Difference between $name and $$name?

Tomos Wyn

13 years ago

PHP: Variable variables - Manual

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Workman

13 years ago

Tomos is right, the $$ represents a variable variable. Here's how they work

$foo = 'bar';
$name = 'foo';

echo $name; // foo
echo $$name; //bar
echo $foo; //bar

You first assign the value of a variable, $name, to the name of another variable. When you set $name to a value, it will replace that variablename with the value of the variable you provide it.

$test = 'asdf';
$$test = 'I am changing asdf\'s value!';
echo $$test; // I am changing asdf's value!
echo $test; // asdf
echo $asdf; // I am changing asdf's value!

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1 reply

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manimoor 13 years ago

Hi..Thanks for your help...

The above coding is easily understandable..

It nice explanations...Thanks a lot.....
- Thanks
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ussher

13 years ago

I'd add the suggestion to not use this style if you can avoid it, it makes the code hard to read without a step through debugger.

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1 reply

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Defrag

13 years ago

Originally Posted by ussher

I'd add the suggestion to not use this style if you can avoid it, it makes the code hard to read without a step through debugger.

This. Seriously, don't be that guy. PHP is supposedly designed with the "KISS Principle" (Keep It Simple Stupid), but they allow some utterly attrocious things. I truly can't think of a reason you'd ever want to do this that can't be done cleaner and/or simpler in another way.

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2 replies

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powerspike

13 years ago

Originally Posted by Defrag

This. Seriously, don't be that guy. PHP is supposedly designed with the "KISS Principle" (Keep It Simple Stupid), but they allow some utterly attrocious things. I truly can't think of a reason you'd ever want to do this that can't be done cleaner and/or simpler in another way.

I have to completely agree with this! The absolute worse thing you can do is use it with user input (ie form submit) and you have a complete disaster on your hands.

Never trust user data, and using $$ under $ is one way to ensure you lose your hair over night.

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Workman

13 years ago

Originally Posted by Defrag

This. Seriously, don't be that guy. PHP is supposedly designed with the "KISS Principle" (Keep It Simple Stupid), but they allow some utterly attrocious things. I truly can't think of a reason you'd ever want to do this that can't be done cleaner and/or simpler in another way.

I can think of a couple of places you could use it, but the only one I feel innocent in getting away with would be in a debugging tool of some sort.

Originally Posted by Sarten

$ name is variable where as $$ name is reference variable

Nope. &$name is a variable passed (or accepted in a function call) as a reference.
[ PHP: References Explained ]