How can I flush the output of disp in Matlab or Octave?

Question

I have a program in Octave that has a loop - running a function with various parameters, not something that I can turn into matrices. At the beginning of each iteration I print the current parameters using disp.

The first times I ran it I had a brazillion warnings, and then I also got these prints. Now that I cleaned them up, I no longer see them. My guess is that they're stuck in a buffer, and I'll see them when the program ends or the buffer fills.

Is there any way to force a flush of the print buffer so that I can see my prints?

Here's more, including info on paging: chemie.fu-berlin.de/chemnet/use/info/octave/octave_22.html — Nucular
– Nucular, Commented Jan 31, 2012 at 14:01

moastab · Accepted Answer · 2010-04-14 07:47:29Z

46

Use fflush(stdout) and/or fflush(stderr) to flush the buffer from disp().

answered Apr 14, 2010 at 7:47

moastab

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2 Comments

Andrew Janke Over a year ago

Out of curiosity, do you know if there's a Matlab equivalent to fflush()? I'd like to do the same thing, but I use Matlab, not Octave, and there's no fflush() function.

Arthur Hebert-Ryan Over a year ago

In MATLAB, use drawnow('update') to flush the output.

Arthur Hebert-Ryan · Accepted Answer · 2019-04-23 18:32:04Z

30

As mentioned by moastab, fflush(stdout) works for Octave.

In MATLAB, use drawnow('update') to flush the output.

MATLAB's drawnow function will be familiar to those who control the redrawing of graphical objects in MATLAB, but it applies to the stdout stderr buffers as well. The 'update' option is not required, but limits the flushing to non-graphical queues. This detail is merely implied in the drawnow() documentation; I have verified it to work on fprintf calls in a loop.

edited Apr 23, 2019 at 18:32

answered Nov 19, 2011 at 0:39

Arthur Hebert-Ryan

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Comments

Patrizio Bertoni · Accepted Answer · 2016-07-13 10:32:37Z

21

Octave: You can turn off buffering of output by calling more off.

This will disable pagination such that all output is sent directly to the screen.

edited Jul 13, 2016 at 10:32

Patrizio Bertoni

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answered Feb 2, 2012 at 12:21

Micke

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rink.attendant.6 · Accepted Answer · 2015-07-21 14:41:27Z

7

Put the following commands at the beginning of your section or your code:

page_screen_output(0);

page_output_immediately(1);

edited Jul 21, 2015 at 14:41

rink.attendant.6

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answered Jul 21, 2015 at 14:24

Charles Valente

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yuk · Accepted Answer · 2010-04-13 20:53:23Z

3

If I understand your question correctly, you can use diary function to dump all session output to a text file. diary on will start recording, and diary off will stop. diary filename will use filename instead of default "diary".

It is build -in function in both Octave and MATLAB. For more details see help diary.

Also you can increase Octave buffer size. On Windows you can do it in Octave Properties dialog from upper left corner menu.

edited Apr 13, 2010 at 20:53

answered Apr 13, 2010 at 20:44

yuk

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not2qubit · Accepted Answer · 2019-03-20 14:15:22Z

2

From here and elsewhere, there are at least 5 methods to get immediate output, in Octave.

Use one of the following:

%---------------------------
% Turn OFF output buffering
%---------------------------
more off                        % command & NOT shown in output
PAGER = "less"                  % built-in var - shown in output
page_screen_output = 0          % built-in var - shown in output
page_output_immediately = 1     % built-in var - shown in output
fflush(stdout)                  % Need to call after each "output" line

answered Mar 20, 2019 at 14:15

not2qubit

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mtrw · Accepted Answer · 2010-04-13 20:50:34Z

0

drawnow will cause graphs to update, I'm not sure if it works on the stdout pipe as well.

You might also convert your disp(...) statements to fprintf(stderr, ...), I think stderr is handled differently from stdout on Octave.

answered Apr 13, 2010 at 20:50

mtrw

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