Using variable to access multidimensional $_POST - php

Question

Consider this code:
$var = 'test';
$_POST[$test]; // equals $_POST['test']
How can I access with the same method this variable:
$_POST['test'][0];
$var = 'test[0]'; clearly doesn't work.
EDIT
Let me give a bit more information. I've got a class that builds a form.
An element is added like this:
//$form->set_element(type, name, defaultValue);
$form->set_element('text', 'tools', 'defaultValue');
This results into :
<input type="text" name="tools" value="defaultValue" />
In my class I set the value: if the form is posted, use that value, if not, use the default:
private function set_value( $name, $value='' ) {
if( $_SERVER['REQUEST_METHOD'] == 'POST' )
return $_POST[$name];
else
return $value;
}
When I want to add multiple "tools", I would like to use:
$form->set_element('text', 'tools[0]', 'defaultValue');
$form->set_element('text', 'tools[1]', 'defaultValue');
$form->set_element('text', 'tools[2]', 'defaultValue');
But in the set_value function
that gives $_POST['tools[0]'] instead of $_POST['tools'][0]

Answer 1

Use any number of variables in [] to access what you need:
$test = 'test';
$index = 0;
var_dump($_POST[$test][$index]);
$test = 'test';
$index = 0;
$subkey = 'key'
var_dump($_POST[$test][$index][$subkey]);
And so on.
There's no special function to achieve what you want, so you should write something, for example:
$key = 'test[0]';
$base = strstr($key, '[', true); // returns `test`
$ob_pos = strpos($key, '[');
$cb_pos = strpos($key, ']');
$index = substr($key, $ob_pos + 1, $cb_pos - $ob_pos - 1);
var_dump($arr[$base][$index]);
Edit by LinkinTED
$key = 'test[0]';
$base = $n = substr($name, 0, strpos($key, '[') );
preg_match_all('/\[([^\]]*)\]/', $key, $parts);
var_dump($arr[$base][$parts[1][0]]);

Answer 2

See how when you did $_POST['test'][0]; you just added [0] to the end? As a separate reference.
You have to do that.
$_POST[$test][0];
If you need both parts in variables then you need to use multiple variables, or an array.
$var = Array( "test", "0" );
$_POST[$test[0]][$test[1]];

Answer 3

Each dimension of an array is called by specifying the key or index together with the array variable.
You can reference a 3 dimensional array's element by mentioning the 3 indexes of the array.
$value = $array['index']['index']['index'];
Like,
$billno = $array['customers']['history']['billno'];
You can also use variables which has the index values that can be used while specifying the array index.
$var1 = 'customers';
$var2 = 'history';
$var3 = 'billno';
$billno = $array[$var1][$var2][$var3];