blocks|key|1644562|text|本质上，它是代码中的一个位置，允许您点击模块以提供不同的行为或在发生事情时做出反应。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1644563|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|$]]

Essentially it's a place in code that allows you to tap in to a module to either provide different behavior or to react when something happens.

blocks|key|1644874|text|在一般意义上，“钩子”是允许程序员查看和/或交互和/或更改系统/程序中已经发生的事情的东西。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1644875|例如，Drupal+CMS为开发人员提供了钩子，允许他们在创建“内容节点”后执行其他操作。如果开发人员没有实现钩子，那么节点是按照正常方式创建的。如果开发人员实现了钩子，他们可以在创建节点时运行一些额外的代码。这段代码可以做任何事情，包括回滚和/或更改原始操作。它还可以做一些与节点创建完全无关的事情。|1644876|回调可以被认为是一种特定的钩子。通过在系统中实现回调功能，该系统允许您在操作完成后调用一些额外的代码。然而，挂钩(作为一个通用术语)并不局限于回调。|1644877|另一个例子。有时，Web开发人员会将元素上的类名和/或ID称为挂钩。这是因为通过将ID/类名放在元素上，他们就可以使用Javascript修改该元素，或者将其“挂钩”到页面文档中。(这是延伸的意思，但它是常用的，值得一提的是)|1644878|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|$]]

In a generic sense, a "hook" is something that will let you, a programmer, view and/or interact with and/or change something that's already going on in a system/program.

For example, the Drupal CMS provides developers with hooks that let them take additional action after a "content node" is created. If a developer doesn't implement a hook, the node is created per normal. If a developer implements a hook, they can have some additional code run whenever a node is created. This code could do anything, including rolling back and/or altering the original action. It could also do something unrelated to the node creation entirely. 

A callback could be thought of as a specific kind of hook. By implementing callback functionality into a system, that system is letting you call some additional code after an action has completed. However, hooking (as a generic term) is not limited to callbacks.

Another example. Sometimes Web Developers will refer to class names and/or IDs on elements as hooks. That's because by placing the ID/class name on an element, they can then use Javascript to modify that element, or "hook in" to the page document. (this is stretching the meaning, but it is commonly used and worth mentioning)

blocks|key|1645369|text|简单地说：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1645370|钩子是在现有代码之前、之后或代替现有代码执行自定义代码(函数)的一种方法。例如，可以将函数写入到登录进程中，以便在继续到正常登录进程之前执行验证码函数。|1645371|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|$]]

Simple said:

A hook is a means of executing custom code (function) either before, after, or instead of existing code. For example, a function may be written to "hook" into the login process in order to execute a Captcha function before continuing on to the normal login process.

blocks|key|1430372|text|钩子是一类允许基代码调用扩展代码的函数。这在核心开发人员希望在不公开代码的情况下提供可扩展性的情况下很有用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1430373|钩子的一种用法是在视频游戏mod开发中。游戏可能不允许mod开发人员扩展基本功能，但核心mod库开发人员可以添加钩子。有了这些钩子，独立开发人员可以在任何所需的事件上调用他们的自定义代码，例如游戏加载、库存更新、实体交互等。|1430374|一种常见的实现方法是给函数一个空的回调列表，然后公开扩展回调列表的能力。基代码将始终在相同和适当的时间调用函数，但是，如果回调列表为空，则函数什么也不做。这是设计好的。|1430375|然后，第三方有机会编写额外的代码并将它们的新回调添加到钩子的回调列表中。通过引用可用的钩子，它们以最小的风险扩展了基本系统的功能。|1430376|钩子不允许开发人员做任何其他结构和接口不能做的事情。它们是在考虑任务和用户(第三方开发人员)的情况下做出的选择。|1430377|需要说明的是:钩子允许扩展，并且可以使用回调实现。回调通常只是一个函数指针；函数的计算地址。在其他答案/评论中似乎存在混淆。|1430378|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|P|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|Q|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|R|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|S|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|M|$]]

Hooks are a category of function that allows base code to call extension code. This can be useful in situations in which a core developer wants to offer extensibility without exposing their code.

One usage of hooks is in video game mod development. A game may not allow mod developers to extend base functionality, but hooks can be added by core mod library developers. With these hooks, independent developers can have their custom code called upon any desired event, such as game loading, inventory updates, entity interactions, etc.

A common method of implementation is to give a function an empty list of callbacks, then expose the ability to extend the list of callbacks. The base code will always call the function at the same and proper time but, with an empty callback list, the function does nothing. This is by design.

A third party, then, has the opportunity to write additional code and add their new callback to the hook's callback list. With nothing more than a reference of available hooks, they have extended functionality at minimal risk to the base system.

Hooks don't allow developers to do anything that can't be done with other structures and interfaces. They are a choice to be made with consideration to the task and users (third-party developers).

For clarification: a hook allows the extension and may be implemented using callbacks. Callbacks are generally nothing more than a function pointer; the computed address of a function. There appears to be confusion in other answers/comments.

blocks|key|1644616|text|编程中的钩子(+Hooking+)是一种技术，它使用所谓的钩子来创建一系列过程作为事件处理程序。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1644617|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Hooking^0|8|7|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]]]]

<a href="http://en.wikipedia.org/wiki/Hooking" rel="noreferrer">Hooking</a> in programming is a technique employing so-called hooks to make a chain of procedures as an event handler.

blocks|key|1645185|text|钩子表示代码中的一个地方，在那里你可以分派一个特定类型的事件，如果这个事件以前是用一个合适的回调函数注册的，那么它将由这个注册的函数来处理，否则什么都不会发生。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1645186|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|$]]

Hook denotes a place in the code where you dispatch an event of certain type, and if this event was registered before with a proper function to call back, then it would be handled by this registered function, otherwise nothing happens.

blocks|key|1644660|text|当遇到某些条件时，可以执行钩子。例如，一些变量的变化，或者一些动作被调用，或者一些事件发生。钩子可以进入这个过程并改变事物或对改变做出反应。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1644661|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|$]]

hooks can be executed when some condition is encountered. e.g. some variable changes or some action is called or some event happens. hooks can enter in the process and change things or react upon changes.

blocks|key|1429845|text|挂钩通常指的是Win32+message+hooking或Linux/OSX的等价物，但更普遍的是，挂钩只是通知另一个对象/窗口/程序/等，当指定的操作发生时，您希望得到通知。例如:让系统上的所有窗口在它们即将关闭时通知您。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1429846|作为一般规则，挂钩是有点危险的，因为在不了解它如何影响系统的情况下这样做可能会导致不稳定或至少是意外的行为。在某些情况下，它也是非常有用的。例如：FRAPS使用它来确定应该在哪个窗口上显示它的FPS计数器。|1429847|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/ms997537.aspx|1|http://www.fraps.com/^0|7|L|0|0|21|5|1|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]]|C|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|F|3|-4|5|6|7|X|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|O]]]]

Oftentimes hooking refers to <a href="http://msdn.microsoft.com/en-us/library/ms997537.aspx" rel="nofollow noreferrer">Win32 message hooking</a> or the Linux/OSX equivalents, but more generically hooking is simply notifying another object/window/program/etc that you want to be notified when a specified action happens. For instance: Having all windows on the system notify you as they are about to close.

As a general rule, hooking is somewhat hazardous since doing it without understanding how it affects the system can lead to instability or at the very leas unexpected behaviour. It can also be VERY useful in certain circumstances, thought. For instance: <a href="http://www.fraps.com/" rel="nofollow noreferrer">FRAPS</a> uses it to determine which windows it should show it's FPS counter on.

blocks|key|1430019|text|钩子链是一组函数，每个函数调用下一个函数。钩子链的重要之处在于，程序员可以在运行时将另一个函数添加到钩子链中。要做到这一点，一种方法是查找保存链中第一个函数地址的已知位置。然后保存该函数指针的值，并用要插入钩链的函数的地址覆盖初始地址处的值。然后调用该函数，执行其业务，并调用链中的下一个函数(除非您另有决定)。当然，还有许多其他方法可以创建钩子链，从直接写入内存到使用Ruby或Python等语言的元编程工具。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1430020|钩子链的一个示例是MS+Windows应用程序处理消息的方式。处理链中的每个函数要么处理消息，要么将消息发送给链中的下一个函数。|1430021|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|$]]

A chain of hooks is a set of functions in which each function calls the next. What is significant about a chain of hooks is that a programmer can add another function to the chain at run time. One way to do this is to look for a known location where the address of the first function in a chain is kept. You then save the value of that function pointer and overwrite the value at the initial address with the address of the function you wish to insert into the hook chain. The function then gets called, does its business and calls the next function in the chain (unless you decide otherwise). Naturally, there are a number of other ways to create a chain of hooks, from writing directly to memory to using the metaprogramming facilities of languages like Ruby or Python. 

An example of a chain of hooks is the way that an MS Windows application processes messages. Each function in the processing chain either processes a message or sends it to the next function in the chain.

blocks|key|1430122|text|在Drupal内容管理系统中，“挂钩”有相对特定的含义。当内部事件发生时(例如，内容创建或用户登录)，模块可以通过实现特殊的“挂钩”函数来响应事件。这是通过命名约定完成的--例如，用户登录事件的your-plugin-name_+User+_+Login+()。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1430123|由于这种约定，底层事件被称为“钩子”，并且在Drupal文档中以"hook_user_login“和"hook_user_authenticate()”这样的名称出现。|1430124|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|$]]

In the Drupal content management system, 'hook' has a relatively specific meaning. When an internal event occurs (like content creation or user login, for example), modules can respond to the event by implementing a special "hook" function. This is done via naming convention -- [your-plugin-name]_user_login() for the User Login event, for example.

Because of this convention, the underlying events are referred to as "hooks" and appear with names like "hook_user_login" and "hook_user_authenticate()" in Drupal's API documentation.

blocks|key|1645088|text|简而言之，您可以将MessageBox等API调用的代码更改为执行由您编辑的不同函数的位置(全局将在系统范围内工作，本地将在进程范围内工作)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1645089|entityMap^0|9|A|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|$]]

In VERY short, you can change the code of an API call such as <code>MessageBox</code> to where it does a different function edited by you (globally will work system wide, locally will work process wide).

blocks|key|1430534|text|有很多答案，但没有示例，所以添加一个虚拟答案:下面的complicated_func提供了两个钩子来修改它的行为|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1430535|from+typing+import+List,+Callable


def+complicated_func(
++++lst:+List[int],+hook_modify_element:+Callable[[int],+int],+hook_if_negative=None
)+->+int:
++++res+=+sum(hook_modify_element(x)+for+x+in+lst)
++++if+res+<+0+and+hook_if_negative+is+not+None:
++++++++print("Returning+negative+hook")
++++++++return+hook_if_negative
++++return+res


def+my_hook_func(x:+int)+->+int:
++++return+x+*+2


if+__name__+==+"__main__":
++++res+=+complicated_func(
++++++++lst=[1,+2,+-10,+4],
++++++++hook_modify_element=my_hook_func,
++++++++hook_if_negative=0,
++++)
++++print(res)|code-block|syntax|javascript|1430536|entityMap^0|Q|G|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Many answers, but no examples, so adding a dummy one: the following <code>complicated_func</code> offers two hooks to modify its behavior
<pre><code>from typing import List, Callable


def complicated_func(
 lst: List[int], hook_modify_element: Callable[[int], int], hook_if_negative=None
) -&gt; int:
 res = sum(hook_modify_element(x) for x in lst)
 if res &lt; 0 and hook_if_negative is not None:
 print(&quot;Returning negative hook&quot;)
 return hook_if_negative
 return res


def my_hook_func(x: int) -&gt; int:
 return x * 2


if __name__ == &quot;__main__&quot;:
 res = complicated_func(
 lst=[1, 2, -10, 4],
 hook_modify_element=my_hook_func,
 hook_if_negative=0,
 )
 print(res)
</code></pre>

blocks|key|1430577|text|一个函数，它允许你提供另一个函数，而不仅仅是一个值作为参数，本质上是扩展它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1430578|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|$]]

A function that allows you to supply another function rather than merely a value as an argument, in essence extending it.

I recently heard the term "hook" while talking to some people about a program I was writing. I'm unsure exactly what this term implies although I inferred from the conversation that a hook is a type of function. I searched for a definition but was unable to find a good answer. Would someone be able to give me an idea of what this term generally means and perhaps a small example to illustrate the definition?

What is meant by the term "hook" in programming?

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最近，当我和一些人谈论我正在编写的一个程序时，我听到了“挂钩”这个词。我不确定这个术语到底意味着什么，尽管我从对话中推断出钩子是一种函数。我寻找了一个定义，但找不到一个好的答案。谁能给我一个概念，这个术语通常是什么意思，也许可以举一个小例子来说明这个定义？

问在编程中，术语“钩子”是什么意思？
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问在编程中，术语“钩子”是什么意思？EN

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问在编程中，术语“钩子”是什么意思？
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