July 2009 - Boost-users - lists.preview.boost.org

[Proto] Recreating an expression
by christophe henry 01 Jul '09

01 Jul '09

Hi to all proto experts, I have a grammar whose only goal is to build a type: template <class Expr> struct ActionBuilder with an operator() which simply calls: proto::eval(Expr(),my_context); Unfortunately, I have an expression like: boost::proto::exprns_::expr<boost::proto::tag::plus,boost::proto::argsns_::list2<const A&,const B&> > And the compiler is unhappy about finding no appropriate default constructor (I suppose because of the references). deep_copy is probably not usable inside a grammar definition, so is there an easy way of getting rid of the references (if they are really the problem) or do I have to go and get my MPL canon? I am really just interested in having the recreated expression use a new instance of A and B, not the original ones. Thanks, Christophe _________________________________________________________________ Drag n’ drop—Get easy photo sharing with Windows Live™ Photos. http://www.microsoft.com/windows/windowslive/products/photos.aspx

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interprocess::message_queue thread safety
by Moritz 01 Jul '09

01 Jul '09

Hi everybody, I have a question concerning the interprocess::message_queue. Is the send(..) function thread safe? I have one message_queue and only one thread which is reading messages from the queue. But I have 'n' threads that are writing to the queue. Is there any synchronization mechanism needed to avoid unexpected behavior? Thank You Moritz

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[Locks/Mutex] choices between types
by Axel 01 Jul '09

01 Jul '09

Hello This post may not be well suited to this mailing list. I have some questions about the lockable concept provided in boost. There are many "lock" types, and many "mutex" types. My main question is then : when should I chose a given lock type rather a given mutex type ? Given the fact that some of lock types are not thread-safe, if only one thread needs locks, why should I use one of these lock types and why shouldnt I use some mutex type ? Finally, what were the goals of providing so much different ways to lock/unlock resources ? (I may not be aware of all the concepts related to secure resource access) Since the "lock" et "mutex" types provide ways to lock/unlock access to resources, why are not these types defined under the same name ? Are the concepts they implements much more different than I think ? Thanks Axel

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[tuple][hash] Hashing a tuple question
by Chris Hite 01 Jul '09

01 Jul '09

The code using fusion::fold is elegant, but you still have to define a functor before using it. Couldn't boost just define a default hasher for tuple like the default comparison <boost/tuple/tuple_comparison.hpp>? I've got a tuple with 3 ints in it. I can compare them for free. Why can't I just hash them for free? All we'd have to do is define a hash_value function for tuple that calls fold.

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Getting started with boost: Linker error on boost::system::get_system_category
by Alex Black 01 Jul '09

01 Jul '09

I'm just getting started with boost: - I'm using boost::asio - I'm on Vista x64, using Visual Studio 2008 SP1 - I built the x64 libs using bjam --address-mode=64 .... - I've got my code compiling (but not linking) - I got it pointed to the libs, so it finds the datetime, regex lib etc I get these errors: Error 84 error LNK2001: unresolved external symbol "class boost::system::error_category const & __cdecl boost::system::get_system_category(void)" (?get_system_category@system@boost@@YAAEBVerror_category@12@XZ) Error 85 error LNK2001: unresolved external symbol "class boost::system::error_category const & __cdecl boost::system::get_generic_category(void)" (?get_generic_category@system@boost@@YAAEBVerror_category@12@XZ) any tips? thx - Alex

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Problem of compiling boost::thread source code from Sun Studio
by Carfield Yim 01 Jul '09

01 Jul '09

Get the following error: "/home/ops/3rdParty/boost/1.38.0/install/include/boost-1_38/boost/thread/detail/thread.hpp", line 344: Error: boost::thread::thread(boost::thread&) is not accessible from boost::move(boost::detail::thread_move_t<boost::thread>). Do I need to upgrade the boost library for this ? -- View this message in context: http://www.nabble.com/Problem-of-compiling-boost%3A%3Athread-source-code-fr… Sent from the Boost - Users mailing list archive at Nabble.com.

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String, vector type with stack-allocated internal array (and dynamic array fallback)?
by Boris Dušek 01 Jul '09

01 Jul '09

Hello, for performance reasons, I would like not to have to have a std::wstring (1 allocation/1 deallocation of its character array) in one routine and instead have a wchar_t[MAXSIZE]. But I also would like my code to be correct for sizes bigger than MAXSIZE. Is there some type (in boost or elsewhere, preferable for both basic_string and vector) that defaults to stack-allocated array of some size (preferably configurable by a template parameter), and in case of overflow (i.e. push_back or insert when it's full), would allocate a dynamically-allocated array? This is how it works on MSVC with their STL basic_string implementation, just the array size is unconfigurable (16 bytes including null-terminating byte). I would obviously choose the MAXSIZE so that 99.9% of cases are handled by the stack-allocated array. Thanks, Boris

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Solved it - Re: How to set include path to boost root (when using bjam)?
by s seelenluft 01 Jul '09

01 Jul '09

> > sorry for this very basic question. Bjam complains about not finding the > boost libraries. This line > #include <boost/mathtools/minima.hpp> > in the header of my code triggers: > > error: boost/math/tools/minima.hpp: No such file or directory I have added: :<include>/usr/local/include/boost-1_39 as suggest on page 6 of: http://www.boost.org/doc/tools/build/doc/userman.pdf into the 'body' of exe 'options' in the Jamroot file inside my project. I had previously tried to add it just at the end that file. My problem was that I was provided with a working Jamroot file (by somebody who has since left my organisation) and thus I was able to work happily without knowing anything about the syntax in it. I was foraging through the boost documentation how to get started with it and only found that little bone: " you need a directory containing the boost/ subdirectory in your #includepath. " in: http://www.boost.org/doc/libs/1_39_0/more/getting_started/unix-variants.html but no documentation of how to actually add a include path (because that is probably obvious to anybody familiar with bjam). And, I am wondering whether I should rather add that line to my /usr/share/boost-build/user-config.jam file but the syntax probably is slightly different there. Markus

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How to set include path to boost root (when using bjam)?
by s seelenluft 01 Jul '09

01 Jul '09

Hi, sorry for this very basic question. Bjam complains about not finding the boost libraries. This line #include <boost/mathtools/minima.hpp> in the header of my code triggers: > error: boost/math/tools/minima.hpp: No such file or directory I have installed bjam, works fine (I was provided with an appropiate Jamroot file). I also have installed the boost libraries (via sudo bjam install --prefix=/usr/local/ --toolset=darwin), installation looks ok. I have added /usr/local/include/boost-1_39/** to the header search paths in Xcode, seems to work except for that '*snprintf' *error message (for which I already found some references). However, when invoking bjam from the command line, I somehow have to tell it the location of the boost root directory. I have found some references saying it should be set in the project's Jamrules file: http://boost.cppll.jp/HEAD/tools/build/v1/build_system.htm http://mail.python.org/pipermail/cplusplus-sig/2006-September/010917.html http://lists.boost.org/boost-users/2004/09/7734.php I have tried to add either of the following two lines to either to the end of my Jamroot file or to a separate Jamrules file (both in my project directory): path-global BOOST_ROOT : /usr/local/include/boost-1_39 ; project boost : /usr/local/include/boost-1_39 ; Adding it the Jamrules file does nothing. Adding them to the Jamroot file produces two different error messages: 'rule path-global unknown' and 'error: Invalid project attribute' I have also considered adding these to /usr/share/boost-build/user-config.jam. Just for kicks, I also added '/usr/local/include/boost-1_39' to my path. I know I have to set the include path somewhere (bjam cannot know what version I am using and thus cannot know the precise path). But I am not sure where exactly and don't really know what to add exactly. Thanks. Markus

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General: Vector UTF
by Etienne Philip Pretorius 01 Jul '09

01 Jul '09

Hello List, This is a general question regarding UTF-8/UTF-16/UTF-32 design implementation. I would appreciate and comments to this design. Create classes of utf8/utf16/utf32 who has a public base of std::vector<char>. Make all the std::vector<char> methods private (proxy like approach without the pointer) to avoid calling the public base directly from code without down casting (And the signatures should be diffrent anyway, see below). Re-implement common vector functions as public methods for unicode manipulation from the derived classes of utf* using boost::uint32_t as the code point type. Allow passing of down casted utf* classes into functions that will handle std::vector<char> types (boost::asio). This should also allow direct manipulation of the underlying data. Good/Bad/Terrible Idea? These classes should only be for the manipulation of code points and not for the extraction of characters (combining character classes etc). Etienne

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