Open multiple files with fopen

I have written two codes in matlab:

The first one is:

files=dir('*.csv');

for i=1:length(files)
    fid(i)=fopen(files(i).name);
    files(i).values=textscan(fid(i), '%f %f','delimiter',',','HeaderLines',20,'MultipleDelimsAsOne',1);
end

and the second one is:

str='C:\Users\user\Measurements\Test';
folder_name=uigetdir(str);
files=dir(fullfile(folder_name,'*.csv'));

for i=1:length(files)
    fid(i)=fopen(files(i).name);
    files(i).values=textscan(fid(i), '%f %f','delimiter',',','HeaderLines',20,'MultipleDelimsAsOne',1);

end

The first code is saved in the same folder as the files that I want to open. The second code is saved outside the folder where the files are stored. But both should read the same files. In the first code the structure files.values is composed by a 1x2 cell. Both cells contain a column vector with numerical values The problem arises in the second code which sometimes gives me an error because fid=-1 or the column vectors in the structure files.values are empty.

How can I overcome this problem?

Answer 1

[Walter Roberson]

Is there a reason to keep the fid's around? Often you would fclose() right after the textscan. This can be important in preventing you from running out of files.

When you do the fopen() ask for the message output. Then test the fid and if it is -1, display the message (and the file name.)

Answer 2

[Giorgos Papakonstantinou]

Ok I corrected and I included the fclose() but I still get empty cells in the structure files.values. Why is that?

And also when I requested for a message I got this:

No such file or directory

which I can not explain it since the folder contains *.csv files and the folder exists since I use the uigetdir and I select the folder from the browser myself.

[Giorgos Papakonstantinou]

When I try to debug it. The command:

files=dir(fullfile(folder_name,'*.csv'));

creates structure named 'files'. Inside the structure 'files' there is a 'files.name' which has the assigned string 'test.csv', which is the file that I want to open.

But in the next step the command

[fid(i),msg]=fopen(files(i).name);

gives a message

No such file or directory

and frankly I cannot understand because it exists in the workspace!!

[Giorgos Papakonstantinou]

Another weird thing that I cannot explain happens when I use the command

[fid(i),msg]=fopen(files(i).name,'wt+');

In this case the fid takes a value different from -1 and the subsequent fopen command can be executed but then files.values is empty!!

[Giorgos Papakonstantinou]

At last I have noticed that if I move the second code within the folder that csv files are contained then code does not exhibit any problem. All the numerical values are contained in files.values structure.

[Kostas Chatzimpaloglou]

have found a solution to this problem?

[Walter Roberson]

[fid(i),msg]=fopen(files(i).name);

should be

[fid(i),msg]=fopen( fullfile(folder_name, files(i).name));

Answer 3

[Giorgos Papakonstantinou]

Ok solved myself. The problem was that I was using textscan outside the current folder. Therefore I changed the folder to the folder of interest and back to the initial folder.

str='C:\Users\user\Measurements\Test';
folder_name=uigetdir(str);
files=dir(fullfile(folder_name,'*.csv'));
curr_folder=pwd;
cd(folder_name);

for i=1:length(files)
   [fid(i),msg]=fopen(files(i).name);
    disp(msg);
    files(i).values=textscan(fid(i), '%f %f','delimiter',',',...
        'Headerlines',20,...
        'MultipleDelimsAsOne',1);
    fclose(fid(i));
end
cd(curr_folder)

[Stephen23]

Using cd should be avoided in code.

Using absolute/relative filenames is more efficient, robust, simple, and easier to debug, e.g.:

D = 'C:\Users\user\Measurements\Test';
S = dir(fullfile(D,'*.csv'));
for k = 1:numel(S)
    F = fullfile(D,S(k).name);
    [fid,msg] = fopen(F,'rt');
    assert(fid>=3,msg)
    S(k).values = textscan(fid,...);
    fclose(fid);
end