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Akkara
Bodhisattva
Joined: 28 Mar 2006
Posts: 6702
Location: &akkara
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 Posted: Sun May 01, 2016 8:36 am Post subject: C++: class with enum & function taking it, best way to c |
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I'm thinking what's the best way to do error-code returns in C++.
I have a error class that wraps an error-code integer and provides a nicer and hopefully clearer and easier to use interface. Something like this: | Code: | class ErrorCode {
public:
enum err_nums {
e_eof = 1,
e_no_header = 2,
e_no_codec = 4,
e_range = 8,
....
};
ErrorCode() : errnum(0) {}
ErrorCode &raise(enum err_nums e) { errnum |= e; }
/* ... other methods omitted from this example... */
private:
unsigned errnum;
}; |
This generally works (except for the fact I abbreviated the example for clarity, so I don't think this particular one will compile as-is).
However I don't like how the calls are done: | Code: | ErrorCode some_work_function(...)
{
ErrorCode err;
if(bad_thing) {
err.raise(ErrorCode::e_no_header); // <== Ugly line
}
...
return err;
} |
The err.raise function only takes a very specific enum as an argument. It would be nice if I didn't have to write "ErrorCode::" all over the place each time I invoke it.
I tried a few alternatives, but they all seem to have their problems:- Declare the enum globally:
Pollutes the namespace for something that's quite specific to this class
- Declare a second class, ErrorNum, have it hold the enum values. Have ErrorCode publicly inherit from it. And other classes with functions that need access to then privately inherits from ErrorNum:
Seems like a hack. Is inheritance meant to be used this way?
- Define a family of functions, one for each error value, something like raise_e_no_header():
Duplicates a lot of code, becomes unwieldy as the number of possible errors goes up (I'm currently at around 30).
There's probably a "good" way to do this, but I don't know the fine points of C++ well enough to know what it is. Please enlighten me.
Thanks!
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Genone
Retired Dev
Joined: 14 Mar 2003
Posts: 9523
Location: beyond the rim
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| Posted: Mon May 02, 2016 9:01 am Post subject: |
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Well, passing the class namespace qualifier is pretty standard practice.
If you really want to avoid it you could define a global enum encapsulated in a special namespace and import the identifiers from that namespace with 'using ...' if the class qualifier really disturbs you that much. |
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