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

[filesystem] Extracting a relative path.
by Robert Jones 13 Jul '09

13 Jul '09

Hi All I'm trying to understand how to determine the relative path of one absolute path to another. So, c:\a\b\c.d relative to c:\a and I'd like the answer to be b\c.d I thought this would be easy to do, but I can't see how. Any thoughts? Thanks, Rob.

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[Tuple] What's the point?
by Robert Jones 13 Jul '09

13 Jul '09

I know that sounds like a slightly flippant question, but I really don't get it. I've used tuples a few times, always for the multiple return value behaviour using tie( ), but in the end it always seems to be a better solution to use a struct. Code like t.get<1>( ) = "fred"; is a bit non-obvious, compared to t.forename = "fred"; So have I entirely missed the point of tuples? Thanks, Rob.

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understanding placeholders
by Ozgur Ozturk 13 Jul '09

13 Jul '09

Hi, I see in the code some functions are passed things like boost::asio::placeholders::bytes_transferred. But I didn't understand what is going on, what are their aim? I found they are defined in placeholders.hpp as boost::arg<2>& bytes_transferred = boost::asio::placeholders::detail::placeholder<2>::get(); //and the get function as template <int Number> struct placeholder { static boost::arg<Number>& get() { static boost::arg<Number> result; return result; } }; TIA, Best regards, Ozgur (Oscar) Ozturk www.DrOzgur.com +1 (614) 805-4370

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Deadline_timer problem
by Mario Chacon 13 Jul '09

13 Jul '09

Hello: I have a problem using boost deadline timer that I cannot resolve. Why the resume method do not call again to the handler method??? Do I have something wrong? class TimerCallback { public: virtual void OnTimer()=0; }; class Timer : boost::noncopyable { public: Timer(unsigned long timeOutMilliSeconds, TimerCallback* callbac) : m_scheduler(), m_timer(m_scheduler), m_timerThread(), m_callbac(callbac), m_timeOutMilliSeconds(timeOutMilliSeconds) { }; virtual ~Timer() { m_scheduler.stop(); m_timerThread->join(); }; void some_operation() { //m_scheduler.post(boost::bind(m_callbac->OnTimer(), this)); m_callbac->OnTimer(); }; void handler(const boost::system::error_code& error) { if (!error) { // Timer expired. m_callbac->OnTimer(); m_timer.expires_from_now(boost::posix_time::milliseconds(m_timeOutMilliSeconds)); // Start an asynchronous wait. m_timer.async_wait(boost::bind(&Timer::handler, this, boost::asio::placeholders::error)); } } void start() { // Set an expiry time relative to now. m_timer.expires_from_now(boost::posix_time::milliseconds(m_timeOutMilliSeconds)); // Start an asynchronous wait. m_timer.async_wait(boost::bind(&Timer::handler, this, boost::asio::placeholders::error)); m_timerThread.reset(new boost::thread(boost::bind(&boost::asio::io_service::run, &m_scheduler))); } void pause() { m_timer.cancel(); }; void resume() { m_timer.expires_from_now(boost::posix_time::milliseconds(m_timeOutMilliSeconds)); m_timer.async_wait(boost::bind(&Timer::handler, this, boost::asio::placeholders::error)); }; private: boost::asio::io_service m_scheduler; boost::asio::deadline_timer m_timer; boost::scoped_ptr<boost::thread> m_timerThread; TimerCallback* m_callbac; unsigned long m_timeOutMilliSeconds; }; Salu2.. masch...

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building boost libraries for cross-compiled project
by Steve Drake 13 Jul '09

13 Jul '09

I am trying to use boost (specifically the regex part) in a cross-compiled environment. The target is a single board computer running Linux on ARM. My development computer is a Windows 2000 machine. The cross compiler is a GNU C++ compiler that I got from the SBC vendor. It is located here: c:\TechnologicToolchain\devel-tools\crosstool-cygwin\bin\arm-unknown-linux-g nu-g++.exe When I build my ARM application program, by PATH on the PC is set to this: c:\TechnologicToolchain\devel-tools\crosstool-win\bin; \ c:\TechnologicToolchain\devel-tools\crosstool-cygwin\bin; \ c:\TechnologicToolchain\devel-tools\cygwin How do I build the boost libraries on my development PC so I can link them with my cross-compiled application code and run them on the ARM target? I am unfamiliar with bjam so I am having trouble figuring out how to configure it to use a specific compiler executable. Thanks in advance for any suggestions. Steve

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Boost Python is slow?
by Tyomich on the AIR 13 Jul '09

13 Jul '09

Hello everyone! I'm currently embedding Python and have a problem. I have a struct (point) which looks like struct TPoint { int x, y; }; And I want it to be usable from Python. I made it in two ways: the first one was writing all the warpping by myself according to Python/C API, and the second was wrap it with Boost.Python. So it looks like class_<TPoint>("TPoint") .def_readwrite("x", &TPoint::x) .def_readwrite("y", &TPoint::y); It wraps ok but here is a problem: I create a huge (1000000 items) list of objects of that type: def cr_fig(n): res = [] while n>0: res.append(TPoint()) n -= 1 return res And then when I use a simple function which just increments the x member of every object, this function takes about 4 seconds to process the whole list (1000000 items) of Boost-wrapped objects and less than a second to process objects of my own wrapping! How this can be possible? Is Boost.Python much more slower than Python itself? Regards, Artyom Chirkov. P.S. I couldn't find out how to write to Boost.Python community, so I wrote here. If anyone knows how to do that, please let me know!

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[Thread] Can't suppress thread_specific_ptr 'memory leak'
by Joshua Boyce 13 Jul '09

13 Jul '09

Hey all, having a small issue with thread_specific_ptr. I'm a MSVC user and I'm getting a memory leak reported with the leak detection from _CrtSetDbgFlag and I was wondering if it was possible to suppress it somehow? I only ask because I know that these leaks in particular are false positives (or so it seems) and I wish to filter them out so I can quickly see each time if anything else is leaking without having to "manually" filter the log myself. Thanks.

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Re: [Boost-users] A question on data change with lambda expression. Can any one with kindness help me?
by fmingu 13 Jul '09

13 Jul '09

Can any experts with kindness help me? I really need the answer. I have tried my best to program with c++. And I want to be familiar with lambda. Thanks a lot.

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[phoenix] how to compare std:string
by Michael Caisse 12 Jul '09

12 Jul '09

Hi all - I have a vector of std::pair< std::string, int > and I want to use std::find_if to get the location where the std::pair first is some string value. I have successfully performed the correct incantation to compare the std::pair second to an int; however, it eludes me to what I need for the string. This is my test ---------------------------------- #include <vector> #include <algorithm> #include <boost/spirit/home/phoenix/core.hpp> #include <boost/spirit/home/phoenix/operator.hpp> #include <boost/spirit/home/phoenix/bind/bind_member_variable.hpp> int main() { using namespace boost::phoenix; using namespace boost::phoenix::arg_names; typedef std::pair< std::string, int > node_type; typedef std::vector< node_type > node_storage_type; node_storage_type my_nodes; my_nodes.push_back( std::pair< std::string, int >( "foo", 8 ) ); // this works great node_storage_type::iterator iter = std::find_if( my_nodes.begin(), my_nodes.end(), bind( &node_type::second, arg1 ) == 8 ); // compilation error here: ..\..\..\library\vendor\boost_1_38_0\boost/spirit/home/phoenix/operator/comparison.hpp(27) : error C2678: binary '==' : no operator found which takes a left-hand operand of type 'std::basic_string<_Elem,_Traits,_Ax>' (or there is no acceptable conversion) // iter = std::find_if( my_nodes.begin(), my_nodes.end(), bind( &node_type::first, arg1 ) == "foo" ); return 0; } Thanks ! michael -- ---------------------------------- Michael Caisse Object Modeling Designs www.objectmodelingdesigns.com

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playing around with tutorial codes to understand ioservice
by Ozgur Ozturk 11 Jul '09

11 Jul '09

Hi, I have been working on asio from the online documentation for more than a week but I am still confused about the io_service. Especially about what happens when we pass io_service to so many other things (timer, socket, chat_client etc.)? I hoped playing around with the codes in tutorial may help me in understanding. I modified the code a bit from timer3.cpp example<http://www.boost.org/doc/libs/1_39_0/doc/html/boost_asio/tutorial/tuttimer3…>. (modified code is in attachment) When I add another io_service object, I was thinking one would run then the other one would start since in the comments of io_service.hpp it says * The run() function blocks until all work has finished and there are no * more handlers to be dispatched, or until the io_service has been stopped. but when I run two io_service objects io.run(); io2.run(); I get output from two of them interchangingly. (first print in each line is address of deadline timer, I added in print function to see which thread is running.) 0012FF04 0 0012FEE4 1 0012FEE4 2 0012FEE4 3 0012FF04 4 Could someone help me understand io_service class? (Maybe some pointers to old discussions could help.) I also read some papers about Proactor pattern, without too much help. Maybe example code can be supplied with more comments. I would also appreciate suggestions and pointers (probably in private emails to ozgur7 AT gmail com) to help me about implementing a simple command server (proxy). I am trying to implement a server to accept clients and run MySQL queries (example: look up name and password pair in a table) and pass results to clients. I am using connector/C++ for MySQL part, and that part seems very easy. However I am having difficulty in understanding asio. Do you think, I am overkilling for such a simple thing. (I thought it could pay back later when I needed to improve my program...) Thanks in advance, Best regards, Ozgur (Oscar) Ozturk www.DrOzgur.com +1 (614) 805-4370

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