C/C++ Users Journal January, 2005

Trip Report: October 2004

This month, an update on the most recent C++ Standards meeting, and the progress on the C++0x Standard language and library

By Herb Sutter

Herb Sutter (http://www.gotw.ca/) chairs the ISO C++ Standards committee and is an architect in Microsoft's Developer Division. His most recent books are Exceptional C++ Style and C++ Coding Standards (Addison-Wesley).

Whew. As I write this, we just finished up with the fall 2004 ISO C++ Standards meeting, held in Redmond, Washington, USA from October 17-22, 2004. The C++ Standards committee continues to meet twice a year; the next meeting will be in Lillehammer, Norway, on April 10-15, 2005. (See my previous trip report [1] for details about the previous meeting, held in spring 2004 in sunny Sydney, Australia.)

This meeting saw some long days. For example, Monday went until 11:00 pm with a presentation by Andrei Alexandrescu on thread/concurrency support for C++, based on a paper by Andrei and highly respected friends, along with two other evening presentations on the topics of hash-based containers and policy-based design for smart pointers and other library features. On Wednesday, we went until after 9:00 pm with a session led by Bjarne Stroustrup to organize meaningful subgroups to parallelize the C++0x evolution work.

It was a strenuous meeting, but the effort was worthwhile because it led to real progress.

Highlights

Here are the highlights of this meeting:

The first set of Standard Library extensions is technically complete. The final technical changes were voted into the Library Extensions technical report (see also the preliminary version going into this meeting [2]), and this batch of extensions to the C++ Standard Library is now technically complete. An updated version will be sent out for the first of two ISO ballots, which should eat up another year, but the technical work is done. This batch of extensions includes support for new smart pointers (shared_ptr), hash-based containers (for example, unordered_set), type traits, random-number generators, regular expressions, tuple types, a generalized function wrapper, and other stuff including a slew of mathematical functions.
C++ evolution. The Evolution Working Group has worked through several pretty-much-ready standalone proposals to clear the immediate docket, and organized itself for hopefully faster parallel progress in three major areas; see below.
C and C++ cooperation and harmonization continue. The Evolution Working Group voted nearly unanimously to adopt the C99 preprocessor extensions, and those too will come up for vote in Norway in the spring to be included in the new Draft Standard C++. Recall that, at the previous meeting (March 2004), C++ had already officially voted to adopt the C99 Library extensions with only minor necessary tweaks, and also voted to officially begin reviewing the remaining C99 language extensions with a view to improving source-level compatibility between C and C++ (while still being free to recraft or just refuse to adopt any features that prove problematic for C++). I know of no progress on that since the last meeting, but the sentiment is there.

Now let's drill down a little. To make this a self-contained article, I'll recap some of the preexisting status as we go, but focus on the current news and updates from this meeting. For more detailed information about some of the things that I've already covered in the past, see [2].

C++ Language Evolution

The Evolution Working Group has a slew of proposals, where a "slew" is a unit much greater than a dozen, and probably greater than a gross. There's no way everything can get attention, and in addition to triage, it's important to recognize that only those proposals that have people who care enough about them to spend time to work on them will move forward.

At this meeting, the Evolution Working Group moved forward on several proposals that are likely to be ready to be voted on to be added to Draft Standard C++ at our next meeting (Norway, April 2005). Here are some of the proposals that seem most likely to come up for vote, but I want to add the caution that some are still somewhat controversial and any of them might fail to reach consensus: C99 long long; fixing right angle brackets (for instance, making vector<vector<int>> legal without having to put that silly space between the two closing angle brackets, >> versus > >); a static_ assert facility for compile-time assertions; nullptr as a spelling for the null pointer value; strongly typed enumerations; extended friend support; and adopting C99's preprocessor extensions.

That still leaves a lot of work that people want to do and that needs doing. To parallelize and speed up the work of the Evolution Working Group, Bjarne Stroustrup has organized the Evolution Working Group into three chunks. Here they are, with the name of the person chairing each subgroup:

Support for library building (Bjarne Stroustrup): This will focus on areas pertinent to building libraries in C++, including better support for generic programming (concepts, for instance).
Modularity and libraries (Pete Becker): This will focus on standardizing support for libraries (including dynamic libraries) and trying to provide a real module system in C++.
Safety, regularity, and performance (me): This will focus on issues including security, threading, and garbage collection.

There's one more evolution-related group, which we want to fall mostly under the Library Working Group because we'd like the extensions to primarily emphasize library extensions, not language extensions:

Support for novices and incidental programmers (TBD; for now it's Matt Austern): In this area we want to heavily concentrate on providing simplification via libraries, so we'd like this to be led by the Library Working Group.

It'll be interesting to see how much progress we can make on these fronts between meetings over the next six months.

Summary

C++ library extensions are in full swing, and C++ language extensions are moving well. Soon, just a few months from now, we'll see the first changes actually voted into Draft Standard C++0x (perhaps we should call this "ISO C++ v2"). This progress can only benefit programmers everywhere, and there's a lot of exciting work ahead in the next couple of years.

References

[1] Sutter, H. "Trip Report: March 2004," C/C++ Users Journal, June 2004.

[2] ISO/IEC JTC1/SC22/WG21/N1687. "(Draft) Technical Report on Standard Library Extensions" (ISO C++committee working document, September 2004). This document is available online at http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1687.pdf.