Re: Odd Exception Behavior

From:
"Alf P. Steinbach" <alfps@start.no>
Newsgroups:
comp.lang.c++
Date:
Fri, 05 Feb 2010 00:52:43 +0100
Message-ID:
<hkfmke$9k0$1@news.eternal-september.org>
* none:

Alf P. Steinbach wrote:

You're absolutely not the first to walk into that, but perhaps one of
the first here to recognize it yourself -- at least, I can't
remember it happen b4.


I get lucky, on occaision. :) Is there any particular reason why str()
doesn't return by reference? Or, at least, why there isn't an
alternative method available to do so?


It would require the stream to hold a string instance.

Thus it would conflict with a main guideline of the design of the C++ language,
that you don't have to pay for what you don't use.

Some other tips for the code:

   * "C"-prefix for a class is a Microsoft-ism, therefore (almost
   automatically)
      ungood.


Guilty as charged. I've been using the "C" prefix since the early days
of Visual Studio.
 

   * The assignment operator implementaiton is a bit dangerous, think
   about
     assigning twice to same exception object.


I should be checking for "&rhs == this"?


That too, if you choose to implement the assignment operator that way.

But with the code as presented you can accumulate text by repeated assignments.

A generally better way is to let the data members copy themselves. Then the
autoamtically generated assignment operator is good enough. I.e. store strings
instead of streams.

   * The copy function seems to jumble up the short and long messages,
   anyway,
     copy will not be perfect copy with the code as-is.


Yes, the idea was that the "thrower" would not need to set both the
short and long messages. If only one is set, the other will just be a
duplicate.
 

   * The 'cast' operator should perhaps best be 'const'.


Ah, good point.

   * Most importantly, the whole "stream whatever into a string" can
   be
     /separated/ as a very very simple class. Then it can be used for
     whatever.
     :-)


That's interesting. So I would basically be creating a "copyable
ostringstream."

Thanks a lot for the feedback.


I forgot to mention, unless this is meant as a "hard exception" class it should
preferably, directly or indirectly, derive from std::exception.

std::runtime_error is a generally good choice as base class for a custom
exception class.

Cheers & hth.,

- Alf

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