MATLAB Programming Fundamentals - MathWorks

% Check the number of input arguments.

if nargin < 1

me = MException('MATLAB:notEnoughInputs','Not enough input arguments.');

aac = matlab.lang.correction.AppendArgumentsCorrection('"image.png"');

me = me.addCorrection(aac);

throw(me);

end

% Attempt to read file and catch an exception if it arises.

try

fid = fopen(filename,'r');

d_in = fread(fid);

catch ME1

% Get last segment of the error message identifier.

idSegLast = regexp(ME1.identifier, '(?<=:)\w+$', 'match');

% Did the read fail because the file could not be found?

if strcmp(idSegLast,'InvalidFid') && ...

~exist(filename,'file')

% Yes. Try modifying the filename extension.

switch ext

case '.jpg' % Change jpg to jpeg

filename = strrep(filename,'.jpg','.jpeg');

case '.jpeg' % Change jpeg to jpg

filename = strrep(filename,'.jpeg','.jpg');

case '.tif' % Change tif to tiff

filename = strrep(filename,'.tif','.tiff');

case '.tiff' % Change tiff to tif

filename = strrep(filename,'.tiff','.tif');

otherwise

fprintf('File %s not found\n',filename);

rethrow(ME1);

end

% Try again, with modified filenames.

try

fid = fopen(filename,'r');

d_in = fread(fid);

catch ME2

fprintf('Unable to access file %s\n',filename);

ME2 = addCause(ME2, ME1);

rethrow(ME2)

end

end

end

This example illustrates some of the actions that you can take in response to an

exception.

• Compare the identifier field of the MException object to possible causes of the
  error. In this case, the function checks whether the identifier ends in 'InvalidFid',
  indicating a file could not be found.


• Use a nested try/catch statement to retry the operation with improved input. In this
  case, the function retries the open and read operations using a known variation of the
  filename extension.

26 Error Handling