MATLAB Answers

Daniel
3

How to clear persistent variables?

Asked by Daniel
on 5 Dec 2013
Latest activity Commented on by Walter Roberson
on 27 Apr 2019
I am currently using a persistent variable within a function that I would like to clear at the end of the execution of a larger program. I am currently using "clear functions". This is causing some headaches during debugging since this clears my breakpoints as well. Is there a way to clear only the persistent variables? Better yet, is there a way to clear specific persistent variables?

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6 Answers

回答者: Yair Altman
2013 年 12 月 5 日
編集済み: Yair Altman
2013 年 12 月 5 日
 採用された回答

you can use
clear functionName
and all the persistent vars in that function will be cleared (set to [])

  5 Comments

mcsefl
on 4 Dec 2015
My experience:
I found that "clear functionName" can in fact be used to clear persistent variables effectively.
However, I noticed a difference in behavior if it is used in a local function versus a function that is saved in a separate file. This approach does not seem to work if you are trying to clear a local function, if implemented as written above.
Here is minimal example to demonstrate the difference in behavior. The function "testFunc" is a local function, and there is an identical copy of testFunc that is saved in a separate file and re-named "testFunc_separateFile".
function clearTest()
clear testFunc
disp('testFunc output:')
for ii = 1:2
testFunc(ii)
end
clear testFunc_separateFile
disp('testFunc_separateFile output:')
for ii = 1:2
testFunc_separateFile(ii)
end
end
% Local Function
function testFunc(arg)
persistent counter
if isempty(counter)
counter = 0;
end
counter = counter + arg
end
If I run the "clearTest" twice, here is the output:
>> clearTest
testFunc output:
counter =
1
counter =
3
testFunc_separateFile output:
counter =
1
counter =
3
>> clearTest
testFunc output:
counter =
4
counter =
6
testFunc_separateFile output:
counter =
1
counter =
3
The clear function does not clear persistent variables in local or nested functions.
So is there a way to clear persistent variables in local or nested functions?

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回答者: will wehner 2014 年 1 月 8 日

%Example Function
function testCleanup
disp(' ')
k = 3;
myFun;
for i=1:2\n
myFun
end
function myFun
persistent x
if(isempty(x))
x=1;
disp('empty')
else
disp('not empty')
end
end
end %end testCleanup
The function myFun is called 3 times. Once, then 2 more times in a loop. When running this function for the first time it will display
empty
not empty
not empty
on each subsequent run of testCleanup, it displays
not empty
not empty
not empty
It is my desire to clear the persistent variable x at the end of the function testCleanup. Simply clearing the function does not work. Using the whos command outside the function scope does not work. Is there any way to use onCleanup to clear the persistent variable x?

  1 Comment

Try this:
function testCleanup
clc;
k = 3;
myFun;
for i=1:2
myFun
end
clear functions;
function myFun
persistent x
if(isempty(x))
x=1;
disp('empty')
else
disp('not empty')
end
end
end %end testCleanup

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回答者: sixwwwwww
2013 年 12 月 5 日

you can use:
clear YourVariableName
see for more information:

  3 Comments

Daniel
on 5 Dec 2013
Thanks for the response. Unfortunately, this does not work for persistent variables that are out of scope. For example, if you declare a persistent variable in a subfunction you cannot call clear from the base workspace to clear it.
sixwwwwww
on 5 Dec 2013
Maybe you can try the following commands:
Vars=whos;
PersistentVars=Vars([Vars.persistent]);
PersistentVarNames={PersistentVars.name};
clear(PersistentVarNames{:});
Doesnt Work!

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回答者: morteza
2015 年 1 月 23 日

you can use each of these instructions: clear all or clear classes or clear functions

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Answer by Viktor Svensson on 27 Jun 2016

Ran into this problem today, wanted to clear persistent variables and not the debug points. The best I could come up with was
debugStatus = dbstatus(fileName);
clear(fileName);
dbstop(debugStatus)
where dbstatus reads the debug points in the file and dbstop returns them after the clear.

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Answer by TADA
on 27 Apr 2019
Edited by TADA
on 27 Apr 2019

You can clear the name of the .m file in which that function is declared
it works for .m file functions, local functions, nested functions, class methods
it also works if you kept a function handle to that function

  1 Comment

Right. What you cannot do is clear persistent variables in an individual function declared inside a file. "clear" with a file name works by discarding the JIT structure for the file (which includes the persistent variables), but local and nested functions have their JIT as part of the enclosing file and cannot be individually cleared.

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