# CodeIgniter User Guide Version 2.1.0

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# Common Functions

CodeIgniter uses a few functions for its operation that are globally defined, and are available to you at any point. These do not require loading any libraries or helpers.

## is_php('version_number')

is_php() determines of the PHP version being used is greater than the supplied version_number.

`if (is_php('5.3.0'))
{
$str = quoted_printable_encode($str);
}`

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.

## is_really_writable('path/to/file')

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.

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

## config_item('item_key')

The Config library is the preferred way of accessing configuration information, however config_item() can be used to retrieve single keys. See Config library documentation for more information.

## show_error('message'), show_404('page'), log_message('level', '`message`')

These are each outlined on the Error Handling page.

## set_status_header(code, 'text');

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

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

See here for a full list of headers.

## remove_invisible_characters($str)

This function prevents inserting null characters between ascii characters, like Java\0script.

## html_escape($mixed)

This function provides short cut for htmlspecialchars() function. It accepts string and array. To prevent Cross Site Scripting (XSS), it is very useful.