Re: [Boost-users] [Test] Making use of boost::exception_diagnostic_information and friends

Subject: Re: [Boost-users] [Test] Making use of boost::exception_diagnostic_information and friends
From: Gennadiy Rozental (rogeeff_at_[hidden])
Date: 2009-08-10 17:58:22

Emil Dotchevski wrote:
>>> catch( foo & e )
>>> {
>>>     //do other stuff, and then:
>>>     std::cerr << boost::diagnostic_information(e);
>>> }
>>> catch( boost::exception & e )
>>> {
>>>     //do other stuff, then:
>>>     std::cerr << boost::diagnostic_information(e);
>>> }
>> 1. Isn't supposed to be other way around: first catch boost::exception,
>> followed
>> by catch foo? I'd prefer to have boost:exception related logic in a single
>> catch
>> clause instead of being spread between 20.
> 
> I was implying that you normally catch more specific exceptions first.
> If you don't care about foo in particular you can use a generic catch
> like catch(boost::exception/std::exception) or catch(...).

I do. I hoped I can handle throw foo() in catch( foo ) and 
BOOST_THROW_EXCEPTION( foo() ) in catch( boost::exception ). Former 
would not try to dig inception point info. Later would.

Actually I might want to do it in all clauses after all. I do want to be 
as specific as possible. An alternative is to somehow deduce type at 
runtime in generic catch boost::exception clause, but this seems non 
reliable.

>> 2. I do not want to print anything. I collect information and return it (by
>> throwing another exception) to the higher level, which in turn decides how
>> and
>> where to report it.
> 
> I don't see the point of throwing another exception 

I need to report the error somehow, don't I? Including all the details.

> but if that's what
> you want to do then you could use boost::exception_ptr:
> 
> catch(...)
> {
>   BOOST_THROW_EXCEPTION(another_exception(boost::current_exception()));
> }

I do not see why I need BOOST_THROW_EXCEPTION. I do not care about this 
exception inception point. I know it ;) Also I throw this exception in 
all cases when an error occurred (for example in case if signal 
triggered). It operates on strings and numbers.

> Later on, when you catch(another_exception &), you can pass the stored
> exception_ptr to boost::diagnostic_information, and you'll get
> diagnostic information about the exception it holds (the one captured
> by boost::current_exception() in the original catch(...)). Or you can
> rethrow it and use suitable catches to handle it.

That's fine. As I said I want only inception point and "cause" string 
and I want to format final message myself.

>>> catch( std::exception & e )
>>> {
>>>     //do other stuff furst, then:
>>>     std::cerr << boost::diagnostic_information(e);
>>> }
>>> catch( ... )
>>> {
>>>     std::cerr << boost::current_exception_diagnostic_information();
>>> }
>> What is the point of trying to dig something here? Wouldn't the
>> boost::exception based exception will always be caught in 'catch
>> boost::exception' clause above?
> 
> If all you do is get diagnostic_information, then just the catch(...)
> is sufficient.

But If I already have catch( boost::exception ) I should not try to dig 
this info in catch(...) right?

>>>> 3. I pretty much only need file, line and function name. Are you
>>>> saying I can't do what you are doing inside diagnostic information
>>>> to get a hold of them?
>>> If the exception was thrown by BOOST_THROW_EXCEPTION, then yes you'd
>>> have file, line and function name.
>> Ok. So how do I do this?
> 
> Use get_error_info<throw_function>(e), get_error_info<throw_file>(e),
> get_error_info<throw_line>(e).

What is the requirement on type of e? can it be char*? Or std::string?

>>> However, objects that derive from
>>> boost::exception can have data of arbitrary type, some of it added at
>>> the point of the throw, some of it added later (meaning, it depends on
>>> the callers of the function that throws.)
>>>
>>> Do you not want to display all that information when you catch a user
>>> exception in the testing framework?
>> I do not mind if method 'what' would generate "rich" error message including
>> everything, but the information about the point of inception (Or some other
>> method)
> 
> The problem with what() is that some programmers use it to return a
> user-friendly message. This is incorrect because in general
> user-friendly messages have to be localized which clearly goes beyond
> what()'s interface. 

Can we have something like 'cause', which will be the same as 
diagnostic_info, but without inception point?

Gennadiy