Adding a header to a .txt file

I have a code right now where I ask the user to select the text file that has 3 columns of data. I am currently adding a timestamp and exporting the text file back out to the user... what I could use help on is adding a header to the top of the data. I don't know what commands to write in my code in order to do this. Any suggestions at all would be greatly appreciated!!

Answer 1

[Jürgen]

I am not 100% sure what you are trying to do but if you want to write to a text file, that is quite well explained in the help of Matlab with an example, see below,

if first you read your data ( 3 columns) to a matlab matrix then open a new text file, write the header with fprintf then add the data, also with fprintf ( see example below) finally close the file,

probably you can also first open the orginal txtfile and add the header before the data, but I do not know the command by heart, I know you can append txt using fprintf with "a"

hope this helps a bit

regards,J

% create a matrix y, with two rows
x = 0:0.1:1;
y = [x; exp(x)];

% open a file for writing
fid = fopen('exptable.txt', 'w');

% print a title, followed by a blank line
fprintf(fid, 'Exponential Function\n\n');

% print values in column order
% two values appear on each row of the file
fprintf(fid, '%f  %f\n', y);
fclose(fid);

Answer 2

[Walter Roberson]

There is no mechanism to insert into a file, only mechanisms to overwrite within a file and mechanisms to create new files.

Jürgen's suggestion of reading the data in, creating a new file, writing the header, and then writing the data, is a workable solution (provided the file fits into memory.) It could be followed by renaming the new file to the old name.

Also workable:

fidin = fopen('InputFile.txt', 'rt');
fidout = fopen('OutputFile.txt', 'wt');
fprintf(fidout, '%s\n', 'The Header Goes Here');
while true
  thisline = fgets(fidin);
  if ~ischar(thisline); break; end   %end of file
  fwrite(fidout, thisline);
end
fclose(fidout);
fclose(fidin);

And then rename the new file to the old one.