(PHP 4, PHP 5, PHP 7, PHP 8)
unserialize — Creates a PHP value from a stored representation
unserialize() takes a single serialized variable and converts it back into a PHP value.
Do not pass untrusted user input to unserialize() regardless of the options
value of allowed_classes
. 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.
If you need to unserialize externally-stored serialized data, consider using hash_hmac() for data validation. Make sure data is not modified by anyone but you.
data
The serialized string.
If the variable being unserialized is an object, after successfully reconstructing the object PHP will automatically attempt to call the __unserialize() or __wakeup() methods (if one 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.
options
Any options to be provided to unserialize(), as an associative array.
Name | Type | Description |
---|---|---|
allowed_classes | mixed | Either an array of class names which should be accepted, false to accept no classes, or true to accept all classes. If this option is defined and unserialize() encounters an object of a class that isn't to be accepted, then the object will be instantiated as __PHP_Incomplete_Class instead. Omitting this option is the same as defining it as true : PHP will attempt to instantiate objects of any class. |
max_depth | int | The maximum depth of structures permitted during unserialization, and is intended to prevent stack overflows. The default depth limit is 4096 and can be disabled by setting max_depth to 0 . |
The converted value is returned, and can be a bool, int, float, string, array or object.
In case the passed string is not unserializeable, false
is returned and E_WARNING
is issued.
Objects may throw Throwables in their unserialization handlers.
Version | Description |
---|---|
8.3.0 | Now emits E_WARNING when the passed string is not unserializeable; previously E_NOTICE was emitted. |
7.4.0 | Added the max_depth element of options to set the maximum depth of structures permitted during unserialization. |
7.1.0 | The allowed_classes element of options ) is now strictly typed, i.e. if anything other than an array or a bool is given, unserialize() returns false and issues an E_WARNING . |
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
$serialized_object='O:1:"a":1:{s:5:"value";s:3:"100";}';
ini_set('unserialize_callback_func', 'mycallback'); // set your callback_function
function mycallback($classname)
{
// just include a file containing your class definition