Why do I keep getting an fopen error in my code? [absolute beginner]

My code is

filename = 'test02.txt';
outputtextfile = fullfile(output_dir, filename);
header = {'bad channels'};
f1 = fopen(outputtextfile,'w');
fprintf(f1,'%s\n',header{:});
fprintf(f1,'%d\n',removed_ch);
fclose(f1);

ERROR I get:

Error using fprintf

Invalid file identifier. Use fopen to generate a valid file identifier.

[Dyuman Joshi]

What are the values of outputtextfile and f1?

[Dani]

my workspace says the value of f1 is -1 and the value of outputtextfile is a 1x1 table containing my directory, i think

Answer 1

[Image Analyst]

This works fine:

output_dir = pwd
removed_ch = 9999;

filename = 'test02.txt';
outputtextfile = fullfile(output_dir, filename);
header = {'bad channels'};
f1 = fopen(outputtextfile,'w');
fprintf(f1,'%s\n',header{:});
fprintf(f1,'%d\n',removed_ch);
fclose(f1);

What is f1? Is it -1? That means you can't write there, like it's a readonly folder or a non-existent folder or something like that. Use isfolder to check if the folder exists.

Answer 2

[Walter Roberson]

outputtextfile = fullfile(output_dir, filename);

If outputtextfile were a table, then certainly fopen() would fail. However in order for it to be a table in that code, then fullfile() would have to have returned a table.

If you are using the MATLAB-supplied fullfile() then:

Error using fullfile

All inputs must be strings, character vectors, or cell arrays of character vectors.

(Which is not completely true: fullfile() will also accept numeric inputs and will char() them)

and given any of those, fullfile() cannot return a table() object.

So if you are getting a table object for outputtextfile then it follows that at that point in the code, fullfile is one of:

• a function handle pointing to something different than the MATLAB-supplied fullfile(); or
• the name of a user-supplied or third-party supplied function that is not the same as supplied by MATLAB; or
• is the name of a table() object that just happens to have a variable named 'test02.txt' and output_dir just happens to be a valid row number or row-name reference inside the table() object

... or possibly you are mistaken about outputtextfile being a table object at that point in the code.

[Walter Roberson]

Please note that if the directory named by output_dir does not exist, that fopen() will not create it.