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

[bind] and streaming operators for built in types.
by Robert Jones 26 Aug '09

26 Aug '09

Hi All I've asked a similar question before, but I can't seem to locate the mail or recall the answer! In the code below, how can I eliminate f()? #include "boost/iterator/counting_iterator.hpp" #include "boost/bind.hpp" #include <iostream> using namespace std; using namespace boost; ostream & f( ostream & s, int i ) { return s << i; } int main( ) { for_each( make_counting_iterator( 0 ), make_counting_iterator( 10 ), bind( & f, ref( cout ), _1 ) ); } If I write something like bind( static_cast< ostream & ( * )( ostream &, int ) >( operator << ), ref( cout ), _1 ) the compiler can't locate operator<<() Any thoughts, solutions even? Thanks, - Rob.

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[asio] io_service::run() asserting: "vector iterator not dereferencable"
by Robert Dailey 26 Aug '09

26 Aug '09

Inside of win_iocp_handle_service.write_operation.do_completion_impl(), there is this block of code (Note I'm using Boost 1.40 Beta): #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING) // Check whether buffers are still valid. typename ConstBufferSequence::const_iterator iter = handler_op->buffers_.begin(); typename ConstBufferSequence::const_iterator end = handler_op->buffers_.end(); while (iter != end) { boost::asio::const_buffer buffer(*iter); boost::asio::buffer_cast<const char*>(buffer); ++iter; } #endif // defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING) The call to buffers_.begin() is causing the assert. Looks like a container is getting invalidated/corrupted somehow. I have no idea why this is happening. I'm calling io_service::run() from its own worker thread in a continuous loop like so: for(;;) { boost::this_thread::sleep( boost::posix_time::milliseconds( 20 ) ); m_service.run(); } The class that is wrapping the io_service and serial_port objects invokes a post at construction (from the main thread), to start off a transparent yet continuous chain of reads over the serial port: m_service.post( boost::bind( &SerialClient::DoRead, this ) ); After that, externally I call a function that posts a write in a similar way. This write occurs after the above post for the read: m_service.post( boost::bind( &SerialClient::DoWrite, this, data ) ); When I step through the sequence of events, I see the following happen: - io_service and serial_port are constructed and initialized - io_service thread is started (But run() has not been called yet) - The DoRead() is posted to the io_service - The DoWrite() is posted to the io_service - io_service.run() is called from the worker thread for the first time - DoRead() is called from io_service::run(), which in turn calls serial_port::async_read_some() - DoWrite() is called from io_service::run(), which in turn calls boost::asio::async_write() on the serial_port - ReadCompleted() is invoked as the callback from the previous serial_port::async_read_some() call. It does NOT call async_read_some again (for testing, I disabled the looped reading). - After ReadCompleted() scope exits, it throws the assert Not sure what I'm doing wrong. Keep in mind that this whole time the COM port is not connected to anything, but I'm not sure if this will have anything to do with it. I've attached the code just in case you don't mind looking over it. --------- Robert Dailey

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Question with the date_time libraries: microsec_clock::local_time()
by Kit Li 26 Aug '09

26 Aug '09

Hi, I'm new to Boost and am trying to utilize the date_time libraries. I'm trying use the library in XP. Here's the code I'm testing: ptime now = microsec_clock::local_time(); tz_database tz_db; tz_db.load_from_file("c:/boost/libs/date_time/data/date_time_zonespec.csv"); time_zone_ptr nyc = tz_db.time_zone_from_region("America/New_York"); local_date_time ldt(now.date(),now.time_of_day(), nyc, true); stringstream ss; local_time_facet* output_facet = new local_time_facet(); ss.imbue(locale(locale::classic(), output_facet)); output_facet->format("%Y%m%d, %H:%M:%S %F %z"); ss.str(""); ss << ldt; cout << ss.str() << endl; The question i have is with "microsec_clock::local_time();". I tested second_clock::local_time() and the time is correct, for example 20090826, 15:14:55 EDT. However, when I use microsec_clock::local_time();, I'd get 19700506, 19:44:32.970074 EDT. Is there a conversion somewhere that I'm missing? Thanks for the help. - Bill

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Shared mutex vs normal mutex
by Alessandro Bellina 26 Aug '09

26 Aug '09

Hello I am testing the boost mutex/lock classes in order to implement a multiple reader single writer model. Because of this I thought that the shared mutex with lock_shared and lock_unique would be perfect. I'm finding that the performance is no better than with a simple mutex. My writer is adding a bunch of elements, locking the shared container exclusivelly until it is done. The readers looks at all elements of the container, locking on a per element basis. Any ideas as to why the shared mutex would be slower in this case than the simple mutex? This is the code for my producer thread and my consumers (as a side note, employee_set is a multi index): typedef boost::shared_mutex mutex_type; typedef boost::shared_lock<mutex_type> read_lock_type; typedef boost::unique_lock<mutex_type> write_lock_type; static mutex_type rw_mutex; struct ConsumerThread{ ConsumerThread (employee_set* e):es(e){} void operator()(){ for (int i=0; i<es->size(); i++){ read_lock_type l(rw_mutex); es->get<1>(); } } employee_set* es; }; struct ProducerThread{ ProducerThread(int n, employee_set* e):N(n),es(e){} void operator()(){ write_lock_type l(rw_mutex); for (int i=0; i<N; i++){ es->insert (employee(i, "TestEmployee",100-i)); } l.unlock(); } int N; employee_set* es; };

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makefile
by Shaolin 26 Aug '09

26 Aug '09

Hi Guys How do I include boost dependencies in my makefile ? /usr/local/boost_1_39_0/boost/stage/lib/libboost_program_options-gcc43-mt-1_39.a /usr/local/boost_1_39_0/boost/stage/lib/libboost_thread-gcc43-mt-1_39.a -lpthread

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[asio] poor read performance with 10Mb
by Perry, Daniel 26 Aug '09

26 Aug '09

Hello, I've tried searching the archives without much luck, so here goes... I'm using version 1.37 of the boost libraries and I've implemented a SCGI, http://python.ca/scgi/protocol.txt <http://python.ca/scgi/protocol.txt> , server using the HTTP Server 3 as a starting point. Everything works fine for small requests ~1k, but when I try to send ~10 Mb through the performance is awful. It takes ~90 seconds to transfer the data locally on my pc from one app to another. I've tried profiling the code assuming that I was wasting time somewhere in my code, but the profiler should that the threads that were processing the requests where blocked most of the time and not doing anything. The buffer size that I use to read with is 128kb. I not sure what other information is helpful to diagnose what I'm doing wrong. Any help would be appreciated. Regards, Daniel Perry

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shared_array const member function
by Daya S. Prasad 26 Aug '09

26 Aug '09

Can any body please tell me why operator[] is defined in case of shared_array<T> like this way: Type & operator[](std::ptrdiff_t) const; It reports compile time error. Consider the code: class Widget { std::string classId; public: std::string getClassId() const { return classId; } }; int main() { boost::shared_array<Widget> obj(new Widget[10]); std::string id = obj[7].getClassId (); // Error } In my opinion operator function should be defined as follows: const Type & operator[](std::ptrdiff_t) const; Type & operator[](std::ptrdiff_t) ; Please clear my consfusion. Thanks in advance.

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[bind] Will not compile when passing parameter by-value
by Robert Dailey 26 Aug '09

26 Aug '09

Hello, I have a class called ByteSink that has a move constructor and move assignment operator. I pass an object of type ByteSink into bood::bind() by-value and it fails to compile. First, here is my call to boost::bind(): void SerialClient::Write( ByteSink data ) { m_service.post( boost::bind( &SerialClient::DoWrite, this, data ) ); } The error message I'm getting will be located at the very bottom of this message to prevent clutter. Note that I am compiling on MSVC9 under Windows. Below is what my move constructor/assignment function prototypes look like for ByteSink: /// Uses move semantics. ByteSink( ByteSink& other ); /// Uses move semantics. ByteSink& operator= ( ByteSink& other ); And the compiler error I'm getting (It's a bit lengthy) is below. Any idea what is causing this? My best guess is that boost::bind() is using const somewhere, and it cannot find a copy constructor that takes a const ByteSink as a parameter, since I'm not using a typical copy constructor. 1>C:\IT\third_party\boost_1_40_0_beta1\boost/bind/bind.hpp(859) : error C2558: class 'boost::_bi::list2<A1,A2>' : no copy constructor available or copy constructor is declared 'explicit' 1> with 1> [ 1> A1=boost::_bi::value<SerialClient *>, 1> A2=boost::_bi::value<ByteSink> 1> ] 1> C:\IT\third_party\boost_1_40_0_beta1\boost/bind/bind.hpp(859) : while compiling class template member function 'boost::_bi::bind_t<R,F,L>::bind_t(F,const L &)' 1> with 1> [ 1> R=void, 1> F=boost::_mfi::mf1<void,SerialClient,ByteSink>, 1> L=boost::_bi::list2<boost::_bi::value<SerialClient *>,boost::_bi::value<ByteSink>> 1> ] 1> ..\SerialClient.cpp(32) : see reference to class template instantiation 'boost::_bi::bind_t<R,F,L>' being compiled 1> with 1> [ 1> R=void, 1> F=boost::_mfi::mf1<void,SerialClient,ByteSink>, 1> L=boost::_bi::list2<boost::_bi::value<SerialClient *>,boost::_bi::value<ByteSink>> 1> ]

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[asio] serial_port question
by Robert Dailey 26 Aug '09

26 Aug '09

When reading information from a serial_port, it seems like I'm required to poll the port for data. Is it possible to receive asynchronous events when data is available, kind of like how TCP/IP works? --------- Robert Dailey

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regex icase
by Michał Nowotka 26 Aug '09

26 Aug '09

Hello, in the following class: class MyClass : public boost::regex {...} I want to be able to switch between case-sensitive and non-sensitive matching so i defined this method: void MyClass::setIgnoreCase(bool ignoreCase /* = true */) { assign(str(), ignoreCase? (flags() | boost::regex::icase) : (flags() | (~boost::regex::icase))); } but then I get segmentation fault. I know this is caused by bitwise negation (~) but i don't know why. Do you? -- Pozdrawiam Michał Nowotka

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