Is fullfile(0,0) undocumented behavior or bug?

What is the purpose, if any, of non-char inputs to fullfile?

 >> fullfile(0)
  > In fullfile>refinePath (line 93)
    In fullfile (line 38) 
    Warning: Inputs must be character arrays or cell arrays of strings. 
  ans =
   0
 >> fullfile(0,0)
 ans =
 \ 
 >> fullfile(0,0,0)
 ans =
 \ \ 
 >> fullfile(0,0,0,0)
 ans =
 \ \ \

etc. This is the behavior in R2014b and R2016b on Windows 7 (only versions I tested).

Answer 1

[Jan]

This is a bug. fullfile should contain a test, if all inputs are strings or character vectors. This happens for 1 input directly, but for multiple inputs, file sepearators are appended at first such that the elements are converted to character vectors implicitely.

I assume the warning is not correct also, but only a hard error is sufficient to stop the user driving fullfile beyond its purpose.

[Naor Movshovitz]

Agreed. I sent a bug report. FYI one way this is likely to occur is when a user cancels a file selection dialog, e.g.

[fname, pname] = uigetfile;
filename = fullfile(pname, fname);

uigetfile returns 0 when dialog closes with no file selected.

[Jan]

uigetfile should be accompanied by a check of a abortion under all circumstances:

[fname, pname] = uigetfile;
if isequal(fname,0) || isequal(pname,0)
  disp('User pressed cancel')
  ...

Omitting this test would be a crude programming style.

[Walter Roberson]

More generally, isnumeric(fname) instead of comparing to 0.