PHP session seems not to keep posted form values - php

Question

Ladies and gents,
I found a very strange behavior which I cannot explain:
Assume that you have
multiple form elements on your page, maybe rendered by php
each form has one input field with an unique name
on the beginning of that page a session will be started
you store every posted input value in the $_SESSION variable
like this:
<?php
session_start();
$_SESSION["Test"] = "Hello";
foreach ($_POST as $name => $value) {
//echo "_POST: " . $name . ":" . $value . "<br>";
$_SESSION[$name] = $value;
//session_commit();
}
for ($i = 0; $i < 10; $i++) {
echo "<form action=\"multiform.php\" method=\"post\">Value for input $i: <input type=\"text\" name=\"input".$i."\"></form>\n";
}
print_r($_SESSION);
?>
If you use the above code, only the "Test" = "Hallo" will persist after the refresh of the page. Regardless which input value has been posted and stored into the session by the foreach, it will be gone after refresh.
Now the interesting part:
If you add a name to the form like this...
echo "<form name=\"form$i\" action=\"multiform.php\" method=\"post\">Value for input $i: <input type=\"text\" name=\"input".$i."\"></form>\n";
...the posted values will be stored then.
But why?
What has the form name to do with the persistence of the $_SESSION?
EDIT: If the input name only contains numbers, the problem seems to arraise:
<input type=\"text\" name=\"$i\">
Thanks for clarifyng this.
Jan
EDIT2:
If the accessor key for the $_SESSION array only contains numbers, php obviously does not persist the values, so something like this, won't be stored:
<?php
session_start();
for ($i = 1; $i < 10; $i++)
{
$_SESSION[$i] = "Hello $i";
}
?>
The confusing part is, if you do a
print_r($_SESSION)
just after the for loop, it will show 1-10 with Hello 1..10...
Though, after refresh it's gone...

Answer 1

The keys in the $_SESSION associative array are subject to the same limitations as regular variable names in PHP, i.e. they cannot start with a number and must start with a letter or underscore.
Found at http://php.net/manual/en/session.examples.basic.php

Answer 2

Could the problem be the integer as a form name as your edit comment suggests? If you serialize a form using PHP you end up with a variable which name is an integer and PHP's variable name cannot be a plain number. If your problem doesn't persist with a naming convention such as <input type=\"text\" name=\"sometext_$i\">, you should stop using plain numbers as a form element name.
It's also a good idea to give the form fields descriptive names. Form field named "1" or "2" doesn't really tell you anything about the containing value.

Answer 3

This is correct; you can not use a numeric-only key in $_SESSION. Trying to do so with error_reporting on highest level and display_errors set to true will yield a notice:
PHP Notice: Unknown: Skipping numeric key 0 in Unknown on line 0
It does store it in the $_SESSION array, but not actually in the session. Although strange behaviour, the notice is descriptive enough. The fix is easy, by the way, just create an array in $_SESSION['numbers'], for example.
<?php
session_start();
for ($i = 1; $i < 10; $i++) {
$_SESSION['numbers'][$i] = "Hello $i";
}
var_dump( $_SESSION['numbers'] );