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Why is empty string test failing?

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Ba Ba Black Sheep!
Ba Ba Black Sheep! 2017-4-20
评论： dpb 2017-4-21
.
This GUI's source code is giving me error message:
function browsePushButton_Callback(hObject, eventdata, handles)
% hObject handle to browsePushButton (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% show open file dialog
[filename, pathname] = uigetfile({ '*.jpg'; '*.png';'*.bmp';'*.jpeg'; }, ...
'Open image', ...
'' ...
);
% obtain image-file's path
imagePath = strcat(pathname, filename);
% this test is failing
if (imagePath ~= '')
image = imread(imagePath);
% digging out image related info
[pathstr,name,ext] = fileparts(filename) ;
fileinfo = imfinfo(imagePath);
FileSize1 = fileinfo.FileSize(1,1);
width = fileinfo.Width;
height = fileinfo.Height;
%
axes(handles.imagesPictureBox);
imshow(image);
else
h = msgbox('Invalid Value', 'Error','error');
end
Error message
Error using ~=
Matrix dimensions must agree.
Error in OpenFileDialogBoxTest>browsePushButton_Callback (line 91)
if (imagePath ~= '')
Error in gui_mainfcn (line 95)
feval(varargin{:});
Error in OpenFileDialogBoxTest (line 42)
gui_mainfcn(gui_State, varargin{:});
Error in @(hObject,eventdata)OpenFileDialogBoxTest('browsePushButton_Callback',
hObject,eventdata,guidata(hObject))
Error while evaluating UIControl Callback

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采纳的回答

dpb
dpb 2017-4-20
>> p=cd
p =
C:\ML_R2014b\work
>> whos p
Name Size Bytes Class Attributes
p 1x17 34 char
>> if p~=''
,disp('not empty'),end
Error using ~=
Matrix dimensions must agree.
>>
imagePath is an array of characters just as the variable p above; Matlab relational operators are vectorized and do a comparison element-by-element. Above you're trying to compare an array of length(imagePath) to an empty (zero-length) array so if there is anything in the variable the LH and RH lengths are incompatible; hence the error.
Use isempty instead, that's what it's for...
Example using above illustration...
>> p='';
>> isempty(p)
ans =
1
>> p=cd;
>> isempty(p)
ans =
0
>>
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dpb
dpb 2017-4-21
OK, so the comparison must have new smarts internally to match up multiple classes on either side of the logical operators...

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