};
int main() {
 derived d;
};
</code></pre>

I am not sure whether this will change in C++0x, I think I recall some discussions on whether a class template would be allowed to befriend one of it's arguments, but in a cursory search through the draft I cannot really tell. If that was allowed then this would be a fine generic solution:

<pre><code>template &lt;typename T&gt;
class sealer {
 sealer() {}
 friend class T; // Incorrect in C++03
};
</code></pre>

blocks|key|2712433|text|C%2B%2B11添加了防止继承类或简单地防止重写派生类中的方法的功能。这是通过特殊标识符final完成的。例如：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2712434|class+Base+final+{+};

class+Derived1+:+Base+{+};+//+ill-formed+because+the+class+Base+has+been+marked+final|code-block|syntax|javascript|2712435|或|2712436|class+Base+{
++++virtual+void+f()+final;
};

class+Derived+:+Base+{
++++void+f();+//+ill-formed+because+the+virtual+function+Base::f+has+been+marked+final|2712437|请注意，final不是语言关键字。从技术上讲，它是一个标识符；只有在这些特定的上下文中使用时，它才具有特殊的意义。在任何其他位置，它都可以是有效的标识符。|2712438|entityMap^0|15|5|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|Y|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

C++11 adds the ability to prevent inheriting from classes or simply preventing overriding methods in derived classes. This is done with the special identifier <code>final</code>. For example:

<pre><code>class Base final { };

class Derived1 : Base { }; // ill-formed because the class Base has been marked final
</code></pre>

or

<pre><code>class Base {
 virtual void f() final;
};

class Derived : Base {
 void f(); // ill-formed because the virtual function Base::f has been marked final
</code></pre>

Note that final is not a language keyword. It is technically an identifier; it only gains special meaning when used in those specific contexts. In any other location, it can be a valid identifier.

blocks|key|4314847|text|下面的代码显示了如何在C%2B%2B/CLI中定义密封类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4314848|class+A+sealed
{
++++//here+goes+the+class+code
};

class+B+:+public+A
{
};|code-block|syntax|javascript|4314849|现在B:不能从A继承，因为它已被声明为“sealed”。此外，有关sealed关键字的详细说明可在此处http://msdn.microsoft.com/en-us/library/0w2w91tf.aspx中找到|offset|length|4314850|更新:添加了C%2B%2B/CLI，其他答案也显示了使用final关键字实现相同功能的最新C%2B%2B11方法。|style|CODE|4314851|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/0w2w91tf.aspx^0|0|0|1F|1H|0|0|O|5|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@$I|Z|J|10|1|11]]|A|$]]|$1|K|3|L|5|6|7|12|8|@$I|13|J|14|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

The following code shows how to define a sealed class in C++/CLI.

<pre><code>class A sealed
{
 //here goes the class code
};

class B : public A
{
};
</code></pre>

Now B : cannot inherit from A as it has been declared as 'sealed'. Also a detailed explanation about sealed keyword can be found here <a href="http://msdn.microsoft.com/en-us/library/0w2w91tf.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/0w2w91tf.aspx</a>

Update: Added C++/CLI , also other answers have shown the latest C++11 way of achieving the same using <code>final</code> keyword.

blocks|key|1675115|text|基于Bjarne+Stroustrup的http://www.stroustrup.com/bs_faq2.html#no-derivation常见问题解答，只做了很小的修改，没有使用朋友关键字：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1675116|//+SEALED+CLASS+DEFINITIONS
class+Usable_lock+{
protected:
++++Usable_lock()+{}
++++Usable_lock(const+Usable_lock&)+{}
};
#define+sealed_class+private+virtual+Usable_lock

//+SEALED+CLASS+USAGE+EXMAPLES
class+UsableLast+:+sealed_class+{
public:
++++UsableLast(){}
++++UsableLast(char*){}
};
class+DD+:+public+UsableLast+{};

//+TEST+CODE
template+<class+T>+T+createInstance()+{
++++return+T();
}
int+main()
{
++++createInstance<UsableLast>();
//++createInstance<DD>();
++++return+0;
}|code-block|syntax|javascript|1675117|entityMap|0|LINK|mutability|MUTABLE|url|http://www.stroustrup.com/bs_faq2.html#no-derivation^0|K|1G|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Based on Bjarne Stroustrup's <a href="http://www.stroustrup.com/bs_faq2.html#no-derivation" rel="nofollow">http://www.stroustrup.com/bs_faq2.html#no-derivation</a> FAQ
with small modification without friend keyword usage:

<pre><code>// SEALED CLASS DEFINITIONS
class Usable_lock {
protected:
 Usable_lock() {}
 Usable_lock(const Usable_lock&amp;) {}
};
#define sealed_class private virtual Usable_lock

// SEALED CLASS USAGE EXMAPLES
class UsableLast : sealed_class {
public:
 UsableLast(){}
 UsableLast(char*){}
};
class DD : public UsableLast {};

// TEST CODE
template &lt;class T&gt; T createInstance() {
 return T();
}
int main()
{
 createInstance&lt;UsableLast&gt;();
// createInstance&lt;DD&gt;();
 return 0;
}
</code></pre>

How to stop the class to be inherited by other class.

How to define sealed class in C++?

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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问如何在C++中定义密封类？
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问如何在C++中定义密封类？EN