MATLAB: Character limit in using fwrite

charfopenfwritelengthstring

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!

Best Answer

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.

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It's never a good idea to modify the matlab path (with addpath or others) just to read or write data files.

The simplest way to make sure that a file is read or written in the correct folder is to simply specify the folder as part of the name when you read/write. It's easy to do: use fullfile. You've done exactly that for your dir call. Why didn't you do the same for your fopen calls.

On a completely unrelated subject, matfiles is a fairly good variable name (dircontent may be better), FileName is also a good variable name, it's easy to understand what the variables contains. B is a horrendous variable name. It's also completely pointless in your code, it's unclear why you couldn't just have done

FileName = matfiles(i).name;

and not bother with the B or even better, keep using matfiles(i).name everywhere.

So, in the end:

testfiledir = 'E:\Data\Test\X';  %assuming it's both the input and output directory
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for i = 1:numel(matfiles)
Data = fileread(fullfile(testfiledir, matfiles(i).name));
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fclose(FID);

While you could also use readmatrix or readtable as suggested, it may change other formatting of the file and will be slower than the above due to the parsing it does.

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    filename1 = ['*new.txt'];%filename

    fid_t=fopen(filename1,'r')

This cannot work: '*new.txt' is not a valid file name, because the * is not allowed.

fid_p = fopen('final.txt','w'); % writing file id
if fid_p < 0, error('Cannot open file for writing.'); end
x = dir ('*new.txt');
for i = 1:length(x)
    filename1 = x(i).name;  %filename
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    if fid_t < 0, error('Cannot open file for reading.'); end
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    fwrite(fid_p, data, 'char');%print data in File_all
    fclose(fid_t);% close reading file id
    fprintf(fid_p,'\n');%add newline
end
fclose(fid_p); %close writing file id

This take the file name from the list of files in x. In addition it uses FREAD and FRWITE, because it is faster to access the files in binary mode.

Never use FOPEN without testing the success.

Working with relative paths is less reliable than absolute path names:

Folder = 'C:\Your\Folder';
FileList  = dir (fullfile(Folder, '*new.txt'));
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Best Answer

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