how to delete a custom warning identifier, not just "display off" ?

I hope delete the custom warning identifier, but in Matlab, it seems like only hide it by setting state "off", however, the identifier is still there,how to actually remove the custom warning identifier

Answer 1

[Adam Danz]

> how to delete a custom warning identifier

If you want to permanently delete the custom warning ID so that it never appears anywhwere, find where the ID is defined and delete it from the file.

Suppressing a warning and removing it from lastwarn

When a specific warning is suppressed using warning(state,warnID), the warning is still picked up by lastwarn.

The syntax warning('') resets the warning state of lastwarn. Here's a demo that illustrate this behavior.

Throw a warning in MATLAB

A = eye(2);
B = [3 6; 4 8];
C = B\A; 

Warning: Matrix is singular to working precision.

lastwarn

ans = 'Matrix is singular to working precision.'

Clear the lastwarn state

warning('')
lastwarn

ans =

  0×0 empty char array

Produce the warning again

C = B\A;

Warning: Matrix is singular to working precision.

Now suppress this specific warning

warning('off','MATLAB:singularMatrix')

Show that the warning no longer appears

C = B\A;  % no warning 

Show that lastwarn still stores the warning

lastwarn

ans = 'Matrix is singular to working precision.'

The problem of using warning('')

The problem with using warning('') is that it will reset the lastwarn state no matter what the last warning is. Let's say MATLAB issued an important warning just before the line of code that produces the warning you'd like to suppress. If you call warning('') MATLAB will indicate that no warning was thrown at all.

Revert lastwarn instead of clearing it

If you want to suppress a specific warning and prevent lastwarn from returning the specific warning, you can store the lastwarn state before the warning appears and return the state after the section that would throw the warning. I use onCleanup to return the warning state.

Example

warning('Example warning')

Warning: Example warning

lastwarn

ans = 'Example warning'

% store the current lastwarn state
[lastw.msg, lastw.id] = lastwarn;

% suppress the specific warning
warning('off','MATLAB:singularMatrix')

% Ensure that the original warn state is returned
% when lastwarnCleanup is cleared
lastwarnCleanup = onCleanup(@() lastwarn(lastw.msg, lastw.id));

% Here's the code that normally throws the warning we suppressed.
% No warning is shown.
C = B\A;  % warning ID:  MATLAB:singularMatrix

% This line is optional but useful in a script.
clear lastwarnCleanup

Now test lastwarn. Notice that it does not return MATLAB:singularMatrix warning.

lastwarn

ans = 'Example warning'

Temporary warning suppression

Sometimes you may only want to suppress a warning locally within a function or script rather than for the entire MATLAB session. In those cases, you can use onCleanup to restore the initial warning state at the end of the function or when the cleanup object is deleted.

From the example above, instead of calling

warning('off','MATLAB:singularMatrix')

You can replace that line with this.

warnID = 'MATLAB:singularMatrix';
origState = warning('query', warnID);
cleanupWarningState = onCleanup(@()warning(origState)); 
warning('off', warnID)

which will revert to the original warning state after cleanupWarningState is cleared.

[Cheng Li]

Thanks a lots, the onCleanup method sounds a good idea. But I have created a new custom warning identifier by calling function warning with 2 argumets like warning('mytool:myidentifier','message') and I didn't change any original built-in warning identifier as well as its state, so I just want to delete the new custom warning identifier 'mytool:myidentifier'. And I find that it cannot be removed even if I restart Matlab software

[Adam Danz]

Let's see if I understand your description.

1. In some file or in multiple files you added the line warning('mytool:myidentifier','message').
2. Later you deleted those lines from all of the files and then saved the files.

After deleting those lines, where do you see mytool:myidentifier?

[Cheng Li]

Thanks a lot. Yes, I thought the configuration about all warning identifiers may be recorded in certain file since this identifier is still there after restarting Matlab, but when I searched among all files for the keyword 'identifier' in filename, I didn't find this specific file. Maybe I didn't say it clear. Actually, I didn't add the line warning('mytool:myidentifier','message') in any file, I just wrote this command in CLI, and the identifier was established. I don't see some lines about mytool:myidentifier in any file as possiblely as I can find, but in fact, I can query it by calling warning('query','mytool:myidentifier'), and this command returns its state is 'on' or 'off', depending on the former command warning('on/off','mytool:myidentifier'). Only if I query another string of identifier not to be defined yet, Matlab raises an error, saying the identifier is wrong. Hence, I think this identifier 'mytool:myidentifier' exists there in certain file. So, now the key is where this specific file containing all warning identifier information can be found, I don't know its name

[Steven Lord]

Only if I query another string of identifier not to be defined yet, Matlab raises an error, saying the identifier is wrong.

Can you show us the exact line of code you run to perform that query and the full and exact text of the error message you received? Show all the text displayed in red and/or orange in the Command Window. I want to make sure I understand the problem that you're describing correctly.

[Les Beckham]

I think that the default state for warnings is on. Thus warning('query', 'x:y') will return the The state of warning 'x:y' is 'on' for any character strings x and y as long as there is a colon between them. No matter whether you have previously actually issued such a warning using the warning function.

warning('query', 'mytool:myidentifier')

The state of warning 'mytool:myidentifier' is 'on'.

warning('query', 'x:y')

The state of warning 'x:y' is 'on'.

warning('query', 'z:t')

The state of warning 'z:t' is 'on'.

warning('query', 'x')

Error using warning
Unknown setting or incorrect message identifier 'x'.

[Cheng Li]

Yes,Thanks a lot, I mistook the identifier string, in fact I used 2 colons in strings as the other contrastive identifier. I thought as long as it'd contained a colon it could be an identifier. I should try more cases. So, why Matlab raises error is because the pattern of the contrastive identifier string is illegal. And it shows the same as you said that any legal warning identifier string can be queried out with the default state 'on'. Now, the problem is solved, thank you again

[Cheng Li]

Thank Adam Danz, Steven Lord, and Les Beckham for your time to answer, this problem is solved now

[Les Beckham]

You are quite welcome.

[Adam Danz]

Thanks for following up with your explanation, @Cheng Li!

Answer 2

[Walter Roberson]

lastwarn

ans =

  0×0 empty char array

warning('IEH754H GETMAIN cannot provide buffer')

Warning: IEH754H GETMAIN cannot provide buffer

lastwarn

ans = 'IEH754H GETMAIN cannot provide buffer'

warning('')
lastwarn

ans =

  0×0 empty char array

[Cheng Li]

Thank you, however, maybe you mistake what I mean. I hope to delete my defining warning identifier not only the warning message. warning identifier is like this pattern of "mytool:mytypes" as the bult-in warning identifier "MATLAB:singularMatrix" which comes out when the matrix A is close to be singular in equations Ax=b,but whose warning message is string "Matrix is singular to working precision." and is what the function 'lastwarn' returns. The warning identifier can be created by giving 2 arguments to warning(warnID,warnMsg),if the first argument is in format of "string:string", it will be regarded as the warning identifier, and the second as the warning message. And the custom warning identifier is so difficult to remove