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## Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

Variables Configuration Options
Name | Default | Changeable | Changelog
--- | --- | --- | ---
unserialize_callback_func | NULL | PHP_INI_ALL | Available since PHP 4.2.0.

For further details and definitions of the PHP_INI_* modes, see the Where a configuration setting may be set.

Here's a short explanation of the configuration directives.

`unserialize_callback_func` string

  The callback specified is called when unserialize() attempts to use an undefined class. A warning appears if the specified callback function is not defined, or if the callback function fails to define the missing class.

  See also unserialize() and Autoloading Objects.

Installation
Resource Types
Installing/Configuring
PHP Manual