"clear all" causing annoying warning messages

I am using "clear all" at the start of a ".m" file that I have written myself (lets call it "myfile.m"). When I run the file, I get three identical messages stating "Warning: The file 'myfile.m' could not be cleared because it contains MATLAB code that is currently executing." I don't want to turn warnings off, because I am writing my own warnings later in the file. Why does this happen and how can I prevent it? I am using Matlab version 2017a.

[KSSV]

Are you sure Clear all is placed only at the start of the code?

[Stephen23]

"clear all" causing annoying warning messages"

Putting clear all at the top of every script is one of the most common signs of cargo-cult programming in MATLAB. The best solution is: do not put clear all at the top of every mfile, and learn to write functions. Problem solved!

Search this forum to know more about why putting clear all everywhere is a bad practice (as you are starting to find out):

https://www.mathworks.com/matlabcentral/answers/272064-difference-between-clear-and-clear-all

https://www.mathworks.com/matlabcentral/answers/329964-how-to-clear-all-variables-of-a-workspace-except-for-those-explicitly-excluded

https://www.mathworks.com/matlabcentral/answers/43497-the-command-clc-and-clear-all-does-not-work-on-a-script-in-the-editor#answer_53402

https://www.mathworks.com/matlabcentral/answers/344338-clc-clear-all

https://www.mathworks.com/matlabcentral/answers/57361-hi-i-stuck-in-basics-of-matlab-function-command

https://www.mathworks.com/matlabcentral/answers/59375-can-i-use-2-push-buttons-to-start-and-stop-this-code-of-mine

http://blogs.mathworks.com/pick/2013/07/19/clear-everything/

https://www.mathworks.com/matlabcentral/answers/302898-what-do-you-think-of-did-you-mean-clearvars-except

etc, etc, etc.

Answer 1

[Jan]

clear all clears Matlab's memory in a brutal way. While removing all locally used variables might be useful for scripts, which are short hacks or prooves of concept, it is evil is productive code. Prefer clean workspaces by using functions instead.

Then clear all deletes all functions from the RAM, and the reloading from the slow hard disk wastes a lot of time. Doing this frequently means a massive loss of speed. In your case Matlab warns, that some functions cannot be removed. Perhaps they are callbacks of GUIs or timers, or the currently processed M-code.

In addition all persistent variables are cleared and many functions need a time-consuming re-initialization afterwards.

In older Matlab versions clear all has deleted all debugger breakpoints also, and anything, which impedes debugging is an enemy of teh programmer.

The solution is trivial: Omit the evil clear all. Instead of hiding the warning message, this is much more efficient.

[Sarah T]

Thank-you. I have replaced it with "clearvars" and this seems to work fine.

Answer 2

[David Cazenave]

You can still turn off the warnings, and then turn them back on before your 'custom warnings.' If that helps, Thank you ... Thank you very much.