What causes an invalid file identifier in MATLAB?

Question

I have a MATLAB script that I could have sworn worked fine the last time I used it (a year ago). Now, I get this error:

Invalid file identifier.  Use fopen         


        

Answer 1

I solved this problem for my self by adding permission option to fopen. As you see in http://www.mathworks.se/help/matlab/ref/fopen.html , fopen syntax is:

fileID = fopen(filename,permission)

Possible permissions, for example are: 'r' (default) | 'w' | 'a' | 'r+' | 'w+' | 'a+' | ...

'r' – Open file for reading.

'w' – Open or create new file for writing. Discard existing contents, if any.

'a' – Open or create new file for writing. Append data to the end of the file.

'r+' – Open file for reading and writing.

'w+' – Open or create new file for reading and writing. Discard existing contents, if any.

'a+' – Open or create new file for reading and writing. Append data to the end of the file.

...

If I use fopen without permission option, or if I use 'r' (default) option, fopen will return -1, which is error. I success with this:

fid=fopen('tmp.txt', 'w');
fid=fopen('tmp.txt', 'a');