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() determines of the PHP version being used is greater than the supplied version_number.
$str = quoted_printable_encode($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_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.
echo "I could write to this if I wanted to";
echo "File is not writable";
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.
Permits you to manually set a server status header. Example:
// Sets the header as: Unauthorized
See here for a full list of headers.
This function prevents inserting null characters between ascii characters, like Java\0script.
This function provides short cut for htmlspecialchars() function. It accepts string and array. To prevent Cross Site Scripting (XSS), it is very useful.