PHP/CSS help

Hi,

I have a list item as a menu in my header.php file. I need a php function that allows me to set the class of the anchor tag to “active” based on which page/URL is currently loaded. I don’t mind if this is done by page ID, although would prefer to use URL so that I could have custom permalinks of domain/%postname%.

Any ideas welcome. So far I can get it to set all pages of a certain ID to active but that must mean I have got my statement being true no matter what page you are on.

Hope that makes sense?

Thanks in advance…