Why dir function is creating additional files while creating a structure? how to ignore it?

Im trying to make a loop that reading all the files in a choosen folder, I use the dir function to make list of the names of the files and to iterate this list:

files = dir('folder');
for k =1:length(files)
    I = imread(files(k).name);

But there is always an error:

    Error using imread (line 347)
Cannot open file "." for reading. You might not have read permission.

When I open my structure named "files" there is 2 new rows that the dir function creates in addition to all the other files in that structure:

the first file named '.' and the second '..', those files not exist in the original folder, what to do to erase them or ignore them permanently?

Answer 1

[Catalytic]

Do a more specific search, like

files = dir('folder/*.jpg');

Or, just throw the first 2 away

files = dir('folder');
files(1:2)=[];

[Stephen23]

"Or, just throw the first 2 away"

Do NOT do this. The files/folders are those returned by the OS, and the presence or specific location of . and .. is not guaranteed. This has been discussed many times on this forum. It is also easy to demonstrate: simply create some files with names starting with ! or ' (both perfectly valid characters for filenames on both Windows and Unix, and which sort before the . character), and you will see that . and .. are NOT the first names returned by dir:

>> mkdir('subdir')
>> fclose(fopen('subdir/!test.txt','wt'));
>> fclose(fopen('subdir/''test.txt','wt'));
>> fclose(fopen('subdir/_test.txt','wt'));
>> S = dir('subdir');
>> {S.name}
ans = 
    '!test.txt'    ''test.txt'    '.'    '..'    '_test.txt'

To write robust code, simply use setdiff or ismember to select or remove names:

>> setdiff({S.name},{'.','..'})
ans = 
    '!test.txt'    ''test.txt'    '_test.txt'

[Matt J]

Or, similar to what Stephen suggests,

Names=deblank(string(ls('folder')));
Names(Names=="." | Names=="..")=[];

for I =1:numel(Names)
    I = imread(Names{i});
    ...
end

Answer 2

[Steven Lord]

If you're calling imread on the output of dir, you probably want to first check that the entry you're trying to read isn't a directory. You can do this all at once using the isdir field of the struct array returned by dir.

D = dir();
numberOfEntriesPreTrim = numel(D);
D = D(~[D.isdir]);
numberOfEntriesPostTrim = numel(D);
numberOfDirectories = numberOfEntriesPreTrim-numberOfEntriesPostTrim;
for whichfile = 1:numberOfEntriesPostTrim
    fprintf('File %d is %s.\n', whichfile, D(whichfile).name)
end
fprintf('Printed %d of %d entries in pwd (%d are directories.)\n', ...
    numberOfEntriesPostTrim, numberOfEntriesPreTrim, numberOfDirectories);

Note that '.' and '..' are not printed by the fprintf statement. They were trimmed because they're directories, but they still count for the last fprintf statement.

I needed to wrap D.isdir in square brackets because it creates a comma-separated list. The square brackets concatenates all the elements of that list into a vector.

As for what . and .. are, on the operating systems on which MATLAB is currently supported they are the current directory and the parent directory, respectively.