bcit-ci/CodeIgniter

################
Helper Functions
################

Helpers, as the name suggests, help you with tasks. Each helper file is
simply a collection of functions in a particular category. There are **URL
Helpers**, that assist in creating links, there are Form Helpers that help
you create form elements, **Text Helpers** perform various text formatting
routines, **Cookie Helpers** set and read cookies, File Helpers help you
deal with files, etc.

Unlike most other systems in CodeIgniter, Helpers are not written in an
Object Oriented format. They are simple, procedural functions. Each
helper function performs one specific task, with no dependence on other
functions.

CodeIgniter does not load Helper Files by default, so the first step in
using a Helper is to load it. Once loaded, it becomes globally available
in your :doc:`controller <../general/controllers>` and
:doc:`views <../general/views>`.

Helpers are typically stored in your **system/helpers**, or
**application/helpers directory**. CodeIgniter will look first in your
**application/helpers directory**. If the directory does not exist or the
specified helper is not located there CI will instead look in your
global *system/helpers/* directory.

Loading a Helper
================

Loading a helper file is quite simple using the following method::

    $this->load->helper('name');

Where **name** is the file name of the helper, without the .php file
extension or the "helper" part.

For example, to load the **URL Helper** file, which is named
**url_helper.php**, you would do this::

    $this->load->helper('url');

A helper can be loaded anywhere within your controller methods (or
even within your View files, although that's not a good practice), as
long as you load it before you use it. You can load your helpers in your
controller constructor so that they become available automatically in
any function, or you can load a helper in a specific function that needs
it.

.. note:: The Helper loading method above does not return a value, so
    don't try to assign it to a variable. Just use it as shown.

Loading Multiple Helpers
========================

If you need to load more than one helper you can specify them in an
array, like this::

    $this->load->helper(
        array('helper1', 'helper2', 'helper3')
    );

Auto-loading Helpers
====================

If you find that you need a particular helper globally throughout your
application, you can tell CodeIgniter to auto-load it during system
initialization. This is done by opening the **application/config/autoload.php**
file and adding the helper to the autoload array.

Using a Helper
==============

Once you've loaded the Helper File containing the function you intend to
use, you'll call it the way you would a standard PHP function.

For example, to create a link using the ``anchor()`` function in one of
your view files you would do this::

    <?php echo anchor('blog/comments', 'Click Here');?>

Where "Click Here" is the name of the link, and "blog/comments" is the
URI to the controller/method you wish to link to.

"Extending" Helpers
===================

To "extend" Helpers, create a file in your **application/helpers/** folder
with an identical name to the existing Helper, but prefixed with **MY\_**
(this item is configurable. See below.).

If all you need to do is add some functionality to an existing helper -
perhaps add a function or two, or change how a particular helper
function operates - then it's overkill to replace the entire helper with
your version. In this case it's better to simply "extend" the Helper.

.. note:: The term "extend" is used loosely since Helper functions are
    procedural and discrete and cannot be extended in the traditional
    programmatic sense. Under the hood, this gives you the ability to
    add to or or to replace the functions a Helper provides.

For example, to extend the native **Array Helper** you'll create a file
named **application/helpers/MY_array_helper.php**, and add or override
functions::

    // any_in_array() is not in the Array Helper, so it defines a new function
    function any_in_array($needle, $haystack)
    {
        $needle = is_array($needle) ? $needle : array($needle);

        foreach ($needle as $item)
        {
            if (in_array($item, $haystack))
            {
                return TRUE;
            }
            }

        return FALSE;
    }

    // random_element() is included in Array Helper, so it overrides the native function
    function random_element($array)
    {
        shuffle($array);
        return array_pop($array);
    }

Setting Your Own Prefix
-----------------------

The filename prefix for "extending" Helpers is the same used to extend
libraries and core classes. To set your own prefix, open your
**application/config/config.php** file and look for this item::

    $config['subclass_prefix'] = 'MY_';

Please note that all native CodeIgniter libraries are prefixed with **CI\_**
so DO NOT use that as your prefix.

Now What?
=========

In the Table of Contents you'll find a list of all the available Helper
Files. Browse each one to see what they do.