Identifying the Cause :: Error Handling (Programming)

Programming

Identifying the Cause

Once an error has been caught, you will need to know the source of the error in order to handle it appropriately. The lasterr function returns information that enables you to identify the error that was most recently generated by MATLAB.

To return the most recent error message to the variable errormsg, type

```
errormsg = lasterr;
```

You can also change the text of the last error message with a new message or with an empty string as shown below. You might want to do this if a lower level routine detects an error that you don't want visible to the upper levels.

lasterr('newerrormsg');   % Replace last error with new string
lasterr('');              % Replace last error with empty string

Example Using lasterr

The matrixMultiply function shown earlier in this section could fail for various reasons. If it is called with incompatible matrices, for example, lasterr returns the following string.

lasterr
ans =
   Error using ==> *
   Inner matrix dimensions must agree.

This example uses lasterr to determine the cause of an error in matrixMultiply.

function matrixMultiply(A, B)
try
   A * B
catch
   errmsg = lasterr;
   if(strfind(errmsg, 'Inner matrix dimensions'))
      disp('** Wrong dimensions for matrix multiply')
   else
      if(strfind(errmsg, 'not defined for variables of class'))
         disp('** Both arguments must be double matrices')
      end
   end
end

When calling the function with two matrices not compatible for matrix multiplication, you get the following error message.

A = [1  2  3; 6  7  2; 0  1  5];
B = [9  5  6; 0  4  9];
matrixMultiply(A, B)
** Wrong dimensions for matrix multiply

When calling the function with a cell array argument, you get a message that addresses that error.

C = {9 5 6; 0 4 9};
matrixMultiply(A, C)
** Both arguments must be double matrices

Handling and Recovering from an Error Regenerating an Error