how wordpress generates permalinks as /%category%/%post%/

Question

I am not here to discuss the efficiency of using categories as the base for permalinks.

I would like to know in what file and what line is the code to how Wordpress picks out a category for the permalink if the post is in multiple categories. I asked this on IRC a while ago and I can't find the code anymore.

Thanks.

Answer 1

get_permalink in /wp-includes/link-template.php, line 80