I get error, 'Error using fopen File identifier must be an integer-valued scalar of type double.'

This are my two first lines of code,

[filename, path] = uigetfile ('*.txt','Select input file name');
fid = fopen ([path, filename], 'r');

Those anyone know what might be causing this error to show up?

Answer 1

[Shivam]

Hi Luis,

From the information provided, I understand that you are encountering an error while using the uigetfile and fopen MATLAB functions.

The uigetfile basically opens a modal dialog box let you choose the specified file type (here, .txt). The error you are encountring is because the opened dialog box is being closed without selecting the file. Due to which, uigetfile returns 0 for both 'filename' and 'path'. This further causes fopen to open a non-existing file leading to the error mentioned.

You can follow the below workaround to handle the error scenario:

[filename, path] = uigetfile('*.txt', 'Select input file name');

% Check if the user canceled the file selection
if isequal(filename, 0) || isequal(path, 0)
    error('File selection canceled.');
else
    % Construct the full file path
    fullFilePath = fullfile(path, filename);
    
    % Open the file
    fid = fopen(fullFilePath, 'r');
    
    % Check if the file was opened successfully
    if fid == -1
        error('Failed to open file: %s', fullFilePath);
    else
        %
        % Do the operations with the opened file
        %
        fclose(fid); % close the file when done
    end
end

You can visit these documentations links as well to understand more about 'uigetfile' and 'fopen' function:

• https://www.mathworks.com/help/matlab/ref/uigetfile.html
• https://www.mathworks.com/help/matlab/ref/fopen.html

I hope it helps in resolving the issue.