February 2009 - Boost-users

[boost::system] Is the library abstraction general enough?
by Lian Cheng 24 Feb '09

24 Feb '09

Hi, all I'm currently building an asynchronous MySQL client API based on Boost.Asio, whose error handling is based on Boost.System. And thus, I wrote some code to wrap MySQL error codes and error messages with Boost.System. While writing the code, I found that the library doesn't provide a general enough abstraction. As the document says, there should always be only one instance of each error_category class. And each error_code instance communicates with its error_category through only the error number. Then here is the problem. MySQL error code is a property of a single MySQL connection. The mysql_errno() and mysql_error() functions both require a MYSQL* connection handle as parameter to retrieve the last error number and error message of the given MySQL connection. And the error messages provided by MySQL API are actually printf format strings. The mysql_error() function fills the format strings with information related to the MYSQL* handle. But in Boost.System, I've got no idea how to pass the connection handle to the error_category::message() function so that a proper error message can be retrieved. Is there any way to fix this problem? Or the library itself is just not general enough? You see, not all error numbers can be directly mapped to a well defined error message string. Cheers Cheng

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[signals2] VS 2005 error with deconstruct.hpp
by Nat Goodspeed 24 Feb '09

24 Feb '09

One small glitch in the 2009-02-11 signals2 snapshot [1]. When a source file containing only: #include <boost/signals2.hpp> is compiled with Visual Studio 2005, it produces: cl /EHsc /I libraries/include signals2-glitch.cpp Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.762 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. signals2-glitch.cpp libraries/include\boost/signals2/deconstruct.hpp(510) : error C2874: using-declaration causes a multiple declaration of 'boost::signals2::detail::deconstruct_access' libraries/include\boost/signals2/deconstruct.hpp(233) : see declaration of 'boost::signals2::detail::deconstruct_access' This is the line in question, near the bottom of boost/signals2/deconstruct.hpp: using detail::deconstruct_access; I'm not sure what the intent is for that line, but removing it solves that problem without, as far as I'm aware, introducing new problems. I've attached a patch file. This line caused me no problems on Mac or Linux. Neither does its removal. [1] http://www.boostpro.com/vault/index.php?action=downloadfile&filename=signal… *** boost/signals2/deconstruct.hpp~ Thu Feb 5 18:58:10 2009 --- boost/signals2/deconstruct.hpp Mon Feb 23 15:05:44 2009 *************** *** 507,514 **** return detail::deconstruct_access::deconstruct<T>(a1,a2,a3,a4,a5,a6,a7,a8,a9); } - using detail::deconstruct_access; - #endif } // namespace signals2 --- 507,512 ----

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Re: [Boost-users] boost::exception - leaking error_info
by Bruce Laing 24 Feb '09

24 Feb '09

> Re: [Boost-users] boost::exception - leaking error_info > Date: Mon, 23 Feb 2009 11:01:08 -0800 > From: Emil Dotchevski <emildotchevski(a)gmail.com> > Subject: Re: [Boost-users] boost::exception - leaking error_info > On Mon, Feb 23, 2009 at 9:31 AM, Bruce Laing > <bruce.laing(a)eng-software.com> wrote: > > Emil, > > > > The platform is vc++ 8, boost 1.37. > > > > Please do keep us posted, it's kind of important for exception objects > not to leak memory. :) Emil, Quick update: my problem seems to have been due to conflicting instances of the runtime library coming into the link. I haven't determined which component is bringing in the dynamic CRT, but in any case, changing /MTd to /MDd fixes the leak, indicating a problem in my project setup and compiler/linker switches, rather than a problem with either boost::exception or the way my code was using the library. - Bruce

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[ASIO] io_service.run() call is not blocking until async_write completes
by nick aschberger 23 Feb '09

23 Feb '09

Hi Folks, I am using boost 1.36, and I have a C++ class that wraps calls to boost::asio sockets. There are two important functions: WriteData -- takes a vector of uint8_t's and uses async_write. WaitForPreviousWritestoComplete -- Here the user expects to block until all their previous writes are complete. Effectively this just calls io_service.run(). A user of this class can will WriteData a few times, and then do some other processing for a bit while the async_write is happening in the background, and then they should block at io_service.run() until the writes complete (and error status etc is checked). It was my understanding that io_service.run() call would block the thread of execution at that point until the pending writes on my output socket were complete. Am I wrong in my interpretation, because I see the user effectively doing: async_write async_write async_write io_service.run() async_write async_write io_service.run() The first call to io_service.run() correctly calls my message handler 3 times, for the 3 writes. The second call to io_service.run() I expect to see the handler called twice, but it is not called at all! If I get a bit tricky and do something like: async_write async_write async_write while (!all_writes_comple_flag){ io_service.run() } (the handler will set all_writes_comple_flag when all writes are complete :) ) then the code is effectively busy waiting at that point until it is done, but I do see the handler entered when I expect. Is there some timing issue occurring here? Perhaps the thread that is managing the socket stuff not had a chance to register that it has a pending write waiting? Am I misinterpreting what boost means in the documentation by saying the io_service.run() function blocks? If I am, what should I do to wait until all asynchronous writes are complete? thanks Nick

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Boost.multi_index: how to use a member function instead ofoperator<()?
by Joost Kraaijeveld 23 Feb '09

23 Feb '09

Hi, I want to use in index based on a member function that returns a bool if an element is smaller than an other element like operator<. But I cannot find how to do that. e.g. using namespace ::boost; using namespace ::boost::multi_index; class Object{ bool operator<(const Object& rhs) const; bool fn(const Object& rhs) const; } struct FnIndex{}; typedef multi_index_container< Object, indexed_by < ordered_unique< identity< Square > >, // this uses operator<(const Object&) I believe? ordered_unique< tag< FnIndex >, ?????????????? > > > ObjectContainer; If this possible, what should I use in the place of ????????? TIA -- Groeten, Joost Kraaijeveld Askesis B.V. Molukkenstraat 14 6524NB Nijmegen tel: 024-3888063 / 06-51855277 fax: 024-3608416 web: www.askesis.nl

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proto user guide e.g.
by Hicham Mouline 23 Feb '09

23 Feb '09

Hi, continuing to work through the user guide boost_1_38_0/doc/html/proto/users_guide.html, I reached the section Retaining POD-ness with BOOST_PROTO_EXTENDS() I fail to compile the following code with intel10: --------------------------CODE----------------------------- #include <iostream> #include <vector> #include <cmath> #include <boost/proto/core.hpp> #include <boost/proto/tags.hpp> #include <boost/proto/context.hpp> #include <boost/proto/domain.hpp> #include <boost/mpl/assert.hpp> using namespace boost; // Define a placeholder type template<int I> struct placeholder {}; // A type to be used as a domain tag (to be defined below) struct calculator_domain; struct calculator_context : proto::callable_context< calculator_context const > { // Values to replace the placeholders std::vector<double> args; // Define the result type of the calculator. // (This makes the calculator_context "callable".) typedef double result_type; // Handle the placeholders: template<int I> double operator()(proto::tag::terminal, placeholder<I>) const { return this->args[I]; } }; // The calculator<> expression wrapper makes expressions // function objects. template< typename Expr> struct calculator { // Use BOOST_PROTO_BASIC_EXTENDS() instead of proto::extends<> to // make this type a Proto expression extension: BOOST_PROTO_BASIC_EXTENDS(Expr, calculator<Expr>, calculator_domain) // Define operator[] to build expression templates: BOOST_PROTO_EXTENDS_SUBSCRIPT() // Define operator= to build expression templates: BOOST_PROTO_EXTENDS_ASSIGN() typedef double result_type; // Hide base_type::operator() by defining our own which // evaluates the calculator expression with a calculator context. result_type operator()( double d1 = 0.0, double d2 = 0.0 ) const { // As defined in the Hello Calculator section. calculator_context ctx; // ctx.args is a vector<double> that holds the values // with which we replace the placeholders (e.g., _1 and _2) // in the expression. ctx.args.push_back( d1 ); // _1 gets the value of d1 ctx.args.push_back( d2 ); // _2 gets the value of d2 return proto::eval(*this, ctx ); // evaluate the expression } }; // Define a calculator domain. Expression within // the calculator domain will be wrapped in the // calculator<> expression wrapper. struct calculator_domain : proto::domain< proto::generator<calculator> > {}; int main() { calculator< proto::terminal< placeholder<0> >::type > const _1 = {{{}}}; calculator< proto::terminal< placeholder<1> >::type > const _2 = {{{}}}; std::cout << ((_1 + _2)(45., 56.)) << std::endl; } -------------------------------- END CODE -------------------------------- The error is: 1>using typeof emulation 1>C:\Program Files (x86)\boost_1_38_0\boost/proto/generate.hpp(153): error: no suitable user-defined conversion from "const boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>> &, const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>> &>, 2L>" to 1> "calculator<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>> &, const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>> &>, 2L>>" exists 1> return Extends<Expr>(expr); 1> ^ 1> detected during: 1> instantiation of "Extends<Expr> boost::proto::generatorns_::generator<Extends>::operator()(const Expr &) const [with Extends=calculator, Expr=boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>> &, const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>> &>, 2L>]" at 1> line 145 of "C:\Program Files (x86)\boost_1_38_0\boost/proto/operators.hpp" 1> instantiation of "Left::proto_domain::result<void (boost::proto::exprns_::expr<Tag, boost::proto::argsns_::list2<Left &, Right &>, boost::proto::argsns_::list2<Left &, Right &>::arity>)>::type boost::proto::detail::as_expr_if<Tag, Left, Right, Left::proto_is_expr_, Right::proto_is_expr_>::make(Left &, Right &) [with Tag=boost::proto::tag::plus, Left=const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>>, 1> Right=const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>>]" at line 290 of "C:\Program Files (x86)\boost_1_38_0\boost/proto/operators.hpp" 1> instantiation of "const boost::proto::detail::as_expr_if<boost::proto::tag::plus, const Left, const Right, void, void>::type boost::proto::exprns_::operator+(const Left &, const Right &) [with Left=calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>>, Right=calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>>]" at line 120 of ".\Test4.cpp" 1> 1>compilation aborted for .\Test4.cpp (code 2)

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Re: [Boost-users] proto user guide e.g.
by Hicham Mouline 23 Feb '09

23 Feb '09

I was using the wrong generator for the domain, it was explained later in the user guide. Apologies,

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[Serialization] Error in serialization of a hash map
by Jack Mullen 23 Feb '09

23 Feb '09

Hi, I'm having a bit of trouble while using the serialization library. (Boost v1.35, gcc, Red Hat Linux). I have a class containing a hash_map (key=string, value=shared_ptr to a class containing a deque): HashMapClass{ friend class boost::serialization::access; template <class Archive> void serialize(Archive &ar, const unsigned in t version){ ar & map; } __gun_cxx::hash_map<std::string const, boost::shared_ptr<DequeClass> map; } //create instance HashMapClass hashMap; // fill hashmap ... //perform serialization every hour or something std::ofstream ofs("file.txt"); boost::archive::binary_oarchive oa(ofs); const HashMapClass &map = hashMap; oa << map; The Problem: This works fine for several saves. I can see the file created changing each time the serialization is done. Then after about four or five saves, it seg faults at the place described below. It looks to me like it's having problems iterating over the hash_map. Any advice on how to diagnose or fix this would be appreciated, Many thanks Jack Segfault at: (__gnu_cxx::_Hashtable_const_iterator<std::pair<std::string const, boost::shared_ptr<HashMapClass> >, std::string const, __gnu_cxx::hash<std::string const>, std::_Select1st<std::pair<std string const, boost::shared_ptr<HashMapClass> > >, std::equal_to<std::string const>, std::allocator<boost::shared_ptr<HashMapClass> > >::operator++()+0xe)[0x65a825a] (boost::archive::detail::oserializer<boost::archive::binary_oarchive, __gnu_cxx::hash_map<std::string const, boost::shared_ptr<HashMapClass>, __gnu_cxx::hash<std::string const>, std::equal_to<std::string const>, std::allocator<boost::shared_ptr<HashMapClass> > >::save_object_data(boost::archive::detail::basic_oarchive&, void const*) const+0x1b2)[0x65a90da] (/usr/lib/libboost_serialization-gcc34-mt-1_35.so.1.35.0(boost::archive::detail::basic_oarchive_impl::save_object(boost::archive::detail::basic_oarchive&, void const*, boost::archive::detail::basic_oserializer const&)+0xd1)[0x8497cd] (/usr/lib/libboost_serialization-gcc34-mt-1_35.so.1.35.0(boost::archive::detail::basic_oarchive::save_object(void const*, boost::archive::detail::basic_oserializer const&)+0x23)[0x849213] (boost::archive::detail::oserializer<boost::archive::binary_oarchive, HashMapClass>::save_object_data(boost::archive::detail::basic_oarchive&, void const*) const+0x15c)[0x65a7db4] (/usr/lib/libboost_serialization-gcc34-mt-1_35.so.1.35.0(boost::archive::detail::basic_oarchive_impl::save_object(boost::archive::detail::basic_oarchive&, void const*, boost::archive::detail::basic_oserializer const&)+0xd1)[0x8497cd] (/usr/lib/libboost_serialization-gcc34-mt-1_35.so.1.35.0(boost::archive::detail::basic_oarchive::save_object(void const*, boost::archive::detail::basic_oserializer const&)+0x23)[0x849213]

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Re: [Boost-users] boost::exception - leaking error_info
by Bruce Laing 23 Feb '09

23 Feb '09

> > > Date: Fri, 20 Feb 2009 19:17:55 -0800 > From: Emil Dotchevski <emildotchevski(a)gmail.com> > Subject: Re: [Boost-users] boost::exception - leaking error_info > On Fri, Feb 20, 2009 at 3:00 PM, Bruce Laing > <bruce.laing(a)eng-software.com> wrote: > > This program seems to be leaking boost::exception::error_info objects. > > Is there something missing here? > > > > - Bruce > > > > What platform? Do you have a complete program that shows the problem? > > This test seems to work as expected: > > #include "boost/exception.hpp" > > class > counter > .... > int > main() > { > c=0; > try > { > throw_func(); > } > catch( an_exception & ) > { > assert(c>0); > } > assert(!c); > } > > Emil Dotchevski > Reverge Studios, Inc. > http://www.revergestudios.com/reblog/index.php?n=ReCode > Emil, The platform is vc++ 8, boost 1.37. Since submitting my inquiry to the list, I cut my boost.exception code out into a separate test program that is very similar to the test code you gave in your reply (thanks for that) , but my test program does not leak, so the problem seems to involve some aspect of context from the original surrounding code that I'm not yet able to identify. I'll write back with an update if I can isolate the interaction that triggers the leakage. - Bruce

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How to use noncopyable?
by Yang Zhang 23 Feb '09

23 Feb '09

Hi, I can't figure out how to properly use noncopyable. I'm always getting things like "has a non-virtual destructor" warnings. In fact, compiling noncopyable_test.cpp gives me: $ g++ -Wall -g3 -o noncopyable_test noncopyable_test.cpp -Wextra -Wconversion -Wpointer-arith -Wcast-qual -Wcast-align -Wwrite-strings -Winit-self -Wno-unused-parameter -Wparentheses -Wmissing-format-attribute -Wfloat-equal -Winline -Woverloaded-virtual -Wsign-promo -Wc++0x-compat -Wsynth /opt/armed/include/boost/noncopyable.hpp: In copy constructor ‘<unnamed>::DontTreadOnMe::DontTreadOnMe(const<unnamed>::DontTreadOnMe&)’: /opt/armed/include/boost/noncopyable.hpp:27: error: ‘boost::noncopyable_::noncopyable::noncopyable(const boost::noncopyable_::noncopyable&)’ is private noncopyable_test.cpp:22: error: within this context noncopyable_test.cpp: In function ‘int main()’: noncopyable_test.cpp:32: note: synthesized method ‘<unnamed>::DontTreadOnMe::DontTreadOnMe(const<unnamed>::DontTreadOnMe&)’ first required here /opt/armed/include/boost/noncopyable.hpp: In member function ‘<unnamed>::DontTreadOnMe&<unnamed>::DontTreadOnMe::operator=(const<unnamed>::DontTreadOnMe&)’: /opt/armed/include/boost/noncopyable.hpp:28: error: ‘const boost::noncopyable_::noncopyable& boost::noncopyable_::noncopyable::operator=(const boost::noncopyable_::noncopyable&)’ is private noncopyable_test.cpp:22: error: within this context noncopyable_test.cpp: In function ‘int main()’: noncopyable_test.cpp:33: note: synthesized method ‘<unnamed>::DontTreadOnMe&<unnamed>::DontTreadOnMe::operator=(const<unnamed>::DontTreadOnMe&)’ first required here Any hints? Thanks in advance. -- Yang Zhang http://www.mit.edu/~y_z/

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