How to distinguish between binary and ASCII file on file opening?

From: CFF (cffung_at_myrealbox.com)
Date: 08/10/04 

Date: 9 Aug 2004 20:26:14 -0700

I am writing an applicatioin that will need to distinguish between
binary and ASCII file to be loaded from hard disk so that different
processing is applied to different type of file.

Is there any simple way to identify the type of file during the file
opening process? Thank you.

CFF