MATLAB: Error using fprintf Invalid file identifier. Use fopen to generate a valid file identifier.

errorfprintf

Hello, I have a problem, every program I try to run gives me this error. Even with the matlab examples.

This is the code from the mathworks page:

A = magic(4);
fileID = fopen('myfile.txt','w');
nbytes = fprintf(fileID,'%5d %5d %5d %5d\n',A);
fclose(fileID);
type('myfile.txt')

Best Answer

When fopen fails, it does not generate an error message. Instead, it sets the fileID to -1.

Check the value of fileID after calling fopen.

If it is -1, check whether you have write permissions in the directory you are trying to write to. Most likely you are trying to write a file to a directory that is read-only, and you either need to change directories or specify an absolute path instead of a relative path.

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MATLAB: Problem with fscanf command in creating .txt file

    filename1 = ['*new.txt'];%filename

    fid_t=fopen(filename1,'r')

This cannot work: '*new.txt' is not a valid file name, because the * is not allowed.

fid_p = fopen('final.txt','w'); % writing file id
if fid_p < 0, error('Cannot open file for writing.'); end
x = dir ('*new.txt');
for i = 1:length(x)
    filename1 = x(i).name;  %filename
    fid_t = fopen(filename1, 'r');%open it and pass id to fscanf (reading file id)
    if fid_t < 0, error('Cannot open file for reading.'); end
    data = fread(fid_t, inf, '*char');%read data
    fwrite(fid_p, data, 'char');%print data in File_all
    fclose(fid_t);% close reading file id
    fprintf(fid_p,'\n');%add newline
end
fclose(fid_p); %close writing file id

This take the file name from the list of files in x. In addition it uses FREAD and FRWITE, because it is faster to access the files in binary mode.

Never use FOPEN without testing the success.

Working with relative paths is less reliable than absolute path names:

Folder = 'C:\Your\Folder';
FileList  = dir (fullfile(Folder, '*new.txt'));
for iFile = 1:numel(FileList)
    FileName = fullfile(Folder, FileList(iFile).name);
    ...
end

MATLAB: Error using fprintf Invalid file identifier. Use fopen to generate a valid file identifier.

       directory: 1

That tells us that you have named a folder (directory) rather than a file or device name.

      GroupRead: NaN

That tells us that you are using MS WIndows rather than MacOS or Linux.

On MS Windows, it is not permitted to fopen() a directory.

(It is not permitted on MacOS either, but historically it used to be possible on old versions of Unix; you would get out the internal binary representation of the directory.)

You will need to change your path so that you are naming a file rather than a directory.

Best Answer

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MATLAB: Problem with fscanf command in creating .txt file

MATLAB: Error using fprintf Invalid file identifier. Use fopen to generate a valid file identifier.

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