PHP preg replace only allow numbers

Question

How can I modify this existing preg_replace to only allow numbers?

function __cleanData($c)  {     return preg_replace("/[^A-Za-z0-9]/", "",$c); } 

Answer 1

I think you're saying you want to remove all non-numeric characters. If so, \D means "anything that isn't a digit":

preg_replace('/\D/', '', $c)