I've built my XLL add-ins using the Excel C API for ages but not lately, and I've forgotten a detail.
The code line below assigns an error message string that will be returned by a function if a certain argument fails a certain error check:
result.val.str = "\043Time_in_years must be non-negative!"
The 043 in the code fragment is the length of the string "Time_in_years must be non-negative!" in some measure like degrees or radians or something like that. Maybe octal?
What I remember is that it is some kind of mathematical transform of the number of characters (including blank spaces) in the string message, 35 in the code fragment.
Any Excel C API power programmers out there?