What does $$ (dollar dollar or double dollar) means in PHP ?
The $x (single dollar) is the normal variable with the name x that stores any value like string, integer, float, etc. The $$x (double dollar) is a reference variable that stores the value which can be accessed by using the $ symbol before the $x value. These are called variable variables in PHP.
Variable Variables:- Variable variables are simply variables whose names are dynamically created by another variable’s value.
From the given figure below, it can be easily understood that:
- $x stores the value “Geeks” of String type.
- Now reference variable $$x stores the value “for Geeks” in it of String type.
So, the value of “for zambiatek” can be accessed in two ways which are listed below:
- By using the Reference variable directly. Example: echo $$x;
- By using the value stored at variable $x as a variable name for accessing the “for Geeks” value. Example: echo $Geeks; which will give output as “for Geeks” (without quote marks).
Examples:
Input : $x = "Geeks";
$$x = for Geeks;
echo "$x ";
echo "$$x;";
echo $Geeks;
Output : Geeks
for Geeks
for Geeks
Input : $x = "Rajnish";
$$x = "Noida";
echo "$x lives in " . $Rajnish;
Output : Rajnish lives in Noida
Below are examples illustrating the use of $ and $$ in PHP:
Example-1:
php
<?php // Declare variable and initialize it$x = "Geeks"; // Reference variable$$x = "zambiatek";// Display value of xecho $x . "\n"; // Display value of $$x ($Geeks)echo $$x . "\n"; // Display value of $Geeksecho "$Geeks";?> |
Output:
Geeks zambiatek zambiatek
Example-2:
php
<?php // Declare variable and initialize it$var = "Geeks"; // Reference variable${$var}="zambiatek"; // Use double reference variable${${$var}}="computer science";// Display the value of variableecho $var . "\n"; echo $Geeks . "\n"; echo $zambiatek . "\n"; // Double referenceecho ${${$var}}. "\n"; ?> |
Output:
Geeks zambiatek computer science computer science
