writing in a pre-existing txt file ?

Hello,

I have a question regarding writing my outputs to a pre-existing text file in a specific line

example :

in the text file I have the following :

A =

B =

I want my code to write the results next to A and B in the text file

The results will be ( for example ):

A = 1 2 3 4 5 6

B = 4 5 6 7 8 9

Can we do that in MATLAB ?

Thanks,

[Walter Roberson]

Note that it is not possible in any operating system MATLAB is supported on, to append text to a line, except by rewriting everything from that point to the end of file. Only the IBM MVS version of MATLAB (we are talking decades ago!) could put text on the end of a line, and only for files initialized a particular way; the mechanism involved each line being fixed length. DEC's VMS is the only operating system that MATLAB was ever been supported on that really supported inserting variable amounts of text to the end of a line without rewriting to end of file and without the lines being fixed length -- but for technical reasons, MATLAB never supported that particular kind of VMS file.

In all file systems and operating systems after the two I mention above, files are represented as streams of bytes, and the only way to add to a line is to copy the entire rest of file .

Answer 1

[Walter Roberson]

S = fileread('YourFile.txt');
parts = regexp(S, '\r?\n', 'split');
if isempty(parts{end}); parts(end) = []; end   %trailing newline
parts{1} = [parts{1} ' 1 2 3 4 5'];
parts{2} = [parts{2} ' 4 5 6 7 8'];

fid = fopen('NewFile.txt', 'wt');
fprintf('%s\n', parts{:});
fclose(fid);

It is not recommended that you write to the same file that is your input: if there were a problem in processing then you might have corrupted the original file.

As I discussed in January, it is not possible in any supported operating system to insert text at the end of a line without reading the entire rest of the file and rewriting it. All file systems on all systems supported by MATLAB are only streams of bytes that have no possible way to insert in place.

[Mahmoud Khadijeh]

Thank You Sir for your suggestions and feedbacks.

It works perfectly.

But I can't see the results in the new text file.

It appears only in the MATLAB command window.

Is this from the MATLAB version that I'm using?

[Walter Roberson]

Sorry,

fprintf('%s\n', parts{:});

should have been

fprintf(fid, '%s\n', parts{:});

[Mahmoud Khadijeh]

Thank You sir!

it works.

Regards,

Mahmoud

Answer 2

[Akira Agata]

Assuming the pre-existing text file is data.txt, how about the following?

cInput = readcell('data.txt','Delimiter','\n');

cAppend = {'1 2 3 4 5 6';'4 5 6 7 8 9'};

cOutput = strcat(cInput,cAppend);
writecell(cOutput,'data.txt')

[Mahmoud Khadijeh]

Hello,

Sorry for the late response.

When I tried this solution, I got the following error:

Undefined function or variable 'readcell'.

Could you please help me with that?

[Walter Roberson]

Did you edit the original question? Or do the files really only contain the text

A =
B =

and if they do contain only that, are there fixed numbers being appended? Or does the file contain the numbers?

Which MATLAB release are you using?

[Mahmoud Khadijeh]

Hello,

My question is the same. No need to modify it.

The text file contains in the first line A= and B= in the second line. So As you menioned, it looks like:

A=

B=

I want matlab to writie '1 2 3 4 5' next to A and '4 5 6 7 8 9' next to B. So it sould appear after running the code like this:

A= 1 2 3 4 5

B= 4 5 6 7 8

I'm using MATLAB 2016R2016a.

Best Regards,

Mahmoud

[Akira Agata]

Hi @Mahmoud Khadijeh,

The following error message you encountered is due to your MATLAB version (R2016a).

The readcell function has been introduced in R2019a.

> Undefined function or variable 'readcell'.

[Mahmoud Khadijeh]

No problem.

Thank you Sir