blocks|key|1625826|text|我肯定会去辛格尔顿班。这是在多线程OOP环境中处理“全局”变量的最佳方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1625827|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|$]]

I would definitely go with the Singleton class. It's the best way to handle "global" variables in a multithreaded OOP environment.

blocks|key|1625850|text|如果必须使用全局变量(为什么要使用全局变量？)我推荐你描述的第二种方式。第一种方法是遇到各种命名空间问题的方式。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1625851|entityMap^0|2|1I|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

If you must use a global variable (and why are you using one?) I recommend the second way you described. The first way is the way you can run into all kinds of namespace problems.

blocks|key|1625869|text|首先，尽量避免全局变量。如果您只需要这样做(例如，cin、cout和cerr就是这种情况)，那么第二个方法无疑是最好的(也是更自然的)方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1625870|entityMap^0|P|3|T|4|Y|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

First of all try to avoid global variables as much as you can. If you just need to do it (by example this is the case with <code>cin</code>, <code>cout</code> and <code>cerr</code>) your second method is definitely the best (and more natural) way of doing it.

blocks|key|1980339|text|这取决于眼前的问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1980340|C风格的全局语言具有简单性的优点，不需要Singleton::instance()调用。但是，Singleton::instance()允许您在第一次调用时初始化您的全局状态。|1980341|要获得这两个世界的最佳效果，请使用使用Schwarz计数器方法初始化的C样式全局值。计数器|offset|length|1980342|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikibooks.org/wiki/More_C%252B%252B_Idioms/Nifty_Counter^0|0|0|16|3|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

It depends on the problem at hand.

C-style globals have the advantage of simplicity, no need for Singleton::instance() call. However, Singleton::instance() allows you to initialize your global state on the first call.

To get the best of both worlds use C-style globals initialized using Schwarz Counter method. <a href="http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Nifty_Counter" rel="nofollow noreferrer">http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Nifty_Counter</a>

blocks|key|1625903|text|如果可以缩小“全局变量”的范围(这通常是这样的--有多少变量是真正的全局变量？)然后，您可以在适当的拥有类中使其成为私有静态类成员。如果您的其他类需要查看它(或者不太可能更新它)，请提供get/put访问器。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1625904|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 the scope of your "global variable" can be narrowed down (which is typically the case - how many variables are truly global?) then you can make it a private static class member in the appropriate owning class. If your other classes need to see it (or less likely, update it), provide get/put accessors.

blocks|key|1980412|text|您可以定义一个值对象，它用句柄/正文习语包装单个实现。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1980413|还回顾了Alexandrescu的“现代C%2B%2B设计”，讨论了在MT环境中实现单例的困难以及如何解决这些问题。|1980414|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

You can define a value object that wraps a single implementation with the handle/body idiom.

Also review "Modern C++ Design" by Alexandrescu for discussion about the difficulties of implementing singleton in MT environments and how to go about addressing them.

blocks|key|1980428|text|这个问题可以很容易地用交替法求解。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1980429|C%2B%2B通过其新的操作符::+(称为范围解析运算符)很容易地解决了这个问题。语法如下|offset|length|style|BOLD|1980430|::+variable-name;|code-block|syntax|javascript|1980431|此操作符允许访问vriable的全局版本。|1980432|entityMap^0|0|B|2|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|U|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

This probleam can be solved with an alternatieve method very easily.

C++ resolves this problem very easily by its new operator :: called scope resolution operator. The syntax is as follows

<pre><code>:: variable-name;
</code></pre>

This operator allows access the global version of a vriable.

blocks|key|428472|text|不是踢死马，而是，如前所述，避免全球是最好的解决办法。列举了这里的一些原因。如果一个全局变量是必需的，您可能想考虑提供一个函数来访问它，以避免所谓的“全局初始化失败”。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|428473|entityMap|0|LINK|mutability|MUTABLE|url|http://bytes.com/topic/c/insights/737451-case-against-global-variables^0|U|2|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]]]]

Not to kick a dead horse but, as mentioned, avoiding globals is the best solution. Some reasons are listed <a href="http://bytes.com/topic/c/insights/737451-case-against-global-variables" rel="nofollow noreferrer" title="here">here</a>. If a global variable is a must you might want to consider providing a function to access it from to avoid the so called 'global initialization fiasco'.

blocks|key|1980527|text|人们倾向于使用第二种方法，因为它似乎给了您更好的控制，但在某些情况下可能不太有用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1980528|首先，在我对OOP哲学的理解中，我不认为对象是一堆数据的集合，而是实体，根据这些数据，您可以表示现实世界的问题。因此，我不认为有一个类来存储随机数据是一个好主意。尤其是当数据成员在很大程度上是无关的时候。|1980529|第二，如果你想有一个中央控制，例如。有一个互斥体来访问所有的数据成员，对于不相关的数据成员来说，这并不是很好的结果。您将不必要地阻塞许多线程，而它们想要的数据并不完全是当前受锁保护的数据。|1980530|因此，这似乎很奇怪，但我更喜欢第一种方法。|1980531|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

One tends to prefer the second method, because it seems to give you a better control but it may not turn out very useful in some scenarios. 

First, In my understanding of philosophy of OOP, I do not consider objects as collections of bunch of data, but entities in terms of which, you can represent real world problems. So I do not consider it a good idea to to have a class to store random data. Especially when the data members are largely unrelated.

Second, If you are thinking of having a central control eg. having a single mutex to access all the data members, this is not going to work out very well for unrelated data members. You are going to block a lot of threads unnecessarily while the data they want is not exactly the one which is being currently protected by the lock.

So it may seem strange, but I would prefer the first method.

In a C++ multi-threaded application with many classes, i am trying to find out what are the methods to define a global variable

<ol>
<li>C style, define it as global in any one source file, define it as extern in a header which is included in the classes that access this variable.</li>
<li>Write a Singleton class, which contains these global variables and exposes set/get methods to write to the variable. </li>
</ol>

By second method one can control multi-threaded access via locks in a centralized manner rather than the first approach. 

Are there more and better ways?

global variables 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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在一个具有许多类的C++多线程应用程序中，我试图找出定义全局变量的方法。C样式，在任何一个源文件中将其定义为全局的，在访问此变量的类中将其定义为包含在头中的extern。编写Singleton类，该类包含这些全局变量，并公开要写入变量的set/get方法。通过第二种方法，可以通过集中方式而不是第一种方法通过锁来控制多线...

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