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Re: [Boost-users] Collecting boost multi-index meta data
by Joaquin M Lopez Munoz 25 Mar '11

25 Mar '11

Gokulakannan Somasundaram <gokul007 <at> gmail.com> writes: > > > Hi, > Say i have a boost::tuple / MPL Sequence, on which i have > created a multi-index. Is it possible for me collect all the > attribute numbers on which i have declared the > IndexSpecifierList( the one passed as template parameter to > boost::multi_index::indexed_by ) ? Hi Gokul, I'm not sure I undersand your question. Have you taken a look at the index_type_list nested type? http://www.boost.org/libs/multi_index/doc/reference/multi_index_container.h… types >From this MPL sequence you can easily extract the list of key extractor types used for defining the multi_index_container, which hopefully is close to what you're after. Don't hesitate to elaborate a little more on your question and I'll see whether I can be more helpful. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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Math/Statistical Distributions
by Andrej van der Zee 25 Mar '11

25 Mar '11

Hi, Statistics have been a while ago... I was reading the documentation, at least part of it, of the Boost library Math/Statistical Distributions. But I think I need a bit of help... I have many values Yi that are closely distributed around a mean value Y-mean. The collection of Yi is obtained by an algorithm that sometimes produces trash values that need to be discarded. Such false values are typically not "close" to the Y-mean. I was hoping somebody could tell what distribution I should use and how I should use this. If I recall correctly from my school-days, I need the Normal (Gaussian) Distribution. What would be the algorithm to find those trash values? Thank you, Andrej

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Serialization: multiple definition of 'boost::archive::detail::init_guid...
by Marco Piacentini 25 Mar '11

25 Mar '11

Hi guys...I've found on google some people with the same problem, but all of them have a partial solution... In practice this error happens where I include a .h file which contain the directive #include <boost/archive/text_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> and the macro BOOST_CLASS_EXPORT() in more than one .cpp file... I have the necessity to serialize/deserialize in more than one .cpp file and at these points I have to include the .h which contains the polymorphic struct that I have to serialize/deserialize. So the partial solution proposed from others to put all the the include in a single file, is not praticable for me.. Do you know another solution?thank you very much... Bye..

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Boost Threads are not parallel
by Panagiotis Foteinos 25 Mar '11

25 Mar '11

Hello users. I observed the boost threads behave strangely, depending on the way I call the function to be executed in parallel. In the following example (example #1), the threads launched are executed in parallel: **************************************************************************************** 1) class Test { int insert(){}; } object; boost::thread* threads = new boost::thread[N]; for(unsigned int i = 0; i < N; i++) { threads[i] = boost::thread(&Test::insert, &object); } **************************************************************************************** However, in the following example (example #2), the threads are executed sequentially. Only the line in the for-loop body differs from example#1. **************************************************************************************** 2) class Test { int insert(){}; } object; boost::thread* threads = new boost::thread[N]; int ret; for(unsigned int i = 0; i < N; i++) { threads[i] = boost::thread(boost::lambda::var(ret) = object.insert()); } **************************************************************************************** Can anybody explain why the threads in example#2 are executed sequentially (i.e., one at a time)? Best Regards, Panagiotis Foteinos

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io_service::stop() call safe from within post()ed functor?
by Dom Driver 25 Mar '11

25 Mar '11

Hi guys, Picture a server class with the following methods (pseudocode): void Server::Work() { // Start the Async receive. mSocket.async_receive_from( *blah* ) ); // Start the Async IO service. mASIOService.run(); } void Server::Start() { // Launch a new thread to do the work. mThread = boost::thread( boost::bind( &Server::Work, this ) ); } void Server::Stop() { // Post the stop request to the io_service. mASIOService.post( boost::bind( &Server::DoStop, this ) ); // Join the comms thread. mThread.join(); } void Server::DoStop() { // Actually stop the io_service. mASIOService.stop(); } Assuming handling of packets is all correctly implemented, is it safe for the user to simply call the Stop() object method to stop the server? Basically, can a function that's been post()ed to an io_service call io_service.stop() for that io_service? TIA, Dom

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[iostreams] Can I apply different char_type on a chain of filters?
by 甜瓜 25 Mar '11

25 Mar '11

Hi, all, I usually want to read a file, and group the bytes into some object (eg: struct MyData) for further use. boost::iostreams provides the filtering_stream, but it seems all filters along the chain MUST have the same char_type. Is there a way that transform a byte stream into MyData stream? eg: ifstream file("d.gz", ios_base::in | ios_base::binary); filtering_streambuf<input> in; in.push(MyDataExtractor()); in.push(gzip_decompressor()); in.push(file); class MyDataExtractor { public: typedef MyData char_type; struct category ...; template<typename Source> std::streamsize read(Source& src, char_type* s, std::streamsize n) {...} }; Thank you in advance! -- melon

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[BOOST Interprocess] file lock error on MSVC 10
by Claude 24 Mar '11

24 Mar '11

Hi, I'm trying to compile simple program with MSVC++ 10 that use <boost/interprocess/sync/file_lock.hpp> include file (boost version 1.44) But I have a compile error in this file at row 68: C:\Users\Claudio\Desktop\boost_1_44_0\boost/interprocess/sync/file_lock.hpp(68): vedere il riferimento all'istanza del modello di funzione 'boost::interprocess::file_lock &&boost::interprocess::move<boost::interprocess::file_lock&>(T)' in corso di compilazione with [ T=boost::interprocess::file_lock & ] "Impossibile associare un elemento lvalue a un riferimento di rvalue" ("Can not associate a lvalue to a rvalue reference") This program compiles without error on GCC 4.5 (Linux Ubuntu) Why? -- View this message in context: http://boost.2283326.n4.nabble.com/BOOST-Interprocess-file-lock-error-on-MS… Sent from the Boost - Users mailing list archive at Nabble.com.

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Boost gregorian date time from preformated string
by Louis Hoefler 24 Mar '11

24 Mar '11

I use boost 1.46.0 and visual studio 2010. I try to convert a string into a date time object. I found some examples that use stringstreams. Is it possible to convert custom formatted date/time strings into gregorian date objects without using a stringstream? Thank you, Louis

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Re: [Boost-users] Thread Interruption Best Practice
by Dom Driver 24 Mar '11

24 Mar '11

> if I understand your problem you want the thread blocking in select to return? Correct. I need this call to return when: 1) I've got some data waiting to be read. 2) The application is terminating and I want to stop my RX communications thread. The first one is straightforward. I'll investigate the use of pipes as a secondary option. As for 2), from other suggestions, I've gone back to the ASIO library. I read about slushies and brain-freeze, and thought it might be the way to go. However, I think I've managed to fall victim to brainfreeze myself. >From the ASIO example at: http://www.boost.org/doc/libs/1_46_1/doc/html/boost_asio/example/echo/async… This is an asynchronous server similar to what I'm trying to do here. I've got a couple of questions on this, 1) When the server object is created, the call to socket.async_read_from() is made immediately. If there is no data waiting, to be read, this call returns immediately, right? 2) When data does arrive, the handler 'handle_receive_from()' is called. Regardless of whether some bytes are read or not, we eventually call socket.async_read_from() again. This is probably quite fundamental to what I'm misunderstanding, but doesn't this mean I'll be effectively calling socket.async_read_from() from within the handler of a call to socket.async_read_from()? Will I be recursing indefinitely until the application terminates? That doesn't sound right, so I must be missing something very obvious here. Hmmm. Biblical-style ray-of-light guidance appreciated!

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Project using Boost won't build with Xcode 4; complains about "global weak symbols"
by G S 23 Mar '11

23 Mar '11

Hi all. I'm using Boost in an iPhone app as a statically linked lib, and after updating to Xcode 4 the project won't build. It fails with this: *ld: bad codegen, pointer diff in boost::system::error_category:* *:error_category()to global weak symbol vtable for boost::system::error_**categoryfor architecture i386* Happens for both simulator and device, after the same project built fine under previous Xcodes. Anybody have some insight on this and a solution? Thanks! Gavin

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