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Variable Variables

by: Robert Berkowitz
|
September 28, 2000

During a recent project I discovered a totally new concept in programming for myself, variable variables. I needed to update multiple records from one page. After banging my head on the wall for quite some time, I stumbled across the variable variable and all my troubles went away!

Introduction

So, just what the heck is a variable variable anyway? According to the PHP manual, a variable variable takes the value of a variable and treats that as the name of a variable. While this may seem pretty straightforward, it can be a little confusing with so many uses of the word "variable" in one sentence. What the definition simply states is that you can set a variable -- x equals this -- and then set the variable variable, meaning you set the value of x as a new variable of x. In this example, the variable this would equal is cake. In PHP, this would be denoted as follows:

<?php

$x 
"this";
$
$x "is cake";

?>
The $$ is the syntax used in PHP for a variable variable. I can now call the two variables $x and $$x two ways.

<?php

echo "$x ${$x}";

?>

 

<?php

echo "$x $this";
    
?>
Both of these will return the string "this is cake". Notice that $$x is written as ${$x} in echo. This lets PHP know that you are using the variable $$x and not $ and $x.
Still scratching your head? Or maybe you get it, but want a more in depth and actually useful example? In the next section I will show you how variable variables may be used to edit multiple records on one page.

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