What is the use of $$ symbol in PHP? how to use? (code example)

We often use the $ symbol in PHP, so do you know the $$ symbol? The following article will take you to understand the $$ symbol, introduce what the $$ symbol is used in PHP, and how to use it. I hope it will be helpful to everyone.

The $$ symbol in PHP

In PHP, $var (single dollar) represents An ordinary variable named var, which stores any value such as string, integer, floating point, etc. And $$var (double dollar) is a reference variable used to store the value of $var. [Video tutorial recommendation: PHP tutorial]

Take an example to understand:

Use $var to store a String type value" PHP", and then use the reference variable $$var to store a String type value "PHP Chinese Network".

At this time, the value "Chinese Network" can be accessed in two ways:

1. Directly use reference variables. Example: echo $$var;

2. Access the value "PHP Chinese Network" by using the value "PHP" stored in the variable $var as the variable name. For example: echo $PHP; it will be output as "PHP Chinese Network" (without quotation marks).

Code example:

The following is an example of how to use $ and $ in PHP $:

Example 1:

<?php 
header("content-type:text/html;charset=utf-8");   
// 声明变量并初始化它
$var = "PHP";      
  
// 引用变量
$$var = "PHP中文网"; 
  
// 输出$var的值
echo $var . "<br>";  
  
// 输出$$var的值
echo $$var . "<br>";  
  
// 输出$PHP的值
echo "$PHP"; 
?>

Output:

Example 2:

<?php 
header("content-type:text/html;charset=utf-8");   
$name="Cat";  
${$name}="Dog";  
${${$name}}="Monkey";  
echo $name. "<br>";  
echo ${$name}. "<br>";  
echo $Cat. "<br>";  
echo ${${$name}}. "<br>";  
echo $Dog. "<br>";  
?>

Output:

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