Re: Error while opening a .txt file

[N]

On Sun, 7 Jun 2020 14:46:58 +0200
Markus Mützel <markus.muetzel@gmx.de> wrote:

> Am 07. Juni 2020 um 14:37 Uhr schrieb "Andrew Janke":
> > On 6/7/20 8:19 AM, Markus Mützel wrote:
> > > Am 07. Juni 2020 um 14:13 Uhr schrieb "N":
> > >> Would suggest the following so that file is closed before exit in case 
> > >> of an error, as I remember there might be problems otherwise.
> > >>
> > >>
> > >> [fid msg] = fopen('data.txt', 'r');                % Open file
> > >> if(fid == -1)                                      % Error occured?
> > >>   error(msg)                                         % Throw error and 
> > >> show error messsage what went wrong
> > >> end
> > >>
> > >> try                                                % Start try block so 
> > >> that error could be catched and file closed
> > >>   data = textscan (fid, '% f', 'HeaderLines', 5);
> > >>   period_arr = data {1};
> > >> catch err                                          % Catch error in case 
> > >> it happen, rows below are not run then everything is OK
> > >>   fclose(fid);                                       % This is needed 
> > >> otherwise file is not closed then you make error in code and it is a 
> > >> problem
> > >>   rethrow(err)                                       % Rethrow the same 
> > >> error but here file have been closed before error
> > >> end
> > >>
> > >>
> > >> Nicklas SB Karlsson
> > >>
> > > Consider using "unwind_protect" instead of "try", or the fid will only be 
> > > closed if an error occurs.
> > > Or remember to fclose(fid) after the catch-block.
> > >
> > > Markus
> > >
> > >
> > >
> > Or onCleanup! It can make your code really concise.
> > 
> > file = 'data.txt';
> > [fid, msg] = fopen(file, 'r');
> > if fid == -1
> >   error('Failed opening file ''%s'': %s', file, msg);
> > end
> > RAII.fid = onCleanup(@() fclose(fid));  % automatically gets called when
> > RAII is cleared
> > data = textscan (fid, '% f', 'HeaderLines', 5);
> > period_arr = data {1};
> > % and that's it! no try/catch needed
> > 
> > Cheers,
> > Andrew
> > 
> 
> Or that.
> But keep in mind that this might not work in scripts unless you explicitly 
> clear the object returned by onCleanup when you are done.
> 
> Markus

If it does not get automatically cleared then function exit this must be a 
problem. Or?

Think files are closed automatically in C but not in Octave if I got it right.