The invalid file identifier. use fopen to generate a valid file identifier error: what should you do?

Question

Hi everyone, I'm learning about matlab. While working, I try undefined. As a result, I get the message:

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

What can I do about the “invalid file identifier. use fopen to generate a valid file identifier” issue? Is there a better approach?

lyytutoria · Accepted Answer

The cause: fopen is fail because MATLAB is not permitted to read/write on the file you have specified. Therefore, the error appears. Solution: This error will disappear if fopen is added permissions. You can see in http://www.mathworks.se/help/matlab/ref/fopen.html , the fopen syntax is:

fileID = fopen(filename,permission)

'r' (default) | 'w' | 'a' | 'r+' | 'w+' | 'a+' | ... are some possible permissions and and below is their functions:

'r' – Opening a file for reading. 'w' – Opening or creating a new file for writing. Cutting the existing contents, if have. 'a' – Opening or creating a new file for writing. Adding data to the end of the file. 'r+' – Opening file for reading and writing. 'w+' – Opening or creating new file for reading and writing. Cutting existing contents, if have. 'a+' – Opening or creating new file for reading and writing. Adding data to the end of the file. ... If fopen is use with no permissions, or I use 'r' (default) option, fopen will return -1 value. It is an error. Then I use below commands and they give me success:

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

Raphaël Roy · Answer

fid (file identification) is fopen. It's the output of fopen. It is an integer that is not directly related to the file. To get fid, you will need fopen. You are probably using an incorrect fid (file identification) in a file-related I/O command such as fread or fscanf, or fclose. fopen that fails to succeed will give fid of the -1. Any valid file that has been successfully fopen will yield fid which is 3 or higher integer.

However, it is impossible to pinpoint the source of the error or bug without any code. You can use MATLAB to run the code one-by-one from fopen (set breakpoint and then run your program), until fclose. If fid (or any other variable you use for file identifiers) changes between fopen, fclose, or any data structure (if your code has more than one file identifier), it will be possible to see if that fid (or any other variable name you used for file identifiers) is affected.

Sign Up

Sign In

Forgot Password

ITtutoria Latest Questions

The invalid file identifier. use fopen to generate a valid file identifier error: what should you do?