September 2008 - Boost-users - lists.preview.boost.org

globals best-practices (avoiding multiple definitions)
by craigp 06 Sep '08

06 Sep '08

Hi - I'm trying to understand the best practice for handling globals (within a namespace), and in particular, avoiding multiple definitions (whether multiple "private" copies or collisions causing a linker error). For namespace globals, if I do something like this (in a header file): namespace log_categories { static log_t server(log_t::category("http.server.server")); } I'd guess that each translation unit (TU) would get its own copy of log_categories::server (or maybe some compilers give a multiple-definition link error, while others would just make multiple private copies?). OTOH, if I only declared the variable and put the definition in a c++ file, there would only be a single copy. For class static members, you cannot initialize the members "in-line" (unless it's an integral constant). One interesting "work-around" I saw in asio/error.hpp was this: namespace boost { ... static const boost::system::error_category& system_category = boost::asio::error::get_system_category(); ... This way, there might be multiple copies but they will all be references to the same underlying object. For the case of class template static members, I found this example in complex.hpp: namespace boost { namespace numeric { namespace detail { template<typename T> struct one_complex { static std::complex<T> const value; }; template<typename T> std::complex<T> const one_complex<T>::value = std::complex<T>(numeric::one<T>::value, numeric::one<T>::value); } ... Is it guaranteed that there will only be one instance of one_complex<T>::value for each T, even if this header file is included in multiple TU's? In this case it doesn't matter (it's a constant), but in other cases I need to ensure that it's a true singleton. Is there a good resource on best-practices for this? I've been bitten by the "multiple-definition" bug in several guises before (eg: in windows when there were multiple libraries linking to the same dll). I googled, and saw suggestions from, say, DEC (http://www.helsinki.fi/atk/unix/dec_manuals/cxx_6.0/cxx570_ug_004.html) which were to put template definitions in separate "template definition files." I take it complex.hpp is best-practice (standards-compatible, portable, etc - at least with certain options set on a particular vendor's compiler, say, automatic template instantiation)? Handling declarations vs definitions of template specializations seems even more fraught, but thankfully I don't have to worry about that for now (plus, it would certainly simplify things to always keep both template decls and defs in the same header file). thanks, --craig

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More bimap issues
by Sean Farrow 06 Sep '08

06 Sep '08

Hi: I have the following code: struct VectorComp { bool operator()(const std::vector<std::bitset<6>>& lhs, const std::vector<std::bitset<6>>& rhs) const { return false; } }; typedef boost::bimaps::bimap<boost::bimaps::set_of<std::vector<std::bitset<6>>, VectorComp>, int> SignsList_Type; SignsList_Type SignsList; When compiling this code, I get c2676 errors from visual studio: 8 error C2676: binary '<' : 'const std::bitset<_Bits>' does not define this operator or a conversion to a type acceptable to the functional 143 I have BitsetComp which successfully compares two std::bitsets. How do I insert this so that my code works succesfully? Cheers Sean. __________ Information from ESET NOD32 Antivirus, version of virus signature database 3421 (20080906) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com

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Re: [Boost-users] [timer] eclapsed return zero
by gmail 06 Sep '08

06 Sep '08

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Re: [Boost-users] [timer] eclapsed return zero
by raindog＠macrohmasheen.com 06 Sep '08

06 Sep '08

Perhaps your thread has been preempted during execution causing the delay. ------Original Message------ From: gmail Sender: boost-users-bounces(a)lists.boost.org To: boost-user-list ReplyTo: boost-users(a)lists.boost.org Sent: Sep 5, 2008 4:15 AM Subject: [Boost-users] [timer] eclapsed return zero Hello, I have used the timer class in my application. It works ok sometime but i think it dont work correctly. my code is: #include <iostream> #include "boost/timer.hpp" using namespace std; using namespace boost; int main() { int count=0; timer t; for(;count<1000000;++count); cout<<t.elapsed(); return 0; } and the output: 0.015 execute time :0.062s sometime the output is: 0 execute time :0.015s regards hechao _______________________________________________ Boost-users mailing list Boost-users(a)lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users Sent from my Verizon Wireless BlackBerry

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[string_algo] implementation functor for classification predicates doesn't implement result_of
by Adam Merz 05 Sep '08

05 Sep '08

The implementation functor for the String Algorithms library's classification predicates ( boost::algorithm::detail::is_classifiedF in boost/algorithm/string/detail/classification.hpp ) doesnt have a result_type typedef or a result struct. Consequently the classification predicates do not work with boost::bind. For a future release of Boost, please add 'typedef bool result_type;' into the struct.

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Warning c4002 with boost_foreach
by Sean Farrow 05 Sep '08

05 Sep '08

Hi: Could somebody please tell me why I get a warning c4002 with the following boost::foreach declaration? BOOST_FOREACH( boost::bimaps::bimap<boost::bimaps::set_of<std::vector<std::bitset<6>>>, int>::left_reference CurrentSign, SignsList.left ) Should I use a typedef instead? Sean. __________ Information from ESET NOD32 Antivirus, version of virus signature database 3420 (20080905) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com

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[Thread]Deadlock using shared_mutex with unique_lock
by Stanislav Stoyanov 05 Sep '08

05 Sep '08

Hi everyone, I am trying to use shared_mutex with unique_lock but my program blocks. I am using boost 1.35. My compiler is MSVC 8.0.50727.762 and my OS is Windows 2000. Here is a minimal code to reproduce the problem: #include "boost/thread.hpp" #include "boost/thread/shared_mutex.hpp" #include "boost/bind.hpp" class Executor { public: void run() { boost::unique_lock<boost::shared_mutex> lock(theMutex); boost::thread::sleep(boost::get_system_time() + boost::posix_time::millisec(30)); } private: boost::shared_mutex theMutex; }; void main() { Executor ex; boost::thread_group group; for(int i=0; i<200; i++) { group.create_thread(boost::bind(&Executor::run, &ex)); } group.join_all(); } The program blocks during the call of group.join_all(). According to the Boost.Thread documentation, unique_lock<boost::shared_mutex> lock(theMutex) acquires exclusive ownership of theMutex. Therefore, I expect that the behaviour of boost::unique_lock<boost::shared_mutex> lock(theMutex); is the same as if a boost::mutex is used. Is my assumption correct or am I missing something? Thank you for any help you can provide, Stanislav

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Linker error for thread methods
by Marc Riese 05 Sep '08

05 Sep '08

Hi, I'm trying to use the boost::thread library in an own dll with Visual Studio 2003. I'm using boost 1.36.0 and built it myself with bjam according to http://www.boost.org/doc/libs/1_36_0/more/getting_started/windows.html First I tested with a simple example, that I've found somewhere in the documentation: struct thread_alarm { thread_alarm(int secs) : m_secs(secs) { } void operator()() { boost::xtime xt; boost::xtime_get(&xt, boost::TIME_UTC); xt.sec += m_secs; // boost::this_thread::sleep(xt); } int m_secs; }; boost::thread thrd(thread_alarm(1)); This code runs and compiles fine. I can add a loop and some couts in the operator() for example and get the output parallel to my application. But when I uncomment the line boost::this_thread::sleep(xt);, I get the following linker error: error LNK2019: unresolved external symbol "bool __stdcall boost::this_thread::interruptible_wait(void *,struct boost::detail::timeout)" (?interruptible_wait@this_thread@boost@@YG_NPAXUtimeout@detail@2@@Z) referenced in function "void __stdcall boost::this_thread::interruptible_wait(class boost::posix_time::ptime const &)" (?interruptible_wait@this_thread@boost@@YGXABVptime@posix_time@2@@Z) The same occurs for other thread methods like yield(). I assume there's a problem with the calling convention, but using something other than __stdcall is not an option for me, since I have to comply with a given specification. I didn't find any information about calling conventions in the boost documentation. Is there a solution for this, or does the boost::thread library require the __cdecl calling convention? Regards, Marc

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comparing objects using boost
by Reena Dass 05 Sep '08

05 Sep '08

Is there something available to compare objects using boost, similar to java.lang.Object Equals? Reena

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newbie: debugging programs with boost
by p＠dirac.org 05 Sep '08

05 Sep '08

Hi all, I'm having trouble using GDB with my program that uses boost. In GDB (bra is a vector<double>): (gdb) print bra(j) Invalid data type for function to be called. I've compiled my program with -g3. How can I peek at boost datatypes? Thanks!

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