Matlab minimum working example of handling exception higher up in call stack?

问题

I've been browsing Matlab's exception handling pages, and having a bit of difficulty finding a complete minimum working example of an exception being handled by a function in the call stack that is above where the exception is generated. Would anyone be able to point to such a page, or confirm that it is lacking?

Thanks.

回答1:

I had in mind something like the following minimum working example, showing the mechanics in handing an error from an invoked function to a caller. TMW agrees that something like this would fill in a gap in their documentation (they assisted in creating this example).

% main.m
%-------
fprintf(1,'----------------\nRunning foo(1,2)\n')
try
   foo(1,2)
catch ME0
   ME0
end

fprintf(1,'\n');

fprintf(1,'----------------\nRunning foo(1,[2 3])\n')
try
   foo(1,[2 3])
catch ME0
   ME0
end

fprintf(1,'----------------\nRunning foo(0,4)\n')
try
   foo(0,4)
catch ME0
   ME0
end


% foo.m
%------
function foo(A,B)
   try
      barDbar(A,B)
   catch ME1
      fprintf(1,'\n');
      fprintf(1,'Running catch block in %s\n',mfilename)
      ME1, drawnow('update') % Doesn't always flush stdout !!
      % No `throw` command, error doesn't propagate to main as ME0
   end
end

% barDbar.m
%----------
function barDbar(A,B)
   try
      foobar(A,B);      
   catch ME2
      fprintf(1,'\n');
      fprintf(1,'Running catch block in %s\n',mfilename)
      ME2, drawnow('update') % Doesn't always flush stdout !!
      throw(ME2) % Required to "escalate" error to caller
   end
end

% foobar.m
%---------
function V = foobar(V1,V2)
   V = cat(1,V1,V2);               

   fprintf(1,'\n');

   % The following only executes if `cat` does *not* encounter
   % an error
   fprintf(1,'%s encountered no error.\n',mfilename)
   if V1 == 0
      fprintf(1,'Creating artificial exception instead.\n')
      ME = MException( 'foobar:ArtificalException' , ...
                       'foobar added artifical exception' );
      ME, drawnow('update') % Doesn't always flush stdout !!
      throw( ME )
   end % if
end

The output:

----------------
Running foo(1,2)

foobar encountered no error.

----------------
Running foo(1,[2 3])

Running catch block in barDbar
ME2 = 
  MException with properties:

    identifier: 'MATLAB:catenate:dimensionMismatch'
       message: 'Dimensions of matrices being concatenated are not consistent.'
         cause: {0x1 cell}
         stack: [4x1 struct]

Running catch block in foo
ME1 = 
  MException with properties:

    identifier: 'MATLAB:catenate:dimensionMismatch'
       message: 'Dimensions of matrices being concatenated are not consistent.'
         cause: {0x1 cell}
         stack: [3x1 struct]
----------------
Running foo(0,4)

foobar encountered no error.
Creating artificial exception instead.
ME = 
  MException with properties:

    identifier: 'foobar:ArtificalException'
       message: 'foobar added artifical exception'
         cause: {}
         stack: [0x1 struct]

Running catch block in barDbar
ME2 = 
  MException with properties:

    identifier: 'foobar:ArtificalException'
       message: 'foobar added artifical exception'
         cause: {}
         stack: [4x1 struct]

Running catch block in foo
ME1 = 
  MException with properties:

    identifier: 'foobar:ArtificalException'
       message: 'foobar added artifical exception'
         cause: {}
         stack: [3x1 struct]

TMW's Capture Information About Exceptions page shows how, at each level (i.e., each try/catch block), one can create a new exception and append exceptions from lower level functions (instead of just propagating those exceptions upward).

One of the things I found from this experiment was that the exception objects don't automatically get cascaded into a chain of exception objects at each level. This has to be done manually.

Another little detail is that, even though MException can manufacture an exception, it differs from an actual error (or an error created with error) in that it still needs to be thrown explicitly. In contrast, throwing is done automatically by real errors and errors created using error.

来源：https://stackoverflow.com/questions/51272681/matlab-minimum-working-example-of-handling-exception-higher-up-in-call-stack