TITLE: STL is exception safe

(Newsgroups: comp.lang.c++.moderated,comp.std.c++,comp.lang.c++, 20 Feb 98)

AUSTERN: Matt Austern <austern@isolde.mti.sgi.com>

I wrote an article about exceptions and the standard C++ library
("Making the World Safe for Exceptions") that was published in the
January 1998 issue of C++ Report.  Unfortunately, when I actually read
that issue a couple of weeks ago, I noticed that something very
important had failed to get printed: an author's note that I intended
to go at the end of the article.  Someone---maybe an editor, maybe
me---goofed.

The problem is that I originally wrote that article almost a year ago,
and some of the things I said in it are no longer true.  My intention
was to note, briefly, some of the things that had changed.

First, it is no longer true that the C++ standard says nothing about
exception safety and the standard library.  The standard containers
and algorithms are explicitly guaranteed to be exception safe.  (Using
the terminology of my article, all STL algorithms and containers have
Level 3 exception safety provided that their template arguments
satisfy the appropriate restrictions, some have Level 4 exception
safety, and some are guaranteed not to throw exceptions at all.)

Second, there are now some new techniques for exception safety of
generic conatiners in addition to the ones that I discussed in that
article.  In some cases the new techniques (I'm thinking in particular
of the base class initialization technique) are cleaner and more
efficient than the equivalent ones from my article.

Third and most important, Dave Abrahams is responsible for many of
these changes.  He did a lot of work on exception safety of generic
containers, and he managed to convince the C++ standardization
committee that guarantees of exception safety were important and
practical.

I'm sorry that this note didn't get printed along with my article.