Detailed explanation of $$ in php

This article introduces to you the explanation of "$$" in the variable variable $$str in PHP. It is very simple and practical, and comes with simple examples. I hope to be helpful.

This way of writing is called a variable variable

Sometimes it is very convenient to use variable variable names. That is, the variable name of a variable can be set and used dynamically. An ordinary variable is set through declaration, for example:

<?php
$a = "hello";
?>

A variable variable obtains the value of an ordinary variable as the variable name of the variable variable. In the above example, hello can be used as a variable variable after using two dollar signs ($). For example:

<?php
$$a = "world";
?>

At this time, two variables are defined: the content of $a is "hello" and the content of $hello is "world". Therefore, it can be expressed as:

<?php
echo "$a ${$a}";
?>

The following writing is more accurate and will output the same result:

<?php
echo "$a $hello";
?>

They will both output: hello world.

To use mutable variables with arrays, an ambiguity must be resolved. This is when writing $$a[1], the parser needs to know whether it wants $a[1] as a variable, or whether it wants $$a as a variable and extracts the variable with index [1] value. The syntax to solve this problem is to use ${$a[1]} for the first case and ${$a}[1] for the second case.

Related recommendations:

Beginners to learn PHP variables, constants, arrays, functions

PHP variables

A brief discussion on the characters available for PHP variables_PHP tutorial

The above is the detailed content of Detailed explanation of $$ in php. For more information, please follow other related articles on the PHP Chinese website!