CODEWITHSUNDEEP
exceptionerror-code
makoshichi
makoshichi

Reputation: 2390

Defining error codes

Is there a "right way" to define error codes? I mean, I've built a library a while ago that throws custom exceptions, but I targeted the custom error messages to a developer's standpoint. Now I'm wrapping up the GUI and when I catch those exceptions, I need more user friendly messages. That's not a problem in itself, but let's say, I have my ReceiverNotAvailableException exception and NoMessageReceivedException. To me, as a developer, they mean completely different things and have different inner messages, but to the end-user they just mean "User not found". I'd like to display something like "User not found (error X)" where X varies depending on which exception is raised - pretty commonplace if you ask me.

My question is: should I go with X=1, 2 and so forth depending on what kind of exception or should I opt for something more complicated for whatever reason? I know it sounds like a dumb question, but I'd really like to know what the "best practice" (I'm not so fond of the term) is in this case.

BTW, of course I'd have a table mapping each code to its corresponding exception, whichever the case is.

Upvotes: 0

Views: 2134

Answers (1)

Vinko Vrsalovic
Vinko Vrsalovic

Reputation: 340221

If your exceptions can't overlap, then going with a HashTable[ExceptionName] = "Error Message" looks like a sane option. If they can you can use something like the following:

The standard way to define message codes that can overlap (this is, occur at the same time) is to use powers of two:

define ERROR_SYSTEM_DOWN  1
define ERROR_DATABASE_UNREACHABLE 2
define ERROR_SPACE_UNAVAILABLE 4
define ERROR_DISK_DIED 8

and so on. Then, in code you can do

if (disk_died() && no_space()) {
    int errorCode = ERROR_DISK_DIED | ERROR_SPACE_UNAVAIABLE; //Binary or
    return errorCode;
}

Finally, on the receiving end you can:

if (errorCode & ERROR_DISK_DIED == ERROR_DISK_DIED) { //Binary and
    //then, at least, disk died. You can check for the rest in the same way
}

Explanation:

ERROR_SYSTEM_DOWN = 0001
ERROR_DATABASE_UNREACHABLE = 0010
ERROR_SPACE_UNAVAILABLE = 0100
ERROR_DISK_DIED = 1000

Then

1000 | 0100 = 1100

and, on the checking code

1100 & 0100 = 0100

Now, if you are using exceptions you can use the same approach, bubbling up the errorCode as long as exception occur. Although this idiom is more common in C.

Upvotes: 4

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