Re: Exceptions vs. undefined behaviour

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 6 May 2008 18:20:37 CST

Message-ID:

<IY0Uj.72550$FR.292702@twister1.libero.it>

Johan Torp ha scritto:

IIRC, the standard library avoids throwing exceptions so that users
which compile without exception support shall be able to use as much
of the standard library as possible. Is this correct, incorrect or are
there other motivations?

That is not entirely correct. There are several situations where the
library is expected/required to throw an exception. In fact there is a
whole hierarchy of exception classes for that purpose. The library
avoids throwing exceptions in all places where "failure" is not
considered an "error" (for example: std::find) and in few other places.
There are also a few places where exceptions are not thrown and
behaviour is left undefined in case of error. This is usually done for
sake of performances (for example: std::vector<>::operator[]) or to
avoid over-constraining the implementation (std::tr1::shared_from_this).

Will this also be the case for the newly accepted libraries and for
TR2?

It's likely that the same approach described above will be followed for TR2.

Will this "undefined behaviour"-strategy only apply to broken pre-
conditions or will error codes and the like be used for reporting
internal errors?

There is no "undefined behaviour"-strategy. The standard clearly states
when the behaviour is defined and when it isn't. If the behaviour is
defined the standard clearly states if an exception shall be thrown or
if an error condition is reported in some other way. If the behaviour is
undefined, which is usually the case when a precondition is not
satisfied, anything can happen: the implementation might ignore or
report the problem, an exception might be thrown or the application
might crash or anything else.

HTH,

Ganesh

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