A Sprintf For Loop Breakdown

Hi all I am seeking assitance in understanding the following code and the sprintf statement!

I googled and youtubed this but still I don't get this can someone assist me, please?

I don't understand the sprintf what does the %3.3d.jpg do?

So far what I understanding is that this statement prints a minimum of 3 files but what does the %3.3d.jpg????!!!!??

Lastly the numFramesWritten1 = numFramesWritten1 + 1; What does the 1 do?!!!?? add 1 to every frame that is being written???

I don't get it!!!!???!!

Please help!

My code:

% Deploying For Loop To Traverse & Process From Frame '1' To 'last' Frame
    for t = 1 : numFrames1
        currFrame1 = read(filename1, t);    % Reading Individual Frames
        opBaseFileName1 = sprintf('%3.3d.jpg', t);
        opFullFileName1 = fullfile(Violence3, opBaseFileName1);
        imwrite(currFrame1, opFullFileName1, 'jpg');   % Saving Frames As 'jpg' Files
        Indicating Current Progress Of Files/Frames Written
        %Writing the minimum digits to be printed using 4decimal notations signed
        progIndication1 = sprintf('Writing Frame %4d of %d.', t, numFrames1);
        disp(progIndication1);
        numFramesWritten1 = numFramesWritten1 + 1;
    end 

Answer 1

[Stephen Cobeldick]

"I don't understand the sprintf what does the %3.3d.jpg do"

It is confusing because that formatting string uses undocumented behavior of sprintf.

Do NOT learn from that format string! (except perhaps how NOT to write format strings).

A naive interpretation of that format string might be

'%3.3d.jpg'
 %           start of formatting operator
  3          field width (min three characters)
   .3        precision (makes no sense with 'd' conversion type or an integer value)
     d       conversion type (signed integer)
      .jpg   literal string '.jpg'

So we would expect this to print a string with minimum characters, but obviously requesting three fractional digits from an integer is absolute nonsense, and so the string is actually parsed like this:

'%3.3d.jpg'
 %           start of formatting operator
  3          field width (min three characters)
   .3        number of digits including leading zeros (not documented!)
     d       conversion type (signed integer)
      .jpg   literal string '.jpg'
 

You can see this undocumented behavior with a few simple examples, e.g. a fieldwidth of 5:

>> sprintf('X%5.3d.jpg',7) % added 'X' to show the leading spaces
ans =
X  007.jpg

The proper, documented way to generate a string with leading zeros is like this:

>> sprintf('X%03d.jpg',7) % added 'X' to show leading spaces (i.e. none)
ans =
X007.jpg

[Matpar]

Hi Stephen Cobeldick,

Thank you so much, Understood! this was cofusing the hell out of me!!

I got it thanx!