Importing PHP code in Joomla Component development

Can't figure out how to import php files into my joomla component- all of these fail:

• require_once('code.php');
• require_once(dirname(FILE).DS.'code.开发者_C百科php');
• require_once(JPATH_COMPONENT.DS.'code.php' );

Any ideas? thanks

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require_once(JPATH_COMPONENT_SITE.'/path/inside/your/component/folder.php');

Also - don't use DS - it is deprecated in Joomla 3.0

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Try jimport, see Joomla's docs on this: http://docs.joomla.org/Jimport

jimport('joomla.application.component.controller');

This will include the php file "/libraries/joomla/application/component/controller.php".

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Usually these are included in a helper.php file

require_once dirname(__FILE__).'/helper.php';