try and catch help

In a callback function of a GUIDE gui, I have:

path = get(handles.path_text,'String')
try
    data = importdata(path,'')
    if istruct(data)
        x_k = data.data;
    else
        x_k = data;
    end
    x_k_length = length(x_k);
catch err
    error(end+1) = {'Error: Invalid input path.'};
    fail_status = onfail(handles.check_path);
end

The idea here is if the input path is invalid, it will be caught and handeled so the callback function can continue. However, for some reason, when MATLAB executes the IF statement, it goes to the catch block. I don't understand why.

Answer 1

[Leor Greenberger]

OOPS! should be two s's in isstruct.

getReport(err) in the catch block allowed me to solve it.

Answer 2

[Walter Roberson]

Please do not attempt to use error() as a variable name, especially considering the importance of error() to the try/catch mechanism!

I would tend to suspect that you do not want to use the empty string as the column delimiter.

Are you sure that path is non-empty and a regular string (not a cell array)? Should you not be checking with isempty() and ischar() ?

[Leor Greenberger]

oops. I actually was using error(k) here as a cell array of strings. Did not realize there is an error function as well.. will change the name.

Answer 3

[David Young]

A better solution, and better practice in general, is for the code in the catch block to check the identifier of the error. If it can't handle it properly, it should rethrow the error, so it is reported correctly. In your case the catch block could check err.identifier to see that it was really thrown because of an invalid input path.

Also, since you are only expecting to deal with errors that come from importdata, it might be better to only have that statement in the try block:

try
  data = importdata(...);
catch
  ...
end
if isstruct ...

[Leor Greenberger]

I put the isstruct stuff in the try block because if importdata fails, then I did not want to perform the if isstruct statement, as this would not make sense.

[David Young]

Yes, fair enough. I was thinking in terms of the catch block doing some error recovery or else making an early exit from the function.