strval
unset
Variable handling Functions
PHP Manual

# unserialize

Creates a PHP value from a stored representation

### Description

mixed unserialize ( string `$str` )

unserialize takes a single serialized variable and converts it back into a PHP value.

### Parameters

`str`

  The serialized string.

  If the variable being unserialized is an object, after successfully reconstructing the object PHP will automatically attempt to call the __wakeup() member function (if it exists).

  > Note: unserialize_callback_func directive

  > It's possible to set a callback-function which will be called, if an undefined class should be instantiated during unserializing. (to prevent getting an incomplete object "__PHP_Incomplete_Class".) Use your php.ini, ini_set or .htaccess to define 'unserialize_callback_func'. Everytime an undefined class should be instantiated, it'll be called. To disable this feature just empty this setting.

### Return Values

The converted value is returned, and can be a boolean, integer, float, string, array or object.

In case the passed string is not unserializeable, `FALSE` is returned and `E_NOTICE` is issued.

### Changelog

Version | Description
--- | ---
4.2.0 | The directive unserialize_callback_func became available.

### Examples

Example #1 unserialize example

`<?php
// Here, we use unserialize() to load session data to the
// $session_data array from the string selected from a database.
// This example complements the one described with serialize().
$conn = odbc_connect("webdb", "php", "chicken");
$stmt = odbc_prepare($conn, "SELECT data FROM sessions WHERE id = ?");
$sqldata = array($_SERVER['PHP_AUTH_USER']);
if (!odbc_execute($stmt, $sqldata) || !odbc_fetch_into($stmt, $tmp)) {
// if the execute or fetch fails, initialize to empty array
$session_data = array();
} else {
// we should now have the serialized data in $tmp[0].
$session_data = unserialize($tmp[0]);
if (!is_array($session_data)) {
// something went wrong, initialize to empty array
$session_data = array();
}
}
?>`

Example #2 unserialize_callback_func example

`<?php
$serialized_object='O:1:"a":1:{s:5:"value";s:3:"100";}';
// unserialize_callback_func directive available as of PHP 4.2.0
ini_set('unserialize_callback_func', 'mycallback'); // set your callback_function
function mycallback($classname)
{
// just include a file containing your classdefinition
// you get $classname to figure out which classdefinition is required
}
?>`

### Notes

Warning

`FALSE` is returned both in the case of an error and if unserializing the serialized `FALSE` value. It is possible to catch this special case by comparing `str` with serialize(false) or by catching the issued `E_NOTICE`.

Warning

Do not pass untrusted user input to unserialize. Unserialization can result in code being loaded and executed due to object instantiation and autoloading, and a malicious user may be able to exploit this. Use a safe, standard data interchange format such as JSON (via json_decode and json_encode) if you need to pass serialized data to the user.

### See Also

- serialize
- Autoloading Objects
- unserialize_callback_func
- __wakeup()