Character limit in using fwrite?

I have a char string that I am trying to write to a .NET file, which is somewhat similar to a .txt file. However, I've noticed that strings above a certain length (seems to be around 100 characters) return the error message

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

Strings under this length write to my file directory just fine.

This is my first time using these MATLAB data writing commands, so I'm just using the basic file writing commands right now:

clear fileID
fileID = fopen(text, 'w');
fwrite(fileID, text);
fclose(fileID);

where text is my character string. How can I resolve this issue for these longer char strings?

Also, two somewhat related questions, if you don't mind:

(1) how do I write this string to a particular file extension, like .NET?

(2) is there a way to specify a name for the file that I'm writing to?

Thanks!

Answer 1

[Image Analyst]

text is a built in function name. That could be your problem. Pick a different name, and use your actual string variable name instead of text.

What is fileID? Is it -1? If so, you were unable to write to the file, possibly because of permission denials or the disk is full or something else.

[Sam]

Thanks for the prompt response.

I had actually been using another string variable name specific to my purposes ( CRNTinput ); I just arbitrarily chose text as example.

fileID does indeed have a value of -1 in this case, and a value of 3 when the string is written successfully.

[Walter Roberson]

[fileID, errmsg] = fopen(CRNTinput, 'w');
if fileID < 0
  fprintf('The program complained about opening because: %s\n', errmsg)
else
  ...
end

[Image Analyst]

What is the folder? If you're in Windows 7, it's very picky about where you can write to, like, you can't do anything under the c:\Program Files folder.

[Sam]

Walter, the message I get using your diagnostic code is

The program complained about opening because: No such file or directory

And Image Analyst, I'm just working in my SkyDrive folder.

[Image Analyst]

I guess it does not think your network SkyDrive is currently connected to your computer. I can't help you since I don't use one.

[Walter Roberson]

Your connection to your SkyDrive folder appears to be unstable.

Consider writing to a file in a temporary directory, and later copying it to your SkyDrive. http://www.mathworks.com/help/matlab/import_export/creating-temporary-files.html

[Sam]

Why do shorter strings still write successfully, though? For instance, if say, CRNTinput = blah, the file is written successfully, whereas if CRNTinput = blahblahblah...(repeated many tens of times), the file cannot be written.

I do notice that the created file's name is simply the string itself, so maybe the issue is simply that I cannot save longer strings because there is a character limit on the file name lengths?

[Walter Roberson]

Yes, operating systems limit the path component of filenames, often to 127 or 255 characters. Skydrive may have different limits. You should use a different name for the files. You might want to use datestr() to construct the name.

   filename = ['test_', datestr(now, 'yyyymmddHHMMFFF')];
   fileID = fopen(filename, 'w');

[Sam]

Okay. Is there a way that I can manually specify the name of the file that I am creating within my code?

[Image Analyst]

Of course, that's what Walter did. I prefer to use sprintf(). And be sure to use fullfile() to prepend the folder onto your basefilename.

[Sam]

Oh, I see. Thanks! Last question: is there a way to specify the file extension that I want to save the written file to?

[Walter Roberson]

filename = ['test_', datestr(now, 'yyyymmddHHMMFFF'), '.txt'];

or equivalently,

filename = sprintf('test_%s.txt', datestr(now, 'yyyymmddHHMMFFF'));

[Sam]

Got it. Thanks very much for your help, Walter and Image Analyst!