textscan error only in loop: "Invalid file identifier. Use fopen to generate a valid file identifier"

Hi,

I am receiving textscan error when I create a loop to process and write my files. If I run each file individually without a loop, it works without any problem. If anyone knows what will be the reason of it?

"Error using textscan.Invalid file identifier. Use fopen to generate a valid file identifier."

[fname,pname] = uigetfile("MultiSelect","on",'*.dat')
fname=[pname, fname];
if isequal(fname,0)
   disp('User selected Cancel');
else
   disp(['User selected ', fullfile(pname, fname)]);
end
    
for k = 1 : length(fname)
fprintf('Now reading file %s\n', fname{k});
fid=fopen(fname{k},'r');
F=textscan(fid,'%f','HeaderLines',17);
Temp=F{1,1}
T_out = timetable(datetime(2018,1,17,0,0,10*(0:size(Temp,1)-1)'),Temp);
time_array=datetime("29-May-2018 00:00:00", "InputFormat","dd-MMM-uuuu HH:mm:ss")
summerstart=find(T_out.Time=="29-May-2018 00:00:00")
Tsummer=T_out([summerstart]:end,:)
[filepath,name,ext] = fileparts(fname)
writetimetable(Tsummer,[name 'r.csv'])  
end

Thanks a lot!

Answer 1

[Stephen23]

This will not work as you require:

fname=[pname, fname];

Instead you should use FULLFILE, to correctly handle the file separator character, for example:

[fnc,fpt] = uigetfile("MultiSelect","on",'*.dat');

if isequal(fnc,0)
   return
end

for k = 1:numel(fnc)
    fprintf('Now reading file %s\n', fnc{k});
    fnm = fullfile(fpt,fnc{k}); % better to use FULLFILE
    fid = fopen(fnm,'r');
    tmp = textscan(fid,'%f','HeaderLines',17);
    fclose(fid); % you need to FCLOSE every file
    .. etc 
end

[Cakil]

Thank you very much, I could not make a connection with fname=[pname, fname] and the textscan error but it works perfectly now :)

Answer 2

[Jonas]

use fclose(fid) at the end of the for loop

sometimes, if using a script a file remains open and you may not have the identifier anymore. in this case use fclose('all')

[Cakil]

Thank you, I tried both fclose(fid) and fclose('all') but still receiving the same error.