What are the various functions used in Codeigniter?

CodeIgniter - Interview Questions

The functions in Codeigniter are globally defined and freely available. Loading of libraries or helpers is not required when using these functions.

is_really_writable($file)
is_php($version)
html_escape($var)
config_item($key)
set_status_header($code[, $text = ”])
is_https()
remove_invisible_characters($str[, $url_encoded = TRUE])
is_cli()
get_mimes()