Thanks guys for your advice.

I am associating the names with C++ objects in memory and then returning the
name to the calling cell so that other functions can find the object in
memory, too. The idea was to change the name every time the C++ object
changes, that is, whenever the cell is recalculated. This way it is easy to
follow what's happening in the spreadsheet. This works quite neatly until
there are so many names that excel gets bloated.

Well, I can always recycle the names and thereby avoid performance problems.