Common Functions

:param	string	$version: Version number
:returns:	TRUE if the running PHP version is at least the one specified or FALSE if not
:rtype:	bool

Determines if the PHP version being used is greater than the
supplied version number.

Example::

	if (is_php('5.5'))
	{
		echo json_last_error_msg();
	}

Returns boolean TRUE if the installed version of PHP is equal to or
greater than the supplied version number. Returns FALSE if the installed
version of PHP is lower than the supplied version number.

:param	string	$file: File path
:returns:	TRUE if the path is writable, FALSE if not
:rtype:	bool

``is_writable()`` returns TRUE on Windows servers when you really can't
write to the file as the OS reports to PHP as FALSE only if the
read-only attribute is marked.

This function determines if a file is actually writable by attempting
to write to it first. Generally only recommended on platforms where
this information may be unreliable.

Example::

	if (is_really_writable('file.txt'))
	{
		echo "I could write to this if I wanted to";
	}
	else
	{
		echo "File is not writable";
	}

.. note:: See also `PHP bug #54709 <https://bugs.php.net/bug.php?id=54709>`_ for more info.

:param	string	$key: Config item key
:returns:	Configuration key value or NULL if not found
:rtype:	mixed

The :doc:`Config Library <../libraries/config>` is the preferred way of
accessing configuration information, however ``config_item()`` can be used
to retrieve single keys. See :doc:`Config Library <../libraries/config>`
documentation for more information.

:param	mixed	$message: Error message
:param	int	$status_code: HTTP Response status code
:param	string	$heading: Error page heading
:rtype:	void

This function calls ``CI_Exception::show_error()``. For more info,
please see the :doc:`Error Handling <errors>` documentation.

:param	string	$page: URI string
:param	bool	$log_error: Whether to log the error
:rtype:	void

This function calls ``CI_Exception::show_404()``. For more info,
please see the :doc:`Error Handling <errors>` documentation.

:param	string	$level: Log level: 'error', 'debug' or 'info'
:param	string	$message: Message to log
:rtype:	void

This function is an alias for ``CI_Log::write_log()``. For more info,
please see the :doc:`Error Handling <errors>` documentation.

:param	int	$code: HTTP Response status code
:param	string	$text: A custom message to set with the status code
:rtype:	void

Permits you to manually set a server status header. Example::

	set_status_header(401);
	// Sets the header as:  Unauthorized

`See here <https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html>`_ for
a full list of headers.

:param	string	$str: Input string
:param	bool	$url_encoded: Whether to remove URL-encoded characters as well
:returns:	Sanitized string
:rtype:	string

This function prevents inserting NULL characters between ASCII
characters, like Java\\0script.

Example::

	remove_invisible_characters('Java\\0script');
	// Returns: 'Javascript'

:param	mixed	$var: Variable to escape (string or array)
:returns:	HTML escaped string(s)
:rtype:	mixed

This function acts as an alias for PHP's native ``htmlspecialchars()``
function, with the advantage of being able to accept an array of strings.

It is useful in preventing Cross Site Scripting (XSS).

:returns:	An associative array of file types
:rtype:	array

This function returns a *reference* to the MIMEs array from
*application/config/mimes.php*.

:returns:	TRUE if currently using HTTP-over-SSL, FALSE if not
:rtype:	bool

Returns TRUE if a secure (HTTPS) connection is used and FALSE
in any other case (including non-HTTP requests).

:returns:	TRUE if currently running under CLI, FALSE otherwise
:rtype:	bool

Returns TRUE if the application is run through the command line
and FALSE if not.

.. note:: This function checks both if the ``PHP_SAPI`` value is 'cli'
	or if the ``STDIN`` constant is defined.

:param	string	$function_name: Function name
:returns:	TRUE if the function can be used, FALSE if not
:rtype:	bool

Returns TRUE if a function exists and is usable, FALSE otherwise.

This function runs a ``function_exists()`` check and if the
`Suhosin extension <http://www.hardened-php.net/suhosin/>` is loaded,
checks if it doesn't disable the function being checked.

It is useful if you want to check for the availability of functions
such as ``eval()`` and ``exec()``, which are dangerous and might be
disabled on servers with highly restrictive security policies.

.. note:: This function was introduced because Suhosin terminated
	script execution, but this turned out to be a bug. A fix
	has been available for some time (version 0.9.34), but is
	unfortunately not released yet.