Save function should check output file

[Marco Mattiolo]

Hi, and thank you all for writing/maintaining/supporting Octave!

I've had a problem with the "save" function: after extracting results 
from a FEMM
simulation (using OctaveFemm commands inside a script), variables were:
Variables in the current scope:

   Attr Name         Size                     Bytes  Class
   ==== ====         ====                     =====  =====
        out    3732445x14                 418033840  double
        x            1x3732445             29859560  double
        y            1x3732445             29859560  double

Total is 59719120 elements using 477752960 bytes

which were saved (at the end of the script) with "save dati.mat x y out" to
-rwxr-xr-x 1 marcus89 root 502M ago 29 04:05 dati.mat

I copied dati.mat to my home and tried loading it inside another Octave 
session:

octave:3> load dati.mat
error: load: failed to load matrix constant
error: load: trouble reading ascii file 'dati.mat'
error: load: reading file dati.mat
octave:3> whos
Variables in the current scope:

   Attr Name        Size                     Bytes  Class
   ==== ====        ====                     =====  =====
        x           1x3732445             29859560  double
        y           1x3732445             29859560  double

Total is 7464890 elements using 59719120 bytes

Got back to first Octave session and tried saving again (all variables 
in a file or one variable per file),
but getting empty files.

octave:2> save x.mat x
octave:3> exit
$ ls -lh
-rwxr-xr-x 1 marcus89 root    0 ago 29 14:19 x.mat


After a search in this list's archives, tried "cd" to my home directory 
and then saving again ("save data"):

-rw-r--r-- 1 marcus89 marcus89 682M ago 29 13:02 data
-rwxr-xr-x 1 marcus89 marcus89 502M ago 29 04:05 dati.mat

This time variables were saved right:

octave:3> clear all
octave:4> load data
octave:5> whos
Variables in the current scope:

   Attr Name         Size                     Bytes  Class
   ==== ====         ====                     =====  =====
        out    3732445x14                 418033840  double
        x            1x3732445             29859560  double
        y            1x3732445             29859560  double

Total is 59719120 elements using 477752960 bytes

So, probably during script's runtime (~10-12h) something,
related to usb-key's partition on which Octave script and input files 
were, has changed,
bringing to a wrong (unusable) output file and to the inability to save 
variables (getting empty files).
These problems got solved moving to another directory (probably because 
of the full write access?).

My question is: why doesn't Octave's save function complain, if it 
doesn't have full writing access to the actual directory?
Or check validity of the output file?
Wouldn't it be better, more reliable?

Thank you
Marco Mattiolo