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Andy
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 Posted: Wed Sep 28, 2005 5:42 pm Post subject: Mapping error codes to error messages |
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I need to make an error handling framework in which application error
codes can be mapped to pre-defined error messages. The framework would
have C++ exception classes for error information propagation. I however
have no clue on how to map the error codes to the messages, and
efficiently access the messages through a simple mapping class or
function. I know this is not exactly standard C++ that we are
discussing, but is anybody aware of any implementation techniques.
Should it necessarily be a static array indexed by error codes or some
rehash of the error codes.
Cheers,
Andy
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Dan McLeran
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| Posted: Wed Sep 28, 2005 10:03 pm Post subject: Re: Mapping error codes to error messages |
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I would use something like std::map<unsigned int, std::string>. The
unsigned int would be the error code and the std::string would be the
message for that error code.
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Jeff Schwab
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| Posted: Thu Sep 29, 2005 2:56 pm Post subject: Re: Mapping error codes to error messages |
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Andy wrote:
| Quote: | I need to make an error handling framework in which application error
codes can be mapped to pre-defined error messages. The framework would
have C++ exception classes for error information propagation. I however
have no clue on how to map the error codes to the messages, and
efficiently access the messages through a simple mapping class or
function. I know this is not exactly standard C++ that we are
discussing, but is anybody aware of any implementation techniques.
Should it necessarily be a static array indexed by error codes or some
rehash of the error codes.
|
I generally store my error messages in an array, and use error codes as
indexes into the array. My error codes are usually enumerations; I
don't know whether enumerations as array indexes are quite kosher, but
they have worked for me.
If your error codes are distributed across a large space of integers,
you might use them as keys to a switch statement, with one case label
for each error code.
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kanze
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| Posted: Thu Sep 29, 2005 8:31 pm Post subject: Re: Mapping error codes to error messages |
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Dan McLeran wrote:
| Quote: | I would use something like std::map<unsigned int,
std::string>. The unsigned int would be the error code and the
std::string would be the message for that error code.
|
Depending on how the error codes and messsages are being
maintained, char const*[] is likely the simplest solution.
(Note that if errors may occur during the construction of static
objects, a solution which uses static initialization is almost a
necessity. So no std::string, no std::vector and no std::map.)
Of course, if the error codes are pre-defined, and very sparce,
this may not work. If order of initialization is not a problem,
std::map is a very good solution. Otherwise, I've found that
something like:
static struct MessageMap
{
unsigned int code ;
char const* message ;
} const map[] =
{
{ Error1, "whatever went wrong" },
// ...
}
works well. Most of the time, a simple linear search
(std::find) is sufficient; if not, it's generally not too hard
to sort the table and use std::lower_bound on it.
--
James Kanze GABI Software
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
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Maciej Sobczak
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| Posted: Thu Sep 29, 2005 8:31 pm Post subject: Re: Mapping error codes to error messages |
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Andy wrote:
| Quote: | I know this is not exactly standard C++ that we are
discussing
|
It *is* a standard stuff, see std::messages class.
The fact is that I've never seen it used in practice - probably because
there are too many things that are left "implementation-defined".
| Quote: | is anybody aware of any implementation techniques.
|
Go for the std::map solution as already suggested, it is easy to
implement and quite extensible as well.
--
Maciej Sobczak : http://www.msobczak.com/
Programming : http://www.msobczak.com/prog/
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adebaene@club-internet.fr
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| Posted: Thu Sep 29, 2005 8:32 pm Post subject: Re: Mapping error codes to error messages |
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Andy wrote:
| Quote: | I need to make an error handling framework in which application error
codes can be mapped to pre-defined error messages. The framework would
have C++ exception classes for error information propagation. I however
have no clue on how to map the error codes to the messages, and
efficiently access the messages through a simple mapping class or
function. I know this is not exactly standard C++ that we are
discussing, but is anybody aware of any implementation techniques.
Should it necessarily be a static array indexed by error codes or some
rehash of the error codes.
|
Do you have any internationalization concern (ie, do the error messages
need to be localized)?
If yes, the map <Error Code> <--> <Error Message> should be in some
kind of external resource (a file, a database, whatever is available on
your environment) and you should havesome kind of framework to retrieve
the correct translation, based on the current locale.
Arnaud
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