Error using textscan Invalid file identifier. Use fopen to generate a valid file identifier

if true
  % code
end
[head,nw,wv,spec]=ReadOOIfile('/Users/elkel/Active','D02e1.txt')
% [head,nw,wv,lt]=ReadOOIfile(dirn,filename);
% read, smooth, cut to 300-700nm every 2nm, for OOI USB2000+ output spectra
% DATA:  dirn : scan file directory, such as 'C:\Scans\'
%        fname: scan file name 
% OUTPUT:
%   head: file name, 'date & time', integ. time, n averaged, boxcar
%     nw: points in scan    wv = wavelengths    spec = spectrum output
wv=(300:1:700)'; n=length(wv);
fnm=[D02e1.txt];
fid=fopen(fnm);
rd=textscan(fid,'%s',17,'whitespace','\n'); heads=rd{1};
% heads contains first 17 rows of file--OOI scan parameters
%   extract=date,  integration time,  averaged,  boxcar
rd=textscan(fid,'%f %f');
fclose(fid);

Hi, I'm trying to figure out why I get the above error code when using textscan. I think it's something to do with my specification of the filename (fnm) but I can't seem to get it to work - how should the filename be specified? Directories all seem fine so any help much appreciated.

Answer 1

[Mischa Kim]

Laura, use

 fnm = 'D02e1.txt';
 fid = fopen(fnm,'r');

The filename needs to be a string of characters.

[Laura]

Thanks for that, I'm afraid the error message is still coming up. My current folder and userpath are the same, is there anything else I might be missing?

[Mischa Kim]

Could you attach the entire code and .txt file? See paper clip logo.

Another thing you can try:

 fnm = 'D02e1.txt';
 fid = fopen(fnm,'r');
 if fid == -1
   error('Author:Function:OpenFile', 'Cannot open file: %s', fnm);
 end

which will result in an error msg if the file cannot be opened as expected.

[Laura]

Code attached.

[Laura]

Data file attached. Many thanks for your help.

[Mischa Kim]

There are a couple of things:

• Change the function definition to [head,nw,wv,spec]=ReadOOIfile() and remove the semi-colon. You could read the file name as a parameter, but then you would use [head,nw,wv,spec]=ReadOOIfile(fnm), and without hardcoding it inside the function.
• Replace fname by fnm in head=[fnm ' ''' datestr ''' ' IT ' ' AV ' ' BX]
• Comment out the two clear commands. In one instance you are clearing a variable which you later try to access.

Once you get all this changed it'll work.