$$（美元或双美元）在 PHP 中是什么意思？
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What does $$ (dollar dollar or double dollar) mean in PHP?
提问by chicane
Example is a variable declaration within a function:
示例是函数内的变量声明：
global $$link;
What does $$mean?
什么$$意思？
回答by Pascal MARTIN
A syntax such as $$variableis called Variable Variable.
一种$$variable称为Variable Variable 的语法。
For example, if you consider this portion of code :
例如，如果您考虑这部分代码：
$real_variable = 'test';
$name = 'real_variable';
echo $$name;
You will get the following output :
您将获得以下输出：
test
Here :
这里 ：
$real_variablecontains test$namecontains the name of your variable :'real_variable'$$namemean "the variable thas has its name contained in$name"- Which is
$real_variable - And has the value
'test'
- Which is
$real_variable包含测试$name包含变量的名称：'real_variable'$$name意思是“变量名包含在$name”中- 这是
$real_variable - 并且具有价值
'test'
- 这是
EDIT after @Jhonny's comment :
在@Jhonny 的评论后编辑：
Doing a $$$?
Well, the best way to know is to try ;-)
做一个$$$？
好吧，最好的了解方法是尝试;-)
So, let's try this portion of code :
所以，让我们试试这部分代码：
$real_variable = 'test';
$name = 'real_variable';
$name_of_name = 'name';
echo $name_of_name . '<br />';
echo $$name_of_name . '<br />';
echo $$$name_of_name . '<br />';
And here's the output I get :
这是我得到的输出：
name
real_variable
test
So, I would say that, yes, you can do $$$;-)
所以，我会说，是的，你可以做到$$$;-)
回答by Rich
The inner $ resolves the a variable to a string, and the outer one resolves a variable by that string.
内部 $ 将 a 变量解析为字符串，外部 $ 将变量解析为该字符串。
So, consider this example
所以，考虑这个例子
$inner = "foo";
$outer = "inner";
The variable:
变量：
$$outer
would equal the string "foo"
将等于字符串“foo”
回答by Anthony Forloney
It's a variable's variable.
这是一个变量的变量。
<?php
$a = 'hello';
$$a = 'world'; // now makes $hello a variable that holds 'world'
echo "$a ${$a}"; // "hello world"
echo "$a $hello"; // "hello world"
?>
回答by Felix Kling
It creates a dynamic variable name. E.g.
它创建一个动态变量名。例如
$link = 'foo';
$$link = 'bar'; // -> $foo = 'bar'
echo $foo;
// prints 'bar'
(also known as variable variable)
（也称为可变变量）
回答by hsz
I do not want to repeat after others but there is a risk using $$:)
我不想在其他人之后重复，但使用有风险$$:)
$a = '1';
$$a = 2; // = 2 :)
So use it with head. :)
所以用头。:)
回答by Diego Santa Cruz Mendezú
this worked for me (enclose in square brackets):
这对我有用（用方括号括起来）：
$aInputsAlias = [
'convocatoria' => 'even_id',
'plan' => 'acev_id',
'gasto_elegible' => 'nivel1',
'rubro' => 'nivel2',
'grupo' => 'nivel3',
];
/* Manejo de los filtros */
foreach(array_keys($aInputsAlias) as $field)
{
$key = $aInputsAlias[$field];
${$aInputsAlias[$field]} = $this->request->query($field) ? $this->request->query($field) : NULL;
}
回答by Zach
It evaluates the contents of one variable as the name of another. Basically it gives you the variable whose name is stored in $link.
它将一个变量的内容评估为另一个变量的名称。基本上它为您提供名称存储在$link.
