fprintf with warning of a lone trailing backslash

Hi,

I have used matlab earlier but forgotten most of it. I have a bunch of scripts from earlier co-workers and there is some warnings. Probably because the code is from 2015-2017.

This code produces a warning 'A lone trailing backslash, ' \ ', is not a valid control character.

for m = 1:M

folderName = strcat(rootFolder,timeSteps(m+2).name,filesep);

fprintf(['\nProcessing folder', folderName]);

As I am 'new' to this it is hard for me to understand how I should fix it. I assumed the problem is '\n..', so I tried to remove that but I still get the warning and I am not sure what removing the \n does in this case. The script seems to work anyway, but I would like to know what is wrong.

Hope someone can help me

Answer 1

[Image Analyst]

Like @Walter Roberson said, use fullfile, not strcat.

folderName = fullfile(rootFolder, timeSteps(m+2).name);
fprintf('Processing folder #%d of %d : "%s".\n', m, M, folderName);

Also see attached demo if you want to scan subfolders and do something to files in each subfolder.

[Andreas]

Yes! This solution is best. Thanks a lot for suggesting fullfile and not strcat. Thank you all for being helpfull!

Answer 2

[VBBV]

 folderName = strcat(rootFolder,filesep,timeSteps(m+2).name);
    fprintf(['\nProcessing folder %s', folderName]);

You need to interchange the filesep position to middle or center to distinguish names. Plus use the format specifier as well in fprintf

[Fangjun Jiang]

+1! filesep at the end of the string is the root cause of the warning!

[Andreas]

I tried changing filesep. That gives me an error:

'Processing folder ../output/\002Error using imread>get_full_filename (line 570)

File "../output/\002DEM.tif" does not exist.'

So this solution does not work.

The best solution so far is

 folderName = strcat(rootFolder,timeSteps(m+2).name, filesep);
    fprintf('\nProcessing folder %s', folderName);

Answer 3

[Fangjun Jiang]

Change to

fprintf(['\nProcessing folder %s', folderName]);

'\n' is fine, it produces a carriage return

Just need the '%s' to print the value of folderName.

[Les Beckham]

You need to remove the square brackets

[Andreas]

Hi,

Thanks for answering! I added %s but I still get the same warning message.

fprintf(['\nProcessing folder %s', folderName])

[Andreas]

Yes, Les Beckham, that worked! Thanks a lot!

[Fangjun Jiang]

Thank you @Les Beckham for your sharp eye.

Now, since you pointed it out, I wonder why the warning. I ran the original code in R2022b, no warning.

[Fangjun Jiang]

@VBBV 's answer points to the root cause of the warning. It is the filesep ('\' in Windows) at the end of folderName.

So, for @Andreas, the true fix (with minimum change to the original code) should be this

folderName = strcat(rootFolder,filesep,timeSteps(m+2).name);
fprintf(['\nProcessing folder', folderName]);

[Walter Roberson]

We recommend that you use fullfile()

Answer 4

[Jasmine Dhaliwal]

(I know your question is already answered, but since they mentioned that there's %d and %s, I wanted to make sure you also knew that there is %f for float numbers instead of doubles (%d)! How it works: You can specify how many digits and how many decimals you want with something like %4.2f, where 4 indicates a field width of 4 digits and .2 indicates how many decimals you want! In my class we really mainly used %0.2f iirc, so I certainly looked up the literature on what the first digit (4, in this case) meant, because I couldn't quite remember what it meant. As it is, I really couldn't tell you what "field depth" is, but hopefully this is helpful to you anyhow!

[Walter Roberson]

the number before the % is the minimum field width. It is the target width for a column of numbers. The default is right jurisdiction within the column but the "-" flag requests left justification and the "0" flag requests zero padding on the left instead of space padding. The field will use more characters if necessary: it is common, for example, for people to forget to take into account the space for a negative sign.