MATLAB: Fopen works fine in *.m but fails in compiled Matlab

MATLAB Compilertext file

I use something like:
            fpCSV = fopen(NameOfFile, 'rt');
            fgets(fpCSV);
            lineStr = fgets(fpCSV);
            fclose(fpCSV);
in my *.m file. It is actually buried in the method of a class that I wrote.
In interactive mode in Matlab, the script works great. I ran the Application Builder Tool and successfully compiled. However, when I run my application I get "Invalid file identifier" (see attached screenshot). How do I debug this?

Best Answer

One important rule when dealing with user input, filesystem or anything else that is external to your program is to always make sure that it conforms to your expectations. In your particular case, that means checking that the file is actually open, i.e. check the value of fpCSV after the fopen call.
Another good practice is to only deal with absolute paths instead of relying on the current folder. I strongly suspect that is your problem here. The current directory is probably not the same in your executable as it is in interactive mode, and the file simply isn't in that directory. So:
[NameOfFile, PathOfFile] = uigetfile('*.csv');
[fpCSV, errmsg] = fopen(fullfile(PathOfFile, NameOfFile), 'rt');
if fpCSV == -1
   error('failed to open file %s because %s', NameOfFile, errmsg);
end
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