How to clear persistent variables?

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?

Answer 1

[Yair Altman]

you can use

clear functionName

and all the persistent vars in that function will be cleared (set to [])

[Image Analyst]

I suppose if you had function1() and function2() that used persistent variables, and you were using GUIDE, then in the OutputFcn() (which gets run both on startup, and again on shutdown), you'd put these lines:

clear function1;
clear function2;

and then next time you run the program, and it enters either function1 or function2, they won't have any values from the prior run of the program still "leftover" in the persistent variables of those functions.

[will wehner]

Doesn't work.

[mcsefl]

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

[Vineeth Nair]

The clear function does not clear persistent variables in local or nested functions.

[Alexander Ryan]

So is there a way to clear persistent variables in local or nested functions?

[Gavriel Aminov]

@Alexander Ryan

yes, please see here:

https://www.mathworks.com/matlabcentral/answers/16799-best-method-to-clear-persistent-variables#comment_1247873

Answer 2

[TADA]

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

[Walter Roberson]

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.

[Dariusz Borkowski]

Confirmed. Real headache. The behavior of local functions with persistent variables is random.

[Shubham Baisthakur]

Can you please share the command syntax?

[Walter Roberson]

clear NAME

where NAME is the name of a file that contains the function with the persistent variable you want to clear, without file extension. For example

clear project17

for file project17.m

There is no way to clear selectively within a file.

[Shubham Baisthakur]

Thanks Walter!

This works

Answer 3

[will wehner]

%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?

[Image Analyst]

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

Answer 4

[sixwwwwww]

you can use:

clear YourVariableName

see for more information:

http://www.mathworks.com/help/matlab/ref/clear.html

[Daniel]

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]

Maybe you can try the following commands:

Vars=whos;
PersistentVars=Vars([Vars.persistent]);
PersistentVarNames={PersistentVars.name};
clear(PersistentVarNames{:});

[will wehner]

Doesnt Work!

Answer 5

[morteza]

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

Answer 6

[Viktor Svensson]

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.