Detecting type of SDTS file?

[Ben Discoe]

When somebody does a drag-and-drop of an SDTS file (*catd.ddf) into my
application, i need to quickly find out if it is a SDTS-DEM (in which case i
will load it with GDAL) or an SDTS-DLG (in which case i will load it with
OGR).

Is there any way to do this simply, short of the full process of attempting
to load the file with both GDAL and OGR and testing which operation fails?

-Ben