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The unserialize of Variable Handling for PHP creates a PHP value from a stored representation.


unserialize ( string $str [, array $options ] ) : mixed



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.


Any options to be provided to unserialize(), as an associative array.

allowed_classesmixedEither 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.


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.




// 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();





ini_set('unserialize_callback_func', 'mycallback'); // set your callback_function

function mycallback($classname) {
    // just include a file containing your class definition
    // you get $classname to figure out which class definition is required