I get Undefined function or variable eror but that veriable is in Workspace

I get under eror but that veriable is in Workspace

??? Error using ==> eval
  Undefined function or variable 'mn'.% but before using of eval, I defined 'mn' and now the 'mn' is in workspace

      Error in ==> LEDbar>pushbutton1_Callback at 346
      gathd=eval(MAXmatris);

    Error in ==> gui_mainfcn at 96
          feval(varargin{:});

Error in ==> LEDbar at 42
    gui_mainfcn(gui_State, varargin{:});

Error in ==>
@(hObject,eventdata)LEDbar('pushbutton1_Callback',hObject,eventdata,guidata(hObject))

??? Error while evaluating uicontrol Callback

but before using of eval, I defined 'mn' and now the 'mn' is in workspace.

I am really confused for what tells 'mn' is undefined.

any idea?

[mohammad]

I run this by a GUI (so eval('mn') is inside of gui function)

Answer 1

[Matt Fig]

When you say you define the variable in the workspace, which workspace are you talking about? Do you mean it is defined in the base workspace (the command line)? If so, then that variable is not visible inside the callback, which has its own workspace. You could use EVALIN('base',...) but this may not make your problem go away, depending on what you are trying to accomplish.

Why are you using EVAL in a callback anyway?

[mohammad]

Thanks Matt. Yes it's defined in base workspace. Before yoyr answer i have used t=eval(mn) (mn is string and varies in a loop). Now i use this evalin('base','t','mn'); but in another line I have exactly the same problem. I use evalin('base','p',op); but errors that op is not defined (however it's in base workspace). for what by using evalin, it errors the same for other line?!

[Matt Fig]

Now you are beginning to understand why the use of EVAL is not encouraged! What are you trying to do by using EVAL?

[mohammad]

Matt I must use that I have no other way. I described reasons here

http://www.mathworks.com/matlabcentral/answers/15574-convert-a-variable-string-to-data

Now, by using

t=[];
evalin('base','t',mn) (that you told)

the problem was solved and really thanks. But I have exactly the same problem with the next line. I use evalin('base','p',op); but errors that op is not defined (however it's in base workspace). for what by using evalin, it errors the same for other line?!

[mohammad]

Oh, OK by using t=evalin('base',mn); the problem now solved. Really thanks.