Invalid use of operator error - GUI

Hello, I keep getting an "invalid use of operator" error for line 293 below. I am not sure what the error is, since everything seems fine to me. Please lmk. The line is function pushbutton_start_Callback(hObject, eventdata, handles) towards the end of the code below. Please please help me!

function varargout = FlexSystemGUInew(varargin)
% FLEXSYSTEMGUINEW MATLAB code for FlexSystemGUInew.fig
%      FLEXSYSTEMGUINEW, by itself, creates a new FLEXSYSTEMGUINEW or raises the existing
%      singleton*.
%
%      H = FLEXSYSTEMGUINEW returns the handle to a new FLEXSYSTEMGUINEW or the handle to
%      the existing singleton*.
%
%      FLEXSYSTEMGUINEW('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in FLEXSYSTEMGUINEW.M with the given input arguments.
%
%      FLEXSYSTEMGUINEW('Property','Value',...) creates a new FLEXSYSTEMGUINEW or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before FlexSystemGUInew_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to FlexSystemGUInew_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES

% Edit the above text to modify the response to help FlexSystemGUInew

% Last Modified by GUIDE v2.5 27-Oct-2021 14:29:18

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @FlexSystemGUInew_OpeningFcn, ...
                   'gui_OutputFcn',  @FlexSystemGUInew_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT


% --- Executes just before FlexSystemGUInew is made visible.
function FlexSystemGUInew_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 FlexSystemGUInew (see VARARGIN)

% Choose default command line output for FlexSystemGUInew
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);

% UIWAIT makes FlexSystemGUInew wait for user response (see UIRESUME)
% uiwait(handles.figure1);

%% Serial Connection Settings                    
serialPorts=instrhwinfo('serial');
handles.nPorts=length(serialPorts.SerialPorts);
handles.serPorts = serialPorts.SerialPorts;

% Update handles structure
guidata(hObject, handles);

% --- Outputs from this function are returned to the command line.
function varargout = FlexSystemGUInew_OutputFcn(hObject, eventdata, handles) 
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;

% --- Executes on button press in Auto.
function pushbutton_auto_Callback(hObject, eventdata, handles)
% hObject    handle to Auto (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
%% Detector info
handles.d_num = get(handles.Detectors,'String');

%% Source info
handles.s_num = get(handles.Sources,'String');

%% Wavelength info
handles.wls = split(get(handles.Wavelengths,'String'));
handles.wls_num = length(handles.wls);

end
set(handles.pushbutton_start,'Enable','on')
guidata(hObject, handles);

% --- Executes on button press in pushbutton_SystemEnable.
function pushbutton_SystemEnable_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton_SystemEnable (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
connection = 'Serial';
if strcmp(get(hObject,'String'),'System Disable') % currently disconnected
    
    if strcmp(connection,'Serial') == 1
    serConn=serial(handles.serPorts{3}); %'COM4'
    set(serConn,'TimeOut', 3);
    set(serConn,'BaudRate',115200)
    set(serConn,'DataBits',8)
    set(serConn,'Parity','none')
    set(serConn,'FlowControl','none')
    set(serConn,'Terminator','LF');
    set(serConn,'StopBits',1);
    end
    
     try
        %Open selected serial port, enable button functions
        fopen(serConn);
        handles.serConn=serConn;
        %Send mode commands
        configStr=':I:0'; 
        fprintf(handles.serConn,'%s',configStr);
        pause(1);
        receiveText = fgets(handles.serConn);
        set(handles.text_IncomingText,'String',receiveText)
        set(handles.pushbutton_start,'Enable','on')
        set(hObject,'String','System Enable')
        handles.filePath = 0;
     catch e
         errordlg(e.message);
     end
else % Disconnect after connecting
    set(hObject,'String','System Disable')
    set(handles.pushbutton_start,'Enable','off')
    set(handles.text_IncomingText,'String','')
    fclose(handles.serConn);
    fclose(instrfind);
    instrreset;
end
guidata(hObject, handles);

function Background_CloseRequestFcn(hObject, eventdata, handles)
if strcmp(get(handles.pushbutton_SystemEnable,'String'),'SystemDisable') % currently connected
    fclose(handles.serConn);
    fclose(instrfind);
    instrreset;
end
delete(hObject);

pushbutton_start_Callback(hObject, eventdata, handles)

function edit_detectors_Callback(hObject, eventdata, handles)
% hObject    handle to edit_detectors (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_detectors as text
%        str2double(get(hObject,'String')) returns contents of edit_detectors as a double


% --- Executes during object creation, after setting all properties.
function edit_detectors_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_detectors (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function edit_sources_Callback(hObject, eventdata, handles)
% hObject    handle to edit_sources (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_sources as text
%        str2double(get(hObject,'String')) returns contents of edit_sources as a double


% --- Executes during object creation, after setting all properties.
function edit_sources_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_sources (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function edit_patch_Callback(hObject, eventdata, handles)
% hObject    handle to edit_patch (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_patch as text
%        str2double(get(hObject,'String')) returns contents of edit_patch as a double


% --- Executes during object creation, after setting all properties.
function edit_patch_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_patch (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function edit_wavelengths_Callback(hObject, eventdata, handles)
% hObject    handle to edit_wavelengths (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_wavelengths as text
%        str2double(get(hObject,'String')) returns contents of edit_wavelengths as a double


% --- Executes during object creation, after setting all properties.
function edit_wavelengths_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_wavelengths (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function edit_gain_Callback(hObject, eventdata, handles)
% hObject    handle to edit_gain (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_gain as text
%        str2double(get(hObject,'String')) returns contents of edit_gain as a double


% --- Executes during object creation, after setting all properties.
function edit_gain_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_gain (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function edit_repeat_Callback(hObject, eventdata, handles)
% hObject    handle to edit_repeat (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_repeat as text
%        str2double(get(hObject,'String')) returns contents of edit_repeat as a double


% --- Executes during object creation, after setting all properties.
function edit_repeat_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_repeat (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end

% --- Executes on button press in pushbutton_start.
function pushbutton_start_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton_start (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

function pushbutton_start_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_intensityR (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function edit_intensityR_Callback(hObject, eventdata, handles)
% hObject    handle to edit_intensityR (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_intensityR as text
%        str2double(get(hObject,'String')) returns contents of edit_intensityR as a double


% --- Executes during object creation, after setting all properties.
function edit_intensityR_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_intensityR (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function edit_intensityG_Callback(hObject, eventdata, handles)
% hObject    handle to edit_intensityG (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_intensityG as text
%        str2double(get(hObject,'String')) returns contents of edit_intensityG as a double


% --- Executes during object creation, after setting all properties.
function edit_intensityG_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_intensityG (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end



function edit_intensityB_Callback(hObject, eventdata, handles)
% hObject    handle to edit_intensityB (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit_intensityB as text
%        str2double(get(hObject,'String')) returns contents of edit_intensityB as a double


% --- Executes during object creation, after setting all properties.
function edit_intensityB_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit_intensityB (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end


% --- Executes on button press in pushbutton_SendIntensity.
function pushbutton_SendIntensity_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton_SendIntensity (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
int_R = get(handles.edit_intensityR,'String');
int_G = get(handles.edit_intensityG,'String');
int_B = get(handles.edit_intensityB,'String');

configStr = sprintf(':$:%s:%s:%s',int_R,int_G,int_B);
fprintf(handles.serConn,'%s',configStr)
pause(0.5)
receiveText = fgets(handles.serConn);
set(handles.receivingText,'String',receiveText)

% --- Executes during object creation, after setting all properties.
function pushbutton_sendIntensity_CreateFcn(hObject, eventdata, handles)
% hObject    handle to Sources (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end

function frequency_axes_Createfcn(varargin)

[Walter Roberson]

This (probably) does not answer your question, but I notice you have

function Background_CloseRequestFcn(hObject, eventdata, handles)
if strcmp(get(handles.pushbutton_SystemEnable,'String'),'SystemDisable') % currently connected
    fclose(handles.serConn);
    fclose(instrfind);
    instrreset;
end
delete(hObject);

pushbutton_start_Callback(hObject, eventdata, handles)

Why is your code invoking the pushbutton start callback from within the Background_CloseRequestFcn ?

[Karim Khalid]

It was a typo. I still get the same error without it.

[Walter Roberson]

I am not sure yet why it is happening, but what is happening is that MATLAB thinks that all of those function definitions are nested functions that it just hasn't seen a matching end for. And then at some point it hits the limit on the number of times you can nest a function definition, and starts saying that you have a syntax error.

Answer 1

[Walter Roberson]

You have

% --- Executes on button press in Auto.
function pushbutton_auto_Callback(hObject, eventdata, handles)
% hObject    handle to Auto (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
%% Detector info
handles.d_num = get(handles.Detectors,'String');

%% Source info
handles.s_num = get(handles.Sources,'String');

%% Wavelength info
handles.wls = split(get(handles.Wavelengths,'String'));
handles.wls_num = length(handles.wls);

end
set(handles.pushbutton_start,'Enable','on')
guidata(hObject, handles);

Notice the end statement. MATLAB thinks that end is matching the function definition, and becomes convinced that you are defining nested functions all over the place.

[Steven Lord]

If any of the functions in a file end with an end then all the functions in the file must end with an end.

One tool to help identify this is smart indenting the code in the MATLAB Editor. When I do this the start of FlexSystemGUInew_OutputFcn (line 73) is indented at the same level as the body of FlexSystemGUInew_OpeningFcn (starting on line 48) and the starts of the functions get further and further indented as the file proceeds. By the time we get to frequency_axes_Createfcn that function definition line starts at column 109. The first function where Code Analyzer complains is pushbutton_start_Callback on line 293 and that starts at column 69.