用strrchr /substr+strrpos /array_pop+explode /pathinfo+extension / substr+strrev+strpos解决取出扩展名的问题

get_ext1($file_name){  return strrchr($file_name,'.');}get_ext2($file_name) {return substr($file_name,strrpos($file_name,'.'))}get_ext3($file_name) {return array_pop(explode('.',$file_name));}get_ext4($file_name){//return pathinfo($file_name,PATHINFO_EXTENSION);$p = pathinfo($file_name);return $p['extension'];}get_ext5($file_name) {return strrev(substr(strrev($file_name),0,strpos(strrev($file_name),'.')));}