Question: Is there a preferred way to debug functions in matlab?
If I all calculations in a script, then every variable is in the workspace and I can easily query them to find out what's not working right. However, if I use a function, then only my outputs are visible and I can't see what's going wrong. I understand there are ways of getting around this, but thusfar they seem to be more trouble than just making one, long ugly, script. So how do YOU debug functions in matlab? Is there a preferred/efficient way of doing this?
I always make sure to enable "Stop If Error" in the Breakpoints menu and if I want to debug a specific function I set a breakpoint at the first line in that function (or at the point of interest). Note that "clear all", which is common in the beginning of scripts deletes all break points. Use "clear variables" instead.
See MATLAB settings - stop if errors for more info on how to make the Stop If Error persist when you restart Matlab.
Related
I did a standalone application in Matlab and it works. The only problem is that when I launch the application, it takes time before start asking to the user some file (it is the first think the program has to do). The user does not understand if the program is working or not, since no message neither symbol of working progress appear on the screen.
My idea is to show a waitbar until the window asking the file to user appears.
How can I do this? is it possible to use the waitbar outside a loop?
The script starts as follow:
close all
clear all
[filename,pathname] = uigetfile({'*.xlsx'},'Opening File','C:\');
I don't know why, it takes time before open the window for choosing the file.
The time between launch and file selection input appearing is most likely due to the time it takes to load the MCR. You could add a splash screen to your compilation.
If the end user is running from a command line wrap your exe in a system/shell which writes to the command window that the application is starting.
Your issue is most likely the use of clear all. This makes MATLAB remove all variables (in scope, global and persistent), and compiled scripts from memory, forcing it to recompile and load everything again.
If your purpose is to clear all variables in the current scope, you should be able to increase the initial speed of your script by only running clear instead.
Even faster speed can be achieved if you specify which variables to clear using clear var1 var2 ...
As stated in MATLAB's FAQ,
1.3.3.1. Why, when I edit a function file in MATLAB, is the change not seen by MATLAB until everything is cleared or MATLAB is restarted?
When you write an M-file in MATLAB, you can either write a script or a
function. The difference is that a script is read from the disk and
parsed line by line each time it is called. A function is loaded into
RAM for execution. Because it is loaded into RAM, when you edit a
function, that change is not loaded into RAM until a call to the new
function is made.
To get MATLAB to recognize your edited function, type
clear functions to clear all functions, or
clear <function name> to clear just your function out of RAM.
This is a major pain when I'm developing a function & editing it repeatedly (I use an external editor most of the time). I was thinking of putting in a final line, at least during debug, like
clear(myfunc)
but I'm concerned about unwanted side effects. Does anyone know if there are any?
Further, I'd rather have a way to configure MATLAB so it doesn't automatically store called functions in RAM once the top-level function (i.e. the one called from the console) terminates. Is that even possible?
EDIT: I should mention that MATLAB's behavior is inconsistent. Sometimes my edits take effect once I save the m-file, other times they don't even if I'm editing with the MATLAB IDE editor window.
In all honesty MATLAB has a very powerful editor so you really should
be using it. It will make you life easier. (just an opinion)
Unless you are running the code by stepping through it no change to code will be run until the code is re-run (preferably with a cleared workspace).
clear(myfunc) will clear the variables created by that function in upto that point. You can add at the end of any function or script clear variableA variableB for all variables you want cleared at the end. This will give you control to only clear what you want. Once variables are cleared the only effect will be that if those variables are called again later in the code an error will occur since they no longer exist.
If your simply testing that particular function and want to save time by not calling inputs each time and want to clear the workspace and command window at the same time. You can add the following code just beneath the function definition.
If you leave the following code and call the function from another function or script, the code will be ignored as long as the inputs are available to it externally. Anything you add to the if statement will only occur when you call the function with no inputs doc nargin. You could add it to the top level function and you would simply press the run button or f5 without having to type in the command window to run the code.
function [ output1, output2 ] = blah( input1, input2 )
if nargin == 0
clc
clear all
%above two lines will clear the workspace and command window when you run
%the function
%define function inputs
%(optionally add the following to behave as if you inserted a breakpoint
%in the location just before the error occurred (great for debugging)
db stop if error
end
*you can also add a short-cut to snippets of code up in the top right of the MATLAB interface to clear the workspace etc when they are clicked.
Hackish* idea for this:
I'd rather have a way to configure MATLAB so it doesn't automatically store called functions in RAM once the top-level function (i.e. the one called from the console) terminates. Is that even possible?
* This is the sort of thing I might use, while advising others on why it is a bad idea, also probably uses undocumented (thus unreliable) things.
Specifically if your using an external editor I guess your going to have to click on the command window to run the function...
commandWindowHandle = ...
handle(com.mathworks.mde.desk.MLDesktop.getInstance.getClient('Command Window'...
.getComponent(0).getComponent(0).getComponent(0),'CallbackProperties');
commandWindowHandle.MouseClickedCallback = 'clear functions'
It doesn't clear the function definitions on exiting a function rather on clicking on the command window
note: the callback will not fire if a function is currently running
For a potentially more reliable but more wasteful version:
commandWindowHandle.KeyPressedCallback= 'clear functions'
will help* ensure definitions are clear, but is wasteful as every keystroke will run 'clear functions'... although after one keystroke this will be quicker as there will be no functions in memory!
* No guarantee I know there are ways in which this could fail... having at least 1 keystroke in the command window after the previous function call has finished would be advisable!
To disable these set the callback to empty string ''
commandWindowHandle.MouseClickedCallback = ''
commandWindowHandle.KeyPressedCallback= ''
This question already has answers here:
Stop and continue execution from debugger possible?
(6 answers)
Closed 8 years ago.
Strg+C stops and kills a Matlab script (at least sometimes). But is there a way to stop a Matlab, take a look at some variables and continue the calculation?
I am not talking about just setting a breakpoint. I want my script, let’s say run for couple hours come back to it hit some buttons that stops the calculations take a look at some variable and then continue the calculation.
I tried to find out if there is some shortcut key for this – I am quite sure there isn’t.
Now I was thinking about including an if-case that looks if a certain button was pressed by the user. If so there would be a useless k=0 line and a breakpoint on it. And if no one is pressing this button the loop would continue. But this is where my limited Matlab knowledge leaves me. I don’t know if there is a way to ask for a user-button press but don’t wait for a button press like in the function input. Also I just have a running script, I don’t have any GUI.
To drop to the command prompt you need the command keyboard and then type return when you have finished (you don't need a breakpoint). The tricky bit is how to trigger it. There a few options. The easiest is to open a figure window. The following code halts the process when any key is pressed.
keyDownListener=#(src,event) keyboard;
fig = figure;
drawnow
set(fig,'KeyPressFcn',keyDownListener)
for p=1:10000
%do some thing
end
You can modify this to test for a specific key since the keypress is contained within the event struct.
To use no figure gui at all its more of a problem. I'm not aware of a non blocking keyboard input method. A mex file the runs kbhit() in C might do it, but kbhit() is not standard C so it would only work on Windows. An easier option maybe to test for the presence of a file.
for p=1:100000
if exist(fullfile(pwd,'halt.tmp'),'file')
keyboard
end
%do something here
end
This drops to the debug console when halt.tmp is created in the current directory.
Other potential methods could involve using multiple threads to read 'input' (either the Parallel computer toolbox or undocumented Java code), or using http://psychtoolbox.org/ as mentioned by #bdecaf
I have recently started using MATLAB without GUI by starting matlab with -nodesktop option and it is considerably faster.
However presently I have no way to debug a .m script in non gui mode. I have to open the default matlab editor every time I have to debug.Has anyone figured out a way to do it?
Thanks in advance
I am using Ubuntu Linux, in case that helps.
To set breakpoints with the command line, dbstop is the tool (plus dbclear to clear breakpoints and dbstatus to list them).
There are presently 17 different forms to dbstop, which allow you to specify various combinations of:
The M-file in which to stop
Line number
Sub-function
Conditional to an arbitrary expression. For example,
dbstop in myFun.m at 224 if ~exist('x','var')
At any run-time error (dbstop if error)
At a specific error (e.g dbstop if error myFun.m:barErrorId)
At any warning (dbstop if warning) or specific warning
If NaN or Inf are encountered (dbstop if naninf)
See the documentation for dbstop for details and good examples.
Also get used to dbcont (or F5), dbstep (or F10), dbquit (Shift+F5), dbstep (also dbstep in, dbstep out), dbstack (to see where you are and how you got there). The keyboard shortcuts may be different outside of Windows.
Far less used, but still very useful are dbup and dbdown, which allow you to switch workspace context (memory stacks).
See the summary of functions and a list of examples and how-to pages in the MathWorks page on Debugging.
Related to the "db" functions is checkcode, which will check your code for possible problems before you even run it. This is a nice substitute for the red squiggly underlines that you would get in the MATLAB Editor.
Once you get a hang of dbstop and it's syntax, you won't often need to insert a keyboard into your code, but it's always an option.
Try placing the keyboard command in your code to insert a breakpoint. When the keyboard command is reached, MATLAB will drop into an interactive prompt that you can use to inspect variables. For example:
x = rand(10,10);
y = rand(10,5);
z = x * y;
keyboard; % you can interactively inspect x, y, z here
z = sort(z);
To leave keyboard mode, you can type dbquit to exit the program, or return to continue executing the program.
Another trick is to turn on dbstop if error which will automatically drop you into an interactive prompt whenever your code crashes.
You can use MATLAB -Dgdb if that helps. This sets gdb as the debugger. You will need to be familiar with gdb of course.
Once you do that, use the standard gdb commands to debug it.
EDIT
My mistake. Above won't work for M-Files. (Not having MATLAB to try things out is a pain :)
MATLAB has a pretty good set of debugging commands you can use from the commandline. If you insert keyboard commands in your MATLAB code, you can then use the commands.
You can use MATLAB's editor debug button to debug within MATLAB environment
This question already has answers here:
Stop and continue execution from debugger possible?
(6 answers)
Closed 6 years ago.
In MATLAB, I'm running some code which takes a while to run. I'd like to pause the code to check on some variable values. Is there a way I can do this without having to re-run the code from the beginning? I don't want to terminate the program; just pause it.
You can halt execution and give a command prompt in two ways of which I am aware:
Putting keyboard in your code where you want to stop.
Setting a breakpoint.
You can resume and stop execution with dbcont and dbquit, respectively. To step forward, use dbstep. dbstack lets you see where you are. There are many more commands. The help page for any of these will give you other suggestions.
As Dennis Jaheruddin has pointed out, dbstop also has several useful features worth trying. In particular is the ability to set conditional and global (any line meeting a criterion) breakpoints via the dbstop if syntax. For example, dbstop if error will break to a debugging command prompt on any error. One suggestion he made, which I now do, is to put dbstop if error into startup.m so that this behavior will be default when you start MATLAB. You may need to create this file in a userpath folder; edit(fullfile(regexp(userpath,'^[^;]*','match','once'),'startup.m')).
One way to achieve what you're looking for would be to use code sections (also known as code cells), where you divide your code into sections divided by lines with two percent signs (%%).
Then, in the editor, you can press ctrl+enter to execute the current code section, and ctrl+up/down to navigate between sections.
Well there is the pause command, but then you cannot check for the variable contents in the workspace because the program is running.
What you probably want is to set a breakpoint (See the Debug menu / key F12).
At a breakpoint matlab pauses the program and enters debugging mode in which you can see and edit the variables. Once finished, you can resume the program where it was paused.
I'm not sure about Windows users but if you're running Linux you can start Matlab in a terminal using
matlab -nodesktop
then once Matlab has started, cd to your project directory and start your Matlab script. Now whenever you want to pause execution you can use ctrl-Z. Then to resume type fg. I hope this helps.