MATLAB is a high-performance programming language used for technical computing as well as machine learning. When you are working with Matlab, you may experience the error “invalid file identifier. use fopen to generate a valid file identifier”.
Let’s check out how the error shows up
How the error occurs
When you are trying to use the Matlab script, you end up with the following error message:
Invalid file identifier. Use fopen to generate a valid file identifier.It happens when Matlab is not allowed to write and read on a specified file as a result of failed fopen.
How To Handle the Error “invalid file identifier. use fopen to generate a valid file identifier”
We have a few short and effective ideas to help you resolve the error. Check out the ideas
Idea 1
The error can be fixed if you include a permission option to fopen. The syntax for fopen is:
fileID = fopen(filename,permission)Here, a few possible permissions include ‘r’(default), | ‘w’ | ‘a’ | ‘r+’ | ‘w+’ | ‘a+’ | …
Where ‘r’ – reading by open file
‘w’ – Opening or creating a new file for writing. It removes all the contents if existing.
‘a’ – Also creates or opens a new file for writing. It appends your data to the file’s end.
‘r+’ – To read and write the file opened.
‘w+’ – Opening or creating a new file to read and write along with discarding all the contents that existed.
‘a+’ – Just like ‘a’, it also reads and writes by creating or opening a new file along with appending data to the file’s end.
…
In the case you are using fopen with no permission or with ‘r’ (default), you will get -1 as a result of fopen, which is itself an error. Using the below can fix the error:
fid=fopen('tmp.txt', 'w');
fid=fopen('tmp.txt', 'a');Idea 2
The fopen has the output fid (file identifier), which is an integer without being a permanent one. It is required to use open in order to obtain fid. Using incorrect fid in a few I/O commands related to files like fclose, fread, or fscanf. If fopen is not correct, you get -1 fid. In case of successful fopen, you get fid output 3 or even an integer greater than that.
Though, it is not possible to figure out the cause and place of the error when there is no code. The simple idea is to use a Matlab debugger to code from fopen (run program after setting up the breaking point) that is relevant using a single-step till fclose that is relevant to check whether fid (any variable name for fid you use) or some other data structure for file identifiers (if you are having more than one fid in the code) that changes between fopen and fclose in any point.
Conclusion
We shared two ideas to get rid of the error warning “invalid file identifier. use fopen to generate a valid file identifier”. I hope you like it and find it informative.
I wish you a happy error-solving!