[RESOLVED] What does $$ do???

[ClarkF1]

I came across a script on the web for sorting arrays that has variable assignments using $$

I couldn't understand what it did????

Just curious whether anyone out there knows........it could be useful.

The script is one of the user comments on the array_multisort page.

It sorts multi-dimensional arrays really easily but I was wondering how it worked.

[bradgrafelman]

It references the name of a variable using another variable. For example:

$foo = 'bar';
$$foo = 'hi';
echo $bar; // outputs: hi

It's equivalent to using braces like so:

$foo = 'bar';
${$foo} = 'hi';
echo $bar; // again, outputs: hi

You can combine normal text with the value of a variable to set another variable, like so:

$foo = 'bar';
${'foo_' . $foo} = 'hello!';
echo $foo_bar; // outputs: hello!

[ClarkF1]

So using this:

foreach ($vals as $init)
  {
    $keyname = "sort$init";
    $$keyname = array();
  }

if $vals is an array containing (a,b,c,d,e) we would get

$sorta, $sortb, $sortc, $sortd and $sorte set as arrays would we???

[bradgrafelman]

Yes. You could condense those two lines inside your foreach() even further using the braces as I mentioned:

foreach ($vals as $init) 
  {
    ${'sort' . $init} = array();
  }