blocks|key|186852|text|尽管定义在函数作用域内的变量不能从外部访问，但这并不意味着在该函数完成后就不能使用它们的值。PHP有一个众所周知的static关键字，它在面向对象的PHP中被广泛用于定义静态方法和属性，但是应该记住，static也可以在函数中用来定义静态变量。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|186853|什么是‘静态变量’？|BOLD|186854|静态变量与函数作用域中定义的普通变量的不同之处在于，当程序执行离开此作用域时，静态变量不会散开值。让我们考虑以下使用静态变量的示例：|186855|function+countSheep($num)+{
+static+$counter+=+0;
+$counter+%2B=+$num;
+echo+"$counter+sheep+jumped+over+fence";
}

countSheep(1);
countSheep(2);
countSheep(3);|code-block|syntax|javascript|186856|结果：|186857|1+sheep+jumped+over+fence
3+sheep+jumped+over+fence
6+sheep+jumped+over+fence|186858|如果我们定义了不带static的$counter，那么每次回显的值将与传递给函数的$num参数相同。使用static可以构建这个简单的计数器，而不需要额外的解决方法。|186859|静态变量用例|186860|186861|用于在后续的函数调用之间存储值。|ordered-list-item|186862|用于在无法(或没有目的)将值作为参数传递时在递归调用之间存储值。|186863|用于缓存值，这通常更好地检索一次。例如，读取服务器上的不可变文件的结果。|186864|186865|技巧|186866|静态变量仅存在于局部函数范围中。不能在定义它的函数之外访问它。因此，您可以确定它将保持其值不变，直到下一次调用该函数。|186867|静态变量只能定义为标量或标量表达式(从PHP+5.6开始)。将其他值赋给它不可避免地会导致失败，至少在撰写本文的时候是这样。不过，您可以在代码的下一行执行此操作：|186868|function+countSheep($num)+{
++static+$counter+=+0;
++$counter+%2B=+sqrt($num);//imagine+we+need+to+take+root+of+our+sheep+each+time
++echo+"$counter+sheep+jumped+over+fence";
}|186869|186870|2+sheep+jumped+over+fence
5+sheep+jumped+over+fence
9+sheep+jumped+over+fence|186871|静态函数在同一类的对象的方法之间是某种“共享”的。通过查看以下示例，很容易理解：|186872|class+SomeClass+{
++public+function+foo()+{
++++static+$x+=+0;
++++echo+%2B%2B$x;
++}
}

$object1+=+new+SomeClass;
$object2+=+new+SomeClass;

$object1->foo();+//+1
$object2->foo();+//+2+oops,+$object2+uses+the+same+static+$x+as+$object1
$object1->foo();+//+3+now+$object1+increments+$x
$object2->foo();+//+4+and+now+his+twin+brother|186873|这只适用于同一类的对象。如果对象来自不同的类(甚至相互扩展)，则静态变量的行为将如预期的那样。|186874|是静态变量，这是在函数调用之间保持值的唯一方法--|186875|在函数调用之间保持值的另一种方法是使用闭包。闭包是在PHP+5.3中引入的。换句话说，它们允许您将对某个函数范围内的某些变量集的访问限制为另一个匿名函数，而这将是访问这些变量的唯一方法。在闭包变量中可以模仿(或多或少成功地)+OOP概念，比如结构化编程中的“类常量”(如果它们是通过值传递的闭包)或“私有属性”(如果通过引用传递)。|186876|后者实际上允许使用闭包而不是静态变量。使用什么总是由开发人员决定，但应该提到的是，静态变量在处理递归时绝对有用，值得开发人员注意。|186877|entityMap^0|1L|6|2S|6|0|0|A|0|0|0|0|0|9|6|G|8|15|4|1G|6|0|0|6|0|0|0|0|0|0|0|2|0|0|0|0|0|0|0|0|0|0|P|0|0|0^^$0|@$1|2|3|4|5|6|7|1V|8|@$9|1W|A|1X|B|C]|$9|1Y|A|1Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|20|8|@$9|21|A|22|B|H]]|D|@]|E|$]]|$1|I|3|J|5|6|7|23|8|@]|D|@]|E|$]]|$1|K|3|L|5|M|7|24|8|@]|D|@]|E|$N|O]]|$1|P|3|Q|5|6|7|25|8|@]|D|@]|E|$]]|$1|R|3|S|5|M|7|26|8|@]|D|@]|E|$N|O]]|$1|T|3|U|5|6|7|27|8|@$9|28|A|29|B|C]|$9|2A|A|2B|B|C]|$9|2C|A|2D|B|C]|$9|2E|A|2F|B|C]]|D|@]|E|$]]|$1|V|3|W|5|6|7|2G|8|@$9|2H|A|2I|B|H]]|D|@]|E|$]]|$1|X|3|-4|5|6|7|2J|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|10|7|2K|8|@]|D|@]|E|$]]|$1|11|3|12|5|10|7|2L|8|@]|D|@]|E|$]]|$1|13|3|14|5|10|7|2M|8|@]|D|@]|E|$]]|$1|15|3|-4|5|6|7|2N|8|@]|D|@]|E|$]]|$1|16|3|17|5|6|7|2O|8|@$9|2P|A|2Q|B|H]]|D|@]|E|$]]|$1|18|3|19|5|6|7|2R|8|@]|D|@]|E|$]]|$1|1A|3|1B|5|6|7|2S|8|@]|D|@]|E|$]]|$1|1C|3|1D|5|M|7|2T|8|@]|D|@]|E|$N|O]]|$1|1E|3|Q|5|6|7|2U|8|@]|D|@]|E|$]]|$1|1F|3|1G|5|M|7|2V|8|@]|D|@]|E|$N|O]]|$1|1H|3|1I|5|6|7|2W|8|@]|D|@]|E|$]]|$1|1J|3|1K|5|M|7|2X|8|@]|D|@]|E|$N|O]]|$1|1L|3|1M|5|6|7|2Y|8|@]|D|@]|E|$]]|$1|1N|3|1O|5|6|7|2Z|8|@$9|30|A|31|B|H]]|D|@]|E|$]]|$1|1P|3|1Q|5|6|7|32|8|@]|D|@]|E|$]]|$1|1R|3|1S|5|6|7|33|8|@]|D|@]|E|$]]|$1|1T|3|-4|5|6|7|34|8|@]|D|@]|E|$]]]|1U|$]]

Although variables defined inside of a function's scope can not be accessed from the outside that does not mean you can not use their values after that function completes. PHP has a well known <code>static</code> keyword that is widely used in object-oriented PHP for defining static methods and properties but one should keep in mind that <code>static</code> may also be used inside functions to define static variables.

<h1>What is it 'static variable'?</h1>

Static variable differs from ordinary variable defined in function's scope in case that it does not loose value when program execution leaves this scope. Let's consider the following example of using static variables:

<pre><code>function countSheep($num) {
 static $counter = 0;
 $counter += $num;
 echo "$counter sheep jumped over fence";
}

countSheep(1);
countSheep(2);
countSheep(3);
</code></pre>

Result:

<pre><code>1 sheep jumped over fence
3 sheep jumped over fence
6 sheep jumped over fence
</code></pre>

If we'd defined <code>$counter</code> without <code>static</code> then each time echoed value would be the same as <code>$num</code> parameter passed to the function. Using <code>static</code> allows to build this simple counter without additional workaround.

<h1>Static variables use-cases</h1>

<ol>
<li>To store values between consequent calls to function.</li>
<li>To store values between recursive calls when there is no way (or no
purpose) to pass them as params.</li>
<li>To cache value which is normally better to retrieve once. For
example, result of reading immutable file on server.</li>
</ol>

<h1>Tricks</h1>

Static variable exists only in a local function scope. It can not be
 accessed outside of the function it has been defined in. So you may 
 be sure that it will keep its value unchanged until the next call to
 that function.

Static variable may only be defined as a scalar or as a scalar 
 expression (since PHP 5.6). Assigning other values to it inevitably 
 leads to a failure at least at the moment this article was written.
Nevertheless you are able to do so just on the next line of your code:

<pre><code>function countSheep($num) {
 static $counter = 0;
 $counter += sqrt($num);//imagine we need to take root of our sheep each time
 echo "$counter sheep jumped over fence";
}
</code></pre>

Result:

<pre><code>2 sheep jumped over fence
5 sheep jumped over fence
9 sheep jumped over fence
</code></pre>

Static function is kinda 'shared' between methods of objects of the
 same class. It is easy to understand by viewing the following example:

<pre><code>class SomeClass {
 public function foo() {
 static $x = 0;
 echo ++$x;
 }
}

$object1 = new SomeClass;
$object2 = new SomeClass;

$object1-&gt;foo(); // 1
$object2-&gt;foo(); // 2 oops, $object2 uses the same static $x as $object1
$object1-&gt;foo(); // 3 now $object1 increments $x
$object2-&gt;foo(); // 4 and now his twin brother
</code></pre>

This only works with objects of the same class. If objects are from different classes (even extending one another) behavior of static vars will be as expected.

<h1>Is static variable the only way to keep values between calls to a function?</h1>

Another way to keep values between function calls is to use closures. Closures were introduced in PHP 5.3. In two words they allow you to limit access to some set of variables within a function scope to another anonymous function that will be the only way to access them. Being in closure variables may imitate (more or less successfully) OOP concepts like 'class constants' (if they were passed in closure by value) or 'private properties' (if passed by reference) in structured programming.

The latter actually allows to use closures instead of static variables. What to use is always up to developer to decide but it should be mentioned that static variables are definitely useful when working with recursions and deserve to be noticed by devs.

blocks|key|3016811|text|我不会发布这个问题的完整答案，因为现有的和PHP+manual已经很好地解释了大部分问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3016812|但是遗漏的一个主题是superglobals，包括常用的$_POST、$_GET、$_SESSION等。这些变量是在任何范围内始终可用的数组，没有global声明。|style|CODE|3016813|例如，此函数将打印运行PHP脚本的用户名。该变量对函数可用，没有任何问题。|3016814|<?php
function+test()+{
++++echo+$_ENV["user"];
}|code-block|syntax|javascript|3016815|“全局变量不好”的一般规则在PHP中通常被修改为“全局变量不好，但超全局变量还可以”，只要没有滥用它们。(所有这些变量都是可写的，所以如果你真的很糟糕，可以用它们来避免依赖注入。)|3016816|不能保证这些变量一定存在；管理员可以使用php.ini中的variables_order+directive禁用部分或全部变量，但这并不常见。|3016817|3016818|一份当前的超全球化列表：|3016819|3016820|$GLOBALS+-当前script|unordered-list-item|3016821|$_SERVER中的所有全局变量-服务器上的信息和在environment|3016822|$_GET的查询字符串中传递的执行URL值。无论使用哪种HTTP方法作为HTTP+POST请求中传递的request|3016823|$_POST值，使用PHP|3016824|$_REQUEST内部存储的当前request|3016825|$_SESSION会话变量(通常是$_GET和$_POST的组合，但有时也是$_COOKIES+)传递HTTP+POST请求中传递的multipart/form-data+MIME+type|3016826|$_COOKIE文件。内容由php.ini.|3016827|$_ENV中的request_order+directive确定-即当前script|3016828|的环境变量|3016829|entityMap|0|LINK|mutability|MUTABLE|url|https://www.php.net/manual/en/language.variables.scope.php|1|https://php.net/manual/en/language.variables.superglobals.php|2|https://www.php.net/manual/en/ini.core.php#ini.variables-order|3|https://www.php.net/manual/en/ini.core.php#ini.request-order^0|L|A|0|0|S|6|Z|5|15|9|21|6|A|C|1|0|0|0|0|K|7|T|F|T|P|2|0|0|0|0|0|8|0|0|8|0|0|5|0|0|6|0|0|9|0|0|9|H|5|N|6|12|9|1U|J|0|0|8|E|7|0|0|5|7|D|7|N|3|0|0^^$0|@$1|2|3|4|5|6|7|1T|8|@]|9|@$A|1U|B|1V|1|1W]]|C|$]]|$1|D|3|E|5|6|7|1X|8|@$A|1Y|B|1Z|F|G]|$A|20|B|21|F|G]|$A|22|B|23|F|G]|$A|24|B|25|F|G]]|9|@$A|26|B|27|1|28]]|C|$]]|$1|H|3|I|5|6|7|29|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|2A|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|2B|8|@]|9|@]|C|$]]|$1|Q|3|R|5|6|7|2C|8|@$A|2D|B|2E|F|G]|$A|2F|B|2G|F|G]]|9|@$A|2H|B|2I|1|2J]]|C|$]]|$1|S|3|-4|5|6|7|2K|8|@]|9|@]|C|$]]|$1|T|3|U|5|6|7|2L|8|@]|9|@]|C|$]]|$1|V|3|-4|5|6|7|2M|8|@]|9|@]|C|$]]|$1|W|3|X|5|Y|7|2N|8|@$A|2O|B|2P|F|G]]|9|@]|C|$]]|$1|Z|3|10|5|Y|7|2Q|8|@$A|2R|B|2S|F|G]]|9|@]|C|$]]|$1|11|3|12|5|Y|7|2T|8|@$A|2U|B|2V|F|G]]|9|@]|C|$]]|$1|13|3|14|5|Y|7|2W|8|@$A|2X|B|2Y|F|G]]|9|@]|C|$]]|$1|15|3|16|5|Y|7|2Z|8|@$A|30|B|31|F|G]]|9|@]|C|$]]|$1|17|3|18|5|Y|7|32|8|@$A|33|B|34|F|G]|$A|35|B|36|F|G]|$A|37|B|38|F|G]|$A|39|B|3A|F|G]|$A|3B|B|3C|F|G]]|9|@]|C|$]]|$1|19|3|1A|5|Y|7|3D|8|@$A|3E|B|3F|F|G]|$A|3G|B|3H|F|G]]|9|@]|C|$]]|$1|1B|3|1C|5|Y|7|3I|8|@$A|3J|B|3K|F|G]|$A|3L|B|3M|F|G]]|9|@$A|3N|B|3O|1|3P]]|C|$]]|$1|1D|3|1E|5|6|7|3Q|8|@]|9|@]|C|$]]|$1|1F|3|-4|5|6|7|3R|8|@]|9|@]|C|$]]]|1G|$1H|$5|1I|1J|1K|C|$1L|1M]]|1N|$5|1I|1J|1K|C|$1L|1O]]|1P|$5|1I|1J|1K|C|$1L|1Q]]|1R|$5|1I|1J|1K|C|$1L|1S]]]]

I won't post a complete answer to the question, as the existing ones and the <a href="https://www.php.net/manual/en/language.variables.scope.php" rel="nofollow noreferrer">PHP manual</a> do a great job of explaining most of this. 

But one subject that was missed was that of <a href="https://php.net/manual/en/language.variables.superglobals.php" rel="nofollow noreferrer">superglobals</a>, including the commonly used <code>$_POST</code>, <code>$_GET</code>, <code>$_SESSION</code>, etc. These variables are arrays that are always available, in any scope, without a <code>global</code> declaration.

For example, this function will print out the name of the user running the PHP script. The variable is available to the function without any problem.

<pre><code>&lt;?php
function test() {
 echo $_ENV["user"];
}
</code></pre>

The general rule of "globals are bad" is typically amended in PHP to "globals are bad but superglobals are alright," as long as one is not misusing them. (All these variables are writable, so they could be used to avoid dependency injection if you were really terrible.)

These variables are not guaranteed to be present; an administrator can disable some or all of them using the <a href="https://www.php.net/manual/en/ini.core.php#ini.variables-order" rel="nofollow noreferrer"><code>variables_order</code> directive</a> in <code>php.ini</code>, but this is not common behaviour.

<hr>

A list of current superglobals:

<ul>
<li><code>$GLOBALS</code> - All the global variables in the current script</li>
<li><code>$_SERVER</code> - Information on the server and execution environment</li>
<li><code>$_GET</code> - Values passed in the query string of the URL, regardless of the HTTP method used for the request</li>
<li><code>$_POST</code> - Values passed in an HTTP POST request with <code>application/x-www-form-urlencoded</code> or <code>multipart/form-data</code> MIME types</li>
<li><code>$_FILES</code> - Files passed in an HTTP POST request with a <code>multipart/form-data</code> MIME type</li>
<li><code>$_COOKIE</code> - Cookies passed with the current request</li>
<li><code>$_SESSION</code> - Session variables stored internally by PHP</li>
<li><code>$_REQUEST</code> - Typically a combination of <code>$_GET</code> and <code>$_POST</code>, but sometimes <code>$_COOKIES</code>. The content is determined by the <a href="https://www.php.net/manual/en/ini.core.php#ini.request-order" rel="nofollow noreferrer"><code>request_order</code> directive</a> in <code>php.ini</code>.</li>
<li><code>$_ENV</code> - The environment variables of the current script</li>
</ul>

<blockquote>
 Note: This is a reference question for dealing with variable scope in PHP. Please close any of the many questions fitting this pattern as a duplicate of this one.
</blockquote>

What is "variable scope" in PHP? Are variables from one .php file accessible in another? Why do I sometimes get "undefined variable" errors?

Reference: What is variable scope, which variables are accessible from where and what are "undefined variable" errors?

服务器

这是一个在中处理变量作用域的参考问题。请将符合此模式的许多问题中的任何一个作为此模式的副本。PHP中的“变量作用域”是什么？一个.php文件中的变量可以在另一个文件中访问吗？为什么有时我会得到“未定义的变量”错误？

问参考:什么是变量作用域，哪些变量可以从哪里访问，什么是“未定义的变量”错误？
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