Why i am getting this error message

function pushbutton1_Callback(hObject, eventdata, handles)

% hObject    handle to pushbutton1 (see GCBO)

% eventdata  reserved - to be defined in a future version of MATLAB

% handles    structure with handles and user data (see GUIDATA)

clc

s  =str2double(get(handles.edit1,'string'));

in =str2double(get(handles.edit2,'string'));

en =str2double(get(handles.edit3,'string'));

t=s:in:en;

y=eval(get(handles.edit4,'string'));    %line 181

figure(1)

plot(t,y)

title('Actual graph')

x=0;

y1 = zeros(1,(length(t)-1));    

for i=1:(length(t)-1)

      x=x+(y(1,i+1)*in);

      y1(1,i)=x;

end

t1=s:in:(en-in);

figure(2)

plot(t1,y1)

title('After Intregation')

[Christopher Wallace]

What is on line 181?

Please reformat the code in the question. It isn't possible to see where the lines end.

Answer 1

[OCDER]

The error you're getting is probably caused by an invalid/empty string in handles.edit4. And DON'T use eval, esepecially in a GUI's editable text!

 y = eval('')  
 Error: This statement is incomplete.

 y = eval(get(handles.edit4,'string')); %DON'T USE EVAL! Security Risk!
 %  What if handles.edit4.string = 'delete(every_file)' ? You'll lose a lot of files!

What are you "evaluating"? Give us an example and we'll provide a safer and faster alternative to eval.

[Robiul Ferdous]

i am evaluating , sin(2*pi*t)

what should i use instead of eval??

[Walter Roberson]

str2func() instead of eval() . This still leaves security risks though, so ideally you should validate that the expression is well formed and not a risk before you str2func()

[OCDER]

Try something like this instead of that eval line.

FullStr = get(handles.edit4, 'string');  %EX: sin(2*pi*t)
FuncStr = FullStr(1:find(FullStr == '(', 1)-1);
SafeStr = {'sin', 'cos', 'tan'}; %Select function names you are okay with
if ~ismember(FuncStr, SafeStr) 
    fprintf('"%s" is not a valid function. These are: ', FuncStr);
    fprintf(' "%s" ', SafeStr{:});
    fprintf('\n');
    return  %ends your callback function early
end

FuncHdl = str2func(['@(t) ' FullStr]);
try
    y = FuncHdl(t);
catch
    disp('Something is wrong with this function handle:')
    disp(FuncHdl);
    return
end

[Walter Roberson]

Perhaps

FuncStrs = regexp(FullStr, '\w+(?=\()', 'match');
if ~all(ismember(FuncStrs, SafeStr))

as this should allow for a mix of functions such as sin(3*x)-cos(x/pi)

[OCDER]

Thanks Walter, that's much more robust. And here's one more security check, in case someone uses a string like:

FullStr = 'sin(mkdir(''test''),t)'; %Sneaky security bypass

and if you cannot list every safe string possible.

UnsafeStr = {'delete', 'rmdir', 'mkdir', 'movefile', 'copyfile'};
if contains(FullStr, UnsafeStr)
    fprintf('Detected an unsafe string! Cannot have: \n');
    fprintf(' "%s" ', UnsafeStr{:});
    fprintf('\n');
    return
end

There might be safer ways...

[Walter Roberson]

My suggestion already handles the nested calls

The rule for computer security is to never count on blacklists, as someone might find a clever way of encoding around the blacklist. For example systems that checked input text for ` specifically often failed to check percent encoding %60 or unicode %u0060 or HTML entities `

[OCDER]

I see. This clears up the blacklist vs whitelist approach. The other issue was what if the whitelist wasn't so obvious or is large? EX:

tanh(t) + sech(t) + ... more trig func

One way to get a larger whitelist would be:

SafeStr = arrayfun(@(x) strrep(x.name, '.m', ''), dir(fullfile(ctfroot, 'toolbox', 'matlab', 'elfun', '*.m')), 'un', 0)

Now more functions for trig are valid.

[Walter Roberson]

Interesting approach.

Though this does accidentally bring in the script 'Contents' (which is effectively just a help file script.)

Answer 2

[Robiul Ferdous]

how can i solve the error in matlab graphics internal fig file while evaluating ui control callback.

[OCDER]

The Answer is reserved for answer to your original question. If this is a new error and new question, post a new question. Otherwise, no one will try to respond here as an Answer was already accepted.

Post full error message in you new question post. Read this:

https://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer