how to check the input is a valid text file name when creating a function in matlab

To check if an input is a valid text file name in MATLAB, you can use the exist function to determine if the file exists and is a plain text file. Here's an example function that uses this approach:

main.m
function isValid = isValidTextFile(filename)
% Returns true if the input filename is a valid text file
% and false otherwise

% Check if the file exists
if exist(filename, 'file') ~= 2
    isValid = false;
    return;
end

% Check if the file is a plain text file
fid = fopen(filename);
if fid < 0
    isValid = false;
    return;
end
isText = isequal(fgetl(fid), -1);
fclose(fid);

isValid = isText;
end
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In this function, the exist function is used to check if the file exists by returning a non-zero value (2) if it does. Then, the fopen function is used to attempt to open the file for reading. If the file can't be opened, the function returns false. Otherwise, the fgetl function is used to read the first line of the file. If the result is -1, then the file is empty. If the result is a string, then the file is not empty. If the result is an empty string, then the file is a binary file. By comparing the result of fgetl to -1, the function determines if the file is a plain text file.