Live script fprintf temporarily not printing whole line

While doing a bunch of file IO in a Live Script, and printing with fprintf, sometimes the line does not complete printing. Temporarily, it looks like the image below until the next iteration begins.

I was able to sort of recreate the effect with the code below, but what can be only a flicker in the execution of this snippet is much more noticable on my other project.

for i= 1:10
    fprintf("Hello %d\n",i)
    B= inv(rand(3000)+ 2*eye(3000));
end

Hello 1
Hello 2
Hello 3
Hello 4
Hello 5
Hello 6
Hello 7
Hello 8
Hello 9
Hello 10

Is this a bug or am I missing something?

[Walter Roberson]

This does not surprise me.

Output within Live Script is buffered. There are weird effects. For example

hold on
for i = 1 : 10
    plot(rand(1,5));
    fprintf("Hello\n");
end
plot(0.5,1,'*');

will display all of the text first and the plot at the end, but

hold on
for i = 1 : 10
    plot(rand(1,5));
    fprintf("Hello\n");
end

will display all except one of the text first, then the plot, then the last text.

[dpb]

Never use live script so no experience, but...I don't suppose a drawnow will make any difference here? Does disp act any differently?

Answer 1

[Jatin]

Hi @Zel Hurewitz,

I agree with what you mentioned, ‘fprintf’ does behave inconsistently in live editor. I’ve also faced the similar issue where the output of 'fprintf' is buffered.

For example,

for k = 1 : 10 
        fprintf('Hello: %d', k); 
        if k < 10 
             fprintf(","); 
        end
end 

Hello: 1

,

Hello: 2

,

Hello: 3

,

Hello: 4

,

Hello: 5

,

Hello: 6

,

Hello: 7

,

Hello: 8

,

Hello: 9

,

Hello: 10

This code adds a new line with 'fprintf' in live editor which is not seen in standard script, as a workaround to the issue, Kindly check if wrapping the code inside a function as below helps your cause.

fun(10) 

Hello: 1,Hello: 2,Hello: 3,Hello: 4,Hello: 5,Hello: 6,Hello: 7,Hello: 8,Hello: 9,Hello: 10

function fun(K) 
    for k = 1 : K 
        fprintf('Hello: %d', k); 
        if k < K 
             fprintf(","); 
        end
    end 
    fprintf("\n"); 
end

Kindly refer to the following MATLAB Answer to know more on how to resolve this issue:

https://www.mathworks.com/matlabcentral/answers/770853-inconsistent-behaviour-in-fprintf-output-scripts-and-livescripts?s_tid=answers_rc1-1_p1_Topic

Hope this helps!