MATLAB: Odd behavior combining sprintf and fprintf

Question

When I create a formatted string using sprintf and then print it to screen using fprintf, I am getting some odd behavior when the formatted string contains the '%' character. Example:

fprintf( sprintf( '%% \n' ) );

displays nothing on my screen. I can disp the formatted string and get the expected output, or print to screen directly by formatting the string with fprintf and get the expected output. I've tested this on OS X and Linux and I see the same behavior.

The problem is that I build a formatted string using sprintf and grab it's length to overwrite it later, and then I want to print to screen using fprintf, but when I do I lose my '%' characters. I'm not using disp because it doesn't appear to be printing exactly what's in the formatted string.

Any thoughts on what I'm doing wrong, or what I can do differently? Thanks for your help.

Answer 1

Try

fprintf(sprintf('%%%%\n'))

In order to print a % with the fprintf command, you have give the function two %-characters:

fprintf('%%')

The same is true for the sprintf-command. So sprintf turns two %-characters into one, and as you need two for fprintf, your string has to contain four %-characters.