October 2009 - Boost - lists.preview.boost.org

[system][filesystem v3] Question about error_code arguments
by Beman Dawes 07 Nov '09

07 Nov '09

A POSIX sub-group is looking at C++ bindings for POSIX. They are talking about a filesystem library binding at least loosely based on Boost.System, Boost.Filesystem, and C++ TR2. In looking at http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2838.html, "Library Support for Hybrid Error Handling (Rev 2)", they are concerned about specifying hybrid error handling like this: void f(error_code& ec=throws()); They would rather see it specified like this: void f(error_code* ec=0); One particular concern is that as currently worded, the N2838 proposal requires throws() return a null reference, which they see as relying on undefined behavior. I wasn't at the meeting where the LWG asked that a null reference be mandated; my reading of the standard is that it is unclear if returning a null reference is or isn't undefined behavior. Some of the core folks seem to think it is undefined, but compilers accept it. Although the reference form is usual for C++, the use of anything other than the default is limited, and usually in low-level code at that. Although I could personally live with either form, I'm leaning slightly toward the pointer form. Regardless, I'd like to hear Boosters views on the two interfaces above. Which do you prefer? Why? --Beman

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New boost packaging suggestion for windows
by Julian Bangert 06 Nov '09

06 Nov '09

Hello, yesterday I tried to download the boostpro binaries for windows and I had to download over a gigabyte to get all configurations for VS 2008. Sadly the version also was outdated and in general not that great ( e.g. Installer quite bad to handle and you have to register to download ) . So I decided to build from source and package it for a few friends who also needed these binaries. I managed to compress boost_1_40 ( no source except headers, no python AFAIK , but everything else you get with a standard build ) from over 900MB down to 37MB by using 7z. I uploaded it here https://obliviononline.com/pub/boost/boost_1_40_0.7z . Should boost use this form of releasing binaries in the future for windows ? Alternatively, you could endorse this form, like boostpro is endorsed right now and I could host it on google code, etc . An easy to set up ( just unzip this file ) binary distribution would make compiling boost-dependent software much easier. I would be willing to distribute future releases compatible with VS 2005 and 2008 in this form. Yours, Julian Bangert __________ Information from ESET NOD32 Antivirus, version of virus signature database 4551 (20091028) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com

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[1.41.0] Release branch closed for all changes; beta RC tomorrow
by Beman Dawes 05 Nov '09

05 Nov '09

The release branch is closed for all changes. Unless someone objects strenuously, I'll build a release candidate for the beta tomorrow (Tuesday) morning, eastern US time. --Beman

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loglite - A logging library
by JD 04 Nov '09

04 Nov '09

Hello, It's been a while since a discussion about logging hasn't ran on the boost mailing list. I have a small logging library implementing some of the requirements that were previously deemed desirable during the discussion we had here a couple of years ago. Find it here : http://code.google.com/p/loglite/ I've removed all mention to boost in the code, cause I've made some design choice that wouldn't fit with the boost philosophy. Please have a look and let me know what you think could be improved. An example : [example removed because of the now infamous anti-top-posting gmane feature] Regards, JD

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Build boot 1.40.0 on IBM z/OS (EBCDIC)
by norbert.hanke＠bluewin.ch 03 Nov '09

03 Nov '09

Hi folks, I am trying to build boost on the IBM Mainframe on z/OS USS. I successfully modified the jam bootstrap script and have a running bjam binary now. But when trying to build the boost libraries, I get the error below. Does anybody have a hint what to look for? EBCDIC character encoding on my machine might be the reason: digits 0-9 are encoded as character values 240-249, but I have no idea where to start looking. regards, Norbert > ./bjam /home/u250672/boost_1_40_0/tools/build/v2/util/numbers.jam:22: in numbers.check from module numbers error: 03 in 03 1 17 error: is not a number /home/u250672/boost_1_40_0/tools/build/v2/build/version.jam:50: in version-less from module version /home/u250672/boost_1_40_0/tools/build/v2/build/version.jam:102: in version.check-jam-version from module version /home/u250672/boost_1_40_0/tools/build/v2/util/path.jam:172: in join from module path /home/u250672/boost_1_40_0/tools/build/v2/util/path.jam:207: in path.root from module path /home/u250672/boost_1_40_0/tools/build/v2/util/path.jam:247: in path.glob from module path /home/u250672/boost_1_40_0/tools/build/v2/tools/types/register.jam:25: in load from module types/register /home/u250672/boost_1_40_0/tools/build/v2/kernel/modules.jam:283: in import from module modules /home/u250672/boost_1_40_0/tools/build/v2/tools/stage.jam:19: in load from module stage /home/u250672/boost_1_40_0/tools/build/v2/kernel/modules.jam:283: in import from module modules /home/u250672/boost_1_40_0/tools/build/v2/tools/builtin.jam:25: in load from module builtin /home/u250672/boost_1_40_0/tools/build/v2/kernel/modules.jam:283: in import from module modules /home/u250672/boost_1_40_0/tools/build/v2/build-system.jam:11: in load from module build-system /home/u250672/boost_1_40_0/tools/build/v2/kernel/modules.jam:283: in import from module modules /home/u250672/boost_1_40_0/tools/build/v2/kernel/bootstrap.jam:138: in boost-build from module /home/u250672/boost_1_40_0/boost-build.jam:16: in module scope from module

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Temporary objects
by DE 03 Nov '09

03 Nov '09

hi all unfortunately i'm totally out of time now so i only write my proposal and an example forgive me for that the code #include <algorithm> template<typename type> class temporary : public type { temporary() : type() {} temporary(temporary &a) : type() { using std::swap; swap(static_cast<type&>(*this), static_cast<type&>(a)); } template<typename other> temporary(const other &a) : type(a) {} temporary &operator=(temporary &a) { using std::swap; swap(static_cast<type&>(*this), static_cast<type&>(a)); return *this; } template<typename other> temporary &operator=(const other &a) { type::operator=(a); return *this; } }; example1 temporary<huge_type> foo(const huge_type &a) {//returning temporary object temporary<huge_type> ret; //or even 'ret(a)' //doing something... return ret; } //... huge_type result; result = foo(bar); //somewhere in code only one copy operation -- assignment operator return by value copying overhead is eliminated with help of swap() example2 struct my_type { //... my_type(temporary<my_type> &a) { this->swap(a); } //... my_type &operator=(temporary<my_type> &a) { this->swap(a); return *this; } //... }; temporary<my_type> process(const my_type &item) { temporary<my_type> ret; //processing item... return ret; } //... my_type result = process(item); //somewhere in code //or result = process(item); no temporary object handling overhead at all return by value, copy-construct and assign from temporary objects for free! thank you for attention

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Parallel Tree Merge
by Biddiscombe, John A. 03 Nov '09

03 Nov '09

If I have a representation of a tree and I have sub-portions of it spread across a number of processes (but the whole tree represents a well-formed and simple tree structure). Is there a reasonably straightforward way of doing this using BGL or PBGL. I had hoped that it might be as simple as defining some templated tree structure and using the add operator after gathering pieces onto one node. (The tree structure could be represented as XML where the root would exist on all processes, different sub-nodes and leaves and would occur on different processes - a simple xml merge would probably suffice for my needs right now). If examples using boost libraries ((p)BGL/MPI) or other similar combination exist and anyone can point me to resources I'd be most grateful. (I'm not an expert with BGL so will need some do some learning...) Thanks JB -- John Biddiscombe, email:biddisco @ cscs.ch http://www.cscs.ch/ CSCS, Swiss National Supercomputing Centre | Tel: +41 (91) 610.82.07 Via Cantonale, 6928 Manno, Switzerland | Fax: +41 (91) 610.82.82

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#3541 Support <boost/ptr_map.hpp>
by Olaf van der Spek 02 Nov '09

02 Nov '09

Hi, https://svn.boost.org/trac/boost/ticket/3541 Could a forward header file be created such that #include <boost/ptr_map.hpp> works? The extra ptr_container directory is hard to remember..., I always have to look it up. boost/ptr_* looks much more natural. Greetings, Olaf

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The C++ Post-Processor
by Christian Schladetsch 02 Nov '09

02 Nov '09

Hello, This is a general post about C++. Why is it that the pre-processor (PP) is the source of so much disdain, and yet it is the first resource exploited to 'fix' problems with C++? Why has the PP received so little attention over the years, from its early use as M4? This is a message to the powers that be: the PP is a powerful tool. It provides a 'context-cutting' mechanism for creating and extending solutions. It is a true "meta-programming" system built right into C++. No other language I can think of has a PP. This is often viewed as being a good thing, but I wonder more and more as I get older that a good PP is in fact needed to span some otherwise very difficult boundaries. Other languages are "dynamic" inasmuch as they reflect classes and allow for runtime changes to types and instances. I think we all here agree that this ability is counter to building firm, safe and efficient software. But the PP is similar to that, allowing a degree of dynamicy not otherwise available. Specifically, by exposing concepts to the PP we can leverage reflection and synthesis while building on inheritance and conglomeration. I don't have a point as such; I just wanted to raise the idea of developing M4 and the PP past where it is. There is a lot of low-hanging fruit there. This is evidenced by the fact that a lot of other languages are or can be transliterated to C++. Rather than thinking of C++ as the output, we could be thinking of C++ as the input. Perhaps a way forward for C++ is a good PP and a standards-based implementation of C++ in C++ so it can embed itself. I've written a number of languages, and in each I've had to address the issue of pre-processing. The latest attempts have resulted in a system where it parses and executes via AST input to produce an output that is then parsed by the same system to produce an AST that is then walked to eventually produce machine code. I think this model is best, and would be delighted to see some similar movements in the PP/C++. We have Boost.Wave to start with... Why not give it real Expressions? Loops? Scopes? Classes? Templates? memory management? IO? Is there any interest in a Boost.C++ ? Regards, Christian

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[optional] layout
by Domagoj Saric 01 Nov '09

01 Nov '09

why is boost::optional laid out so that the bool comes before the object's placeholder/storage? this takes up to 7 extra bytes of storage with default alignement and, more importantly, it forces pointer offset adjustment/calculation when accessing a boost::optional<> through a pointer (and trying to access the actual contained object)... it also makes life harder for those of us keen to hackery ;) because it makes the address of an optional different from the address of the actual object within the optional... ps. it would be 'cool' if all of the functionality from boost::optional<> not related to the 'is initialized' bool (conditional destruction, etc...) could be extracted into a separate class (usefull for cases where you have to delay/in-place construct an object but are certain that you will construct it by the point where it needs to be used or destroyed...so you do not need the 'conditional' overhead)... -- "That men do not learn very much from the lessons of history is the most important of all the lessons of history." Aldous Huxley

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