how to write an opened file in a loop to a new file in a different folder using fwrite?

4 views (last 30 days)
Hi everyone,
I open a file in a loop using fopen. I make some modifications and then I want to write the file to a new folder but I get the error that the identifier is not valid.
Loop starts >
OpenFile = fopen('BetaWeatherFile.epw','r');
DuplicateATemporary = fopen('temporary.epw','w');
.....
modifications
.....
Then I want to use the fwrite here but it does not work.
"Error using fwrite Invalid file identifier. Use fopen to generate a valid file identifier."
  6 Comments
Jan
Jan on 10 Mar 2021
Yes, of course the first valid file identifier is 3. 1 is the standard output, 2 the channel for error messages.
With opening the file for reading by 'r', you cannot write to the file. Therefor your fwrite command replies 0 for: no character was written.
Are you sure you want to write the char vector 'E:\backup.epw' into the file? Maybe you have confused FWRITE and COPYFILE?

Sign in to comment.

Accepted Answer

Jan
Jan on 10 Mar 2021
Edited: Jan on 11 Mar 2021
Yes, of course the first valid file identifier is 3. 1 is the standard output, 2 the channel for error messages.
With opening the file for reading by 'r', you cannot write to the file. Therefor your fwrite command replies 0 for: no character was written.
Are you sure you want to write the char vector 'E:\backup.epw' into the file? Maybe you have confused FWRITE and COPYFILE?
FileName = fullfile(tempdir, 'test.txt')
OpenFile = fopen(FileName, 'w'); % [EDITED, typo fixed]
assert(OpenFile~=-1, 'Cannot open file for writing.')
fwrite(OpenFile, 'Hi', 'char')
fclose(OpenFile);
copyfile(FileName, fullfile(tempdir, 'test2.txt'))
  4 Comments
Jan
Jan on 11 Mar 2021
What do you expect as output of the copyfile command? It is a flag, which tells you if the copy was successful. I do not see a reason to store this in the variable CopyPhase .
Instead of copying the file, you could write directly to the wanted file. Then using an index in the file name is an obvious solution:
for k = 1:10
file = fullfile(Folder, sprintf('file%03d.txt', k));
...
end

Sign in to comment.

More Answers (0)

Categories

Find more on File Operations in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!