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[phoenix] v3 extension mechanism for template functions
by alfC 20 Apr '11

20 Apr '11

Hi, In Phoenix2 I used to have the following code to add expressions of type pow<N>(... expr...) which where useful for expressions involving Boost.Units. Is it possible to do something similar with Phoenix3. The usage if macros in the tutorial examples obscures how to add template parameters to the phoenix expression. In Phoenix2 it was straight forward, but I can figure out how to do this in Phoenix3. // phoenix2 code: #include <boost/units/pow.hpp> namespace boost{ namespace phoenix{ template<long N> struct pow_eval{ template <typename Env, typename Arg_> struct result{ typedef typename boost::units::power_typeof_helper<typename boost::mpl::at_c<typename Env::args_type, 0>::type, boost::units::static_rational<N> >::type type; }; template <typename RT, typename Env, typename Arg_> static RT eval(Env const& env, Arg_ const& arg_){ return boost::units::pow<N>(arg_.eval(env)); } }; template<long N, typename Arg_> actor<composite<pow_eval<N>, boost::fusion::vector<Arg_ > > > pow(actor<Arg_> const& arg_){ return compose<pow_eval<N> >(arg_); } }} use as pow<3>(arg1)(l)

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Accumulators: what is the difference between features<> and stats<> ?
by Andrew A 20 Apr '11

20 Apr '11

Is there any difference for example, between accumulator_set< double, features< tag::mean > > acc; and accumulator_set< double, stats< tag::mean > > acc; features and stats seems to be synonyms?

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can't take const ref to tribool's indeterminate
by Phil Nash 19 Apr '11

19 Apr '11

Hi all, The following does not compile (GCC 4.2): #include <boost/logic/tribool.hpp> template<typename T> void byRef( const T& v ) { } // ... byRef( boost::indeterminate ); I realise that indeterminate is actually a function. If I write my own, equivalent, function I can substitute it here and it compiles, however. I can't see what is stopping it from working in indeterminate's case - but I suspect it is to do with some of the operator overloading going on. I couldn't pin it down, though. I can take it by value, of course. What am I missing? Before you ask - yes this is boiled down code. In my real situation I have generic code that doesn't even know about tribool, so I can't special-case it. And I'd rather get to the bottom of why it doesn't work for me - even if the end result is "you can't do that". Thanks and regards, [)o IhIL..

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To produce bjam, put Boost Version 1.46.1 in a deep folder (at least 4 levels I guess)
by JIA Pei 19 Apr '11

19 Apr '11

Hi, to whom it may concern: It looks like many Boost users are arguing that "bjam won't be successfully produced". By reading bootstrap.bat, around line 13, you may notice something like "../../../../******", Yes, that means, Boost root directory must be put at least 4 levels (directory depth). This seems to be a bug of current Boost 1.46.1 Rgds JIA -- Email: jp4work(a)gmail.com cell: +1 7783185816 Welcome to Vision Open http://www.visionopen.com

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[network] Release 0.9.0
by Dean Michael Berris 19 Apr '11

19 Apr '11

Good day everyone, apologies for the cross-post. I just wanted to point everyone interested in the development of the cpp-netlib project to the 0.9.0 release announcement over at C++ Soup: http://cplusplus-soup.com/2011/04/18/cpp-netlib-0-9-0-released/ -- more information about what happened in the library between the beta and the official release can be found there. As earlier mentioned, this version is the pre-1.0 snapshot that is being officially submitted to the Boost C++ Library as Boost.Network. I would like to ask the review wizards to please accept this announcement as a request to put Boost.Network/cpp-netlib into the review queue pending a review manager. I would greatly appreciate volunteers who would like to be the review manager(s) for the Boost.Network review. Have a good one and I definitely hope this helps. Cheers from down under! -- Dean Michael Berris http://about.me/deanberris

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[OT] Boost Users/Developers Down Under?
by Dean Michael Berris 19 Apr '11

19 Apr '11

Hey Everyone! Apologies for the cross post and off-topic, but I just moved to Sydney, Australia and I was wondering whether there are any Boost users/developers that are based here who'd like to get together for a geek out session somewhere in the city? I tried to look at the Boost Users Map (http://goo.gl/O1I15) and I only saw one other Boost user in the area -- maybe there are others lurking around who'd be interested in a meet-up here? :) Cheers from down under! :D -- Dean Michael Berris http://about.me/deanberris

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Select outer face for "Chrobak-Payne Straight Line Drawing"
by jakob brandt 19 Apr '11

19 Apr '11

Hello, I'm a boost-newbie and don't know excactly where to post my question - not only because I have some trouble with my English… sorry for that. My Problem is: I have builded some graphs which always can be drawn with an outer face consisting of 3 certain vertices. Now I am trying to find out if it is possible to select the vertices for the outer face in the Chrobak-Payne Straight Line Drawing. Because if I dont, the drawing-algorithm finds other vertices to set the outer face. Could someone tell me if this was possible without a hugh affort and maybe help me with it? (My cpp-skills arent the best :( … to play things down) I would be very thankfull and happy for any advise or help. Best wishes Jakob

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[system] Dynamic error message with context (like MySQL client API)
by Lian Cheng 19 Apr '11

19 Apr '11

Hi, everyone, I'm writing a MySQL client API wrapper with Boost.Asio and Boost.System. And I want to encapsulate all MySQL error codes with boost::system::error_code. But I found out that error messages corresponding to a specified error code value is designed to be unique within Boost.System, which retrieves the error message from the `message()' method of corresponding boost::system::error_category subclass. MySQL provides an API mysql_error, which accepts a connection handle and returns the error message of the last error on this connection. Also, the content of the error message is dynamic. So here is my question: is there any way to provide context related rather than static error messages with Boost.System? Any reply would be appreciated! Cheers Lian

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Creating interprocess::shared_ptr across processes
by GxL 18 Apr '11

18 Apr '11

Hi all, I've been looking into the "boost::interprocess" library to use shared memory the resides in a non-paged physical memory facilitated by RTX (Real-time Windows extension). According to my understanding it's best to use "managed_external_buffer". I have managed to create the shared memory and create and share objects using raw pointers. I would however prefer using smart_ptr that is offered by the boost::interprocess. The problem I'm having is that I can create the shared pointer for any shared object in one process but when I want to create it's counter-part in the other process, it does not share the "share_count" with the original shared_ptr in the first process. For instance I tried to share a list of integers. So I used the interprocess::list as "named" object and once I crated it (following that "interprocess" documentation) I placed that pointer into a interprocess::shared ptr that I created using the helper function "make_managed_shared_ptr". Now in another process I am able to get hold of the raw pointer to that same list by looking up by the name but cant figure out (did lots of searches about this to no avail) how to instantiate an interprocess::shared_ptr such that it would get the same shared_count object. When I use the "make_managed_shared_ptr" and pass in the raw pointer to the shared object it will create one but with a new "shared_count" which is obviously bad. First I thought that the "make_managed_shared_ptr" is able to resolve and find the already existing "shared_count" and link to that but figured it wasn't the case. Then I thought maybe I need to instantiate the shared_ptr as a named object and then retrieve the same object in another process but can't see the "make_managed_shared_ptr" would support such concept. Then I thought maybe the pre-implemented interprocess shareable types (e.g. vector, list, etc.) derive from "enable_shared_from_this" so I could just call the shared_from_this on the retrieved raw pointer to retrieve the shared_ptr that will be guaranteed to share the "shared_count". None of the above yielded the desired results. I didn't find (by googling) anybody talking about the process of creating a shared_ptr (using the helper method of "make_managed_shared_ptr") across the process so I assume that probably is clear and is able to achieve the mentioned results and I must be missing something awfully obvious. Can somebody please advise on how to achieve this? I am loath to just jump and implement my version of "make_managed_shared_ptr" unless I really have to and I'm sure it's designed to work across the processes. Thanks a in advance for help and guidance. Kind regards gxl

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Re: [Boost-users] [filesystem] std::bad_alloc during dll initialization when migrating to filesystem v3
by Richard Ulrich 18 Apr '11

18 Apr '11

I can not reproduce the behavior with a toy project containing 3 dlls that all use boost::filesystem. It might be some incompatibility with another library. But with filesystem v2 it works. So, what should I look for. I searched google extensively for std::bad_alloc during dll initialization, but found no solution so far. Rgds Richard > Date: Wed, 13 Apr 2011 16:51:41 +0200 > From: Richard Ulrich <richi(a)paraeasy.ch> > To: boost-users(a)lists.boost.org > Subject: [Boost-users] [filesystem] std::bad_alloc during dll > initialization when migrating to filesystem v3 > Message-ID: <1302706301.2665.13.camel@one> > Content-Type: text/plain; charset="us-ascii" > > Hi Guys, > > I'm currently migrating our system consisting of multiple dll's and and > executable to filesystem v3. > The first two dll's that use boost::filesystem load ok, but the third > fails with std::bad_alloc in the locale copy constructor called from > default_locale during the construction of dot_path. > > I don't know if it's relevant, but we usually work with char while > filesystem uses wchar_t for BOOST_WINDOWS_API > > Rgds > Richard

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