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# CLXII. Variable Handling Functions

# Introduction

For information on how variables behave, see the Variables entry in the Language Reference section of the manual.

# Requirements

No external libraries are needed to build this extension.

# Installation

There is no installation needed to use these functions; they are part of the PHP core.

# Runtime Configuration

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

Table 1. 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_* constants, see the Appendix G.

Here's a short explanation of the configuration directives.

unserialize_callback_func string

  The unserialize() callback function will called (with the undefined class' name as parameter), if the unserializer finds an undefined class which should be instanciated. A warning appears if the specified function is not defined, or if the function doesn't include/implement the missing class. So only set this entry, if you really want to implement such a callback-function.

  See also unserialize().

# Resource Types

This extension has no resource types defined.

# Predefined Constants

This extension has no constants defined.

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