GUI table values to textfile - Cannot find a solution

I wanna save a cell array created in the opening function of a gui when the user clicks a save button in the gui. I am not able to do this. Here is my code, please tell me what lines to add to successsfully save the variables PPM, GFD and ESS into a single textfile as shown:

    function postprocess_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to postprocess (see VARARGIN)
Fg = varargin{1};
Ug = varargin{2};
eps = varargin{3};
sig = varargin{4};
elems = varargin{5};
L = varargin{6};
A = varargin{7};
E = varargin{8};
i=1:3;
PPM=[i.',elems(i,1:2),L(i,1),A(i,1),E(i,1)];
j=1:6;
GFD=[j.',Fg(j,1),Ug(j,1)];
k=1:3;
ESS=[k.',eps(k,1),sig(k,1)];
set(handles.uitable1,'Data',PPM);
set(handles.uitable4,'Data',GFD);
set(handles.uitable6,'Data',ESS);
% Choose default command line output for postprocess
handles.output = hObject;
% Update handles structure
guidata(hObject, handles);

and MY CALL BACK FUNCTION IS:

function savebutton_Callback(hObject, eventdata, handles)
% hObject    handle to savebutton (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
[filename, pathname] = uiputfile({'*.txt';'*.*'}, 'Save as');
if isequal(filename,0) || isequal(pathname,0)
 disp('User selected Cancel')
else
 disp(['User selected ',fullfile(pathname,filename)])
 path_file=fullfile(pathname,filename)
a=fopen(path_file,'wt');
fclose('all')
if filename < 0
error('Failed to open file "%s" because "%s" was not given name:', filename, msg);
end 
  ppmout=cell2table(get(handles.PPM,'Data'));
  writetable(ppmout, path_file);
end

I am going through several problems but mainly issues like "Reference to non-existent field 'PPM'" and also that when I try to write stuff from the uitable into text file, it generates error saying 'cannot "write" from a table of type double' while using writetable()

[Jan]

Please post the failing code and a complete copy of the error message. A shorter rephrased version is less useful.

Answer 1

[Jan]

Avoid "fclose(all)" but close the specific file directly by fclose(a).

"if filename < 0" is not meaningful here. What is its purpose?

The error message is clear: The struct handles does not contain the field "PPM". Perhaps you want to defined it in the OpeningFcn:

handles.PPM=[i.',elems(i,1:2),L(i,1),A(i,1),E(i,1)];