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How to: get low level file descriptor for tcp::iostream
by Prince Singh 26 May '10

26 May '10

How to: get the low level file descriptor for a tcp::iostream ? -- Regards, Prince Singh Drishti-Soft Solutions Pvt Ltd 62-A, First Floor, Maruti Industrial Area, Sector - 18, Gurgaon - 122016 Haryana, India. W: http://www.drishti-soft.com B: http://blog.drishti-soft.com

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[lambda] extract a constant subexpression by introspection
by alfC 26 May '10

26 May '10

Hello, I have a lambda expression that is suppoalways constructed as [some lambda expression] / ( _1 - c); where c is a double constant, for example c = 3.14. What I need is a function that given the expression returns the internal value of c, if that is possible: template<class LambdaExp> double c(LambdaExp expr){ ... return c in expr assuming that expr has the form [...]/(_1 - c) } The function may throw an exception or whatever if the expr is not of the form [...]/(_1 - c) Some additional infomation that maybe useful to simplify the solution: the lambda expression returns a double, _1 is meant to be a placeholder for double. optional feature: Also it would be ideal if the function could also recognize *simple* alternative expressions like [..]/(_1 + k) (and return -k) or [...]/( k + _1) (and return -k). Solutions using other lambda-like libraries are welcomed too. Thank you, Alfredo

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[shared_ptr] Error in Constructor
by David A. Greene 26 May '10

26 May '10

Using boost 1.42, the attached fails to compile with g++: shared_ptr_test.cpp: In instantiation of ‘Wrapper<A>’: /usr/include/boost/smart_ptr/detail/sp_convertible.hpp:48: instantiated from ‘boost::detail::sp_convertible<Wrapper<B>, Wrapper<A> >’ /usr/include/boost/smart_ptr/detail/sp_convertible.hpp:67: instantiated from ‘boost::detail::sp_enable_if_convertible<Wrapper<B>, Wrapper<A> >’ shared_ptr_test.cpp:33: instantiated from here shared_ptr_test.cpp :14: error: invalid use of incomplete type ‘struct A’ shared_ptr_test.cpp:5: error: forward declaration of ‘struct A’ This is surprising to me as the code does not use A anywhere. I found BOOST_SP_NO_SP_CONVERTIBLE in shared_ptr.hpp and indeed turning that on fixes the problem. Unfortunately, it doesn't seem to be documented. What's the rationale for the enable_if'd constructor? Is BOOST_SP_NO_SP_CONVERTIBLE an official part of the library? Apparently it is causing gcc to check all doSomething members of Action against shared_ptr<Wrapper<B> > and those checks are causing instantiations of Wrapper<A>. -Dave

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[c++-sig]Python binding for templated constructor
by Sandeep Gupta 25 May '10

25 May '10

Hi, I have a class with a generic constructor as follows : class X { indexes m_idx; template<class strategy> X(){ build_indexes<strategy>() }; My problem is that I am not able to figure out the syntax to export this constructor. Is the above class not well defined ?. Thanks. Sandeep

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Re: [Boost-users] [accumulators] Is there a reset function yet?
by Tim Odenthal 25 May '10

25 May '10

On Friday 21 May 2010 21:23:53 boost-users-request(a)lists.boost.org wrote: > > By the way, does the accumulator do something to prevent an overflow when > > I add up everything into one variable? > > No. It uses native intrinsics for raw performance. If you want anything > fancy, you can use your own UDT for samples that check for overflow. > Some construction required. :-( If you do build such a thing, I would > consider making it an official part of Accumulators. Well I'm absolutely no specialist in this, but for my averaging problem it would be enough to compare the "sum" and each new element to 0.5*std::numeric_limits<T>::max()-std::numeric_limits<T>::epsilon() and save the current value "somewhere" (a std::vector?) when this limit is reached. Then, at extraction, one would have to calculate the weighted sum of the entries of that vector. Do you think that's a good approach? > > > And does it prevent a loss of precision, > > when at a late stage the variable I sum everything into is very big, but > > the thing I add is very small? > > No. See above. Here (not being an expert in numerics) I have no clue how to tackle this. A certain loss of precision has to be accepted, probably, but how much is still acceptable? > > > Maybe it would be a good idea to mention this in the documentation, as > > well... > > Indeed. Could you file a ticket at http://svn.boost.org so this doesn't > get lost? Yes, did that. (Ticket #4255) > > Thanks, > > -- > Eric Niebler Thanks, Tim -- Dipl.-Phys. Tim Odenthal Division of Mechatronics, Biostatistics and Sensors (MeBioS) Email: Tim.Odenthal(a)biw.kuleuven.be Full details at http://www.kuleuven.be/cv/u0064388e.htm

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gcc-xml and boost
by Bo Jensen 25 May '10

25 May '10

I am trying to extract function information from my project into a xml file with gcc-xml. The xml file is to be used to make wrappers for other languages. But I get the below failures. I just add all the include directives into a gcc options file and run it. Do I need to set some flags for gcc-xml to parse it correctly ? In file included from /root/src/types/basictypes.hpp:50, from /root/src/logging/logging.hpp:46, from /root/src/exceptions/exc.hpp:70, from ../model/model.hpp:29, from ../model/model.cpp:25: /external/boost/boost/filesystem/operations.hpp:510: error: expected identifier before 'class' /external/boost/boost/filesystem/operations.hpp:511: error: ISO C++ forbids declaration of 'fail_if_exists' with no type /external/boost/boost/filesystem/operations.hpp:511: error: ISO C++ forbids declaration of 'overwrite_if_exists' with no type /external/boost/boost/filesystem/operations.hpp:511: error: expected ';' before '}' token /external/boost/boost/filesystem/operations.hpp:511: error: expected `;' before '}' token /external/boost/boost/filesystem/operations.hpp:511: error: multiple types in one declaration /external/boost/boost/filesystem/operations.hpp:511: error: invalid use of non-static data member 'boost::filesystem::copy_option::fail_if_exists' /external/boost/boost/filesystem/operations.hpp:515: error: from this location /external/boost/boost/filesystem/operations.hpp: In function 'typename boost::enable_if<boost::filesystem::is_basic_path<Path>, void>::type boost::filesystem::copy_file(const Path&, const Path&, boost::filesystem::copy_option)': /external/boost/boost/filesystem/operations.hpp:511: error: invalid use of non-static data member 'boost::filesystem::copy_option::fail_if_exists' /external/boost/boost/filesystem/operations.hpp:519: error: from this location /usr/include/c++/4.4/cmath: In function 'typename __gnu_cxx::__enable_if<std::__is_arithmetic<_Tp>::__value, int>::__type std::fpclassify(_Tp) [with _Tp = float]': /external/boost/boost/functional/hash/detail/hash_float.hpp:65: instantiated from 'size_t boost::hash_detail::float_hash_value(T) [with T = float]' /external/boost/boost/functional/hash/hash.hpp:299: instantiated from here /usr/include/c++/4.4/cmath:501: error: '__builtin_fpclassify' was not declared in this scope /usr/include/c++/4.4/cmath: In function 'typename __gnu_cxx::__enable_if<std::__is_arithmetic<_Tp>::__value, int>::__type std::fpclassify(_Tp) [with _Tp = double]': /external/boost/boost/functional/hash/detail/hash_float.hpp:65: instantiated from 'size_t boost::hash_detail::float_hash_value(T) [with T = double]' /external/boost/boost/functional/hash/hash.hpp:304: instantiated from here /usr/include/c++/4.4/cmath:501: error: '__builtin_fpclassify' was not declared in this scope /usr/include/c++/4.4/cmath: In function 'typename __gnu_cxx::__enable_if<std::__is_arithmetic<_Tp>::__value, int>::__type std::fpclassify(_Tp) [with _Tp = long double]': /external/boost/boost/functional/hash/detail/hash_float.hpp:65: instantiated from 'size_t boost::hash_detail::float_hash_value(T) [with T = long double]' /external/boost/boost/functional/hash/hash.hpp:309: instantiated from here /usr/include/c++/4.4/cmath:501: error: '__builtin_fpclassify' was not declared in this scope

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ASIO async IO, will the buffer corrupt?
by Lloyd 25 May '10

25 May '10

Hello, we are trying to write a high performane storage server. For that we are using Aynchronous IO with boost::asio. The data will be received at the storage server with the help of boost::asio::async_read(), and the data will be written to the storage with boost::asio::async_write() in the asyn_read() completion handler. Here we are planning to share the data buffer. The async read will be running in a loop, so if the write is not completed and if the next async_read() attempts to access the buffer, will the buffer be corrupted? If we use seperate buffer for each async_read()+async_write() operation, wouldn't it be inefficient? Thanks, Lloyd ______________________________________ Scanned and protected by Email scanner

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How to make boost gil io_new extension be able to compile in VS2010?
by blp330 25 May '10

25 May '10

Hi, I post a issue on http://code.google.com/p/gil-contributions/issues/list But it seems like no one noticed. I am trying to compile my code in VS2010 but it will report me that: Detail message: Error 103 error C2668: 'boost::bind' : ambiguous call to overloaded function c:\program files\boost\boost_1_42_0\boost\gil\extension\io_new\detail\bit_operations.hpp line: 63 Does any one know how to solve this problem? Thanks. -- View this message in context: http://old.nabble.com/How-to-make-boost-gil-io_new-extension-be-able-to-com… Sent from the Boost - Users mailing list archive at Nabble.com.

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boost::circular buffer- avoid memory allocation
by Lloyd 24 May '10

24 May '10

Hello, We are using circular buffer. The producer generates the data (a 1024byte char buffer) and the consumer reads it from circular buffer. In normal case the producer allocates the memory for each item. we believe this is very inefficient, so that we are going for circular buffer. How can we make the circualr buffer to allocate the memory in advace and make it possible for the producer and consumer to share it. For example if the buffer is of 10 nodes, the totoal memory allocated by circular buffer would be 10*1024, isn't it? How can the producer get the pointer to the next free node available in the circular buffer? (so as to avoid memory allocation by the producer) How can the consumer get pointer to the data to be read next? The sample available in boost::circular buffer describes it with a simple integer based example. I think this kind of problem is not addressed in it. Some hint will be very useful. Thanks, Lloyd ______________________________________ Scanned and protected by Email scanner

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Re: [Boost-users] boost/numeric/ublas/matrix_sparse.hpp does not play well with RICE
by John O. Woods 24 May '10

24 May '10

Indeed, reversing the #include order seems to work. I thought I'd tried it, but it's compiling just fine now. Thanks so much, John > Date: Sat, 22 May 2010 12:18:02 -0400 > From: Nat Goodspeed <nat(a)lindenlab.com> > To: "boost-users(a)lists.boost.org" <boost-users(a)lists.boost.org> > Subject: Re: [Boost-users] boost/numeric/ublas/matrix_sparse.hpp does > not play well with RICE > Message-ID: <55DB80E1-0E3B-456F-9C8D-E5650C62A409(a)lindenlab.com> > Content-Type: text/plain; charset=us-ascii; format=flowed; > delsp=yes > > On May 21, 2010, at 3:49 PM, "John O. Woods" > <john.woods(a)marcottelab.org> wrote: > > > I've included the current code below. It compiles perfectly if I > > comment the first line. > > > > #include <rice/Data_Type.hpp> > > #include <boost/numeric/ublas/matrix_sparse.hpp> > > int main() { return 0; } > > What if you reverse the order of the #includes? > >

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