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Re: Error codes vs. exceptions

Cross-posted to 2 groups.

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On 5/28/2012 11:15 PM, mike3 wrote:
> Hi.
>
> I've heard about this, and wonder when is it right to use codes, and
> when to use exceptions for reporting errors? I've heard various stuff,
> such as that exceptions should only be used to indicate "exceptional"
> conditions. Yet what does that mean? I've heard that, e.g. a user
> inputting invalid input should not be considered "exceptional", but
> something like running out of memory should be. Does this mean that if
> we have a program, and we have a "parse()" function that parses a
> string input by the user, that this function should return an error
> code on parse failure, instead of throwing an exception? Yet we'll
> probably also come across places where it's good to use an exception,
> in the same program! Which means we get into _mixing error codes and
> exceptions_. And what's the best way to do that?
>

maybe more like this:
use error codes if it can be reasonably done so;
use exceptions if error codes wont really work.

usually, this means returning an error code if the operation can be 
handled as a no-op and otherwise the program can continue as normal 
(like, "well, that didn't work").

use an exception if this represents a case where normal operation can no 
longer reasonably continue (all action past this point is no longer 
likely to be in a valid state, such as detecting that some internal 
program state is critically wrong).

if it is not clear to use, probably I would opt with error codes.
(usually, when an exception is needed, it is "fairly obvious").


> Also, how exactly does one go about determining what is and is not
> "exceptional"? Two examples were mentioned of things exceptional and
> non-exceptional, but what about something else, like say in a game,
> where you have a grid representing a game level, and a request for a
> tile of the level is made with a coordinate that is off the map (like
> a 64x64 map and something requests a tile at (100, 100).). Would it be
> OK for the function working on the tile to throw? Or should it give an
> "out of range" error code? And as for that mixing: consider, e.g. C++
> and probably many other languages: a function has a single definite
> return type. Suppose our grid had a function that extracts an
> attribute from a cell. What to do when there's an out-of-bounds
> request? Throw exception? See, what I've currently been doing, and
> it's probably silly, is to use exceptions when our function needs to
> return a value, and error codes when it could otherwise return "void".
> This doesn't seem like a good idea. But what to do? Make every
> function return an error code, using pointers to output variables to
> store output, and only use exceptions for a rare few kinds of "system-
> related" error? Yet one can hardly deny the niceness of being able to
> say "x = f() +<foo>" (inside a "try" block, perhaps) instead of
>
> if(f(&x) != SUCCESS)
>   { // handle error }
> x += foo;
>
> :)
>
> Note how we can easily get LONG methods full of repeated code with
> error codes (repeated error handlers to handle similar errors at
> various function calls calling error-code-emitting functions, if one
> wants to be more graceful than simply aborting with an error to the
> next level up (which complicates what error codes a function can
> return, since it can return its own codes in addition to those
> returned by the functions below it, and those may have functions below
> THEM, and so on...).). And who likes duplicated code? eww. This seems
> a disadvantage of error codes.
>
> Or, and this is what I've been thinking of, use exceptions for every
> error that the user does not have control over, like invalid input
> strings. Would that be OK or excessive use of exceptions? And if we
> are to mix error codes and exceptions, does this mean we should have
> the lists of codes and exceptions correspond + a translator to
> translate between the two?


if the function returns a void, use it to return an error code;
if the function returns a pointer, one can potentially return NULL, and 
have another operation to fetch the actual error code (stored off in a 
variable somewhere);
if the function returns a number, then it is a little harder, sometimes 
it can be ">=0 for success, <0 for error", but if the function may 
return the full range, it is a bit harder.

one way I have handled it is to have it be similar to the pointer case, 
where a certain value (0 or -1), "may" represent an error, and whether 
or not it really does is determined by retrieving the error code.

NaN is also a possible error value for floating-point numbers, but is 
rarely used this way.

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Error codes vs. exceptions mike3 <mike4ty4@yahoo.com> - 2012-05-28 21:15 -0700
  Re: Error codes vs. exceptions BGB <cr88192@hotmail.com> - 2012-05-29 00:10 -0500
    Re: Error codes vs. exceptions mike3 <mike4ty4@yahoo.com> - 2012-05-28 22:41 -0700
      Re: Error codes vs. exceptions BGB <cr88192@hotmail.com> - 2012-05-29 01:34 -0500
    Re: Error codes vs. exceptions Adam Skutt <askutt@gmail.com> - 2012-05-29 07:16 -0700
      Re: Error codes vs. exceptions BGB <cr88192@hotmail.com> - 2012-05-29 09:45 -0500
  Re: Error codes vs. exceptions Marcel Müller <news.5.maazl@spamgourmet.com> - 2012-05-29 09:08 +0200
    Re: Error codes vs. exceptions mike3 <mike4ty4@yahoo.com> - 2012-05-31 13:52 -0700
      Re: Error codes vs. exceptions Ian Collins <ian-news@hotmail.com> - 2012-06-01 09:08 +1200
        Re: Error codes vs. exceptions mike3 <mike4ty4@yahoo.com> - 2012-05-31 22:32 -0700
  Re: Error codes vs. exceptions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-05-29 09:37 +0200
  Re: Error codes vs. exceptions "io_x" <a@b.c.invalid> - 2012-05-29 10:00 +0200
  Re: Error codes vs. exceptions Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-05-29 12:24 +0000
  Re: Error codes vs. exceptions Nobody <nobody@nowhere.com> - 2012-05-30 15:23 +0100
    Re: Error codes vs. exceptions BGB <cr88192@hotmail.com> - 2012-05-30 09:40 -0500
      Re: Error codes vs. exceptions Adam Skutt <askutt@gmail.com> - 2012-05-30 08:04 -0700
        Re: Error codes vs. exceptions BGB <cr88192@hotmail.com> - 2012-05-30 12:01 -0500
  Re: Error codes vs. exceptions Jeff Flinn <TriumphSprint2000@hotmail.com> - 2012-05-30 14:18 -0400
    Re: Error codes vs. exceptions Patricia Shanahan <pats@acm.org> - 2012-05-30 13:00 -0700
    Re: Error codes vs. exceptions Adam Skutt <askutt@gmail.com> - 2012-05-30 21:25 -0700
  Re: Error codes vs. exceptions Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2012-05-30 22:44 -0400
    Re: Error codes vs. exceptions Nobody <nobody@nowhere.com> - 2012-05-31 05:04 +0100
    Re: Error codes vs. exceptions Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2012-06-01 21:44 -0400
  Re: Error codes vs. exceptions "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2012-06-02 08:39 +0200
    Re: Error codes vs. exceptions BGB <cr88192@hotmail.com> - 2012-06-02 16:31 -0500
    Re: Error codes vs. exceptions mike3 <mike4ty4@yahoo.com> - 2012-06-02 15:49 -0700
      Re: Error codes vs. exceptions Ian Collins <ian-news@hotmail.com> - 2012-06-03 11:17 +1200
      Re: Error codes vs. exceptions Rui Maciel <rui.maciel@gmail.com> - 2012-06-03 16:38 +0100
    Re: Error codes vs. exceptions Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2012-06-03 20:26 -0400
  Re: Error codes vs. exceptions gremnebulin <peterdjones@yahoo.com> - 2012-06-20 12:05 -0700

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