July 2015 - Boost-users - lists.boost.org

Subgraph at distance n
by Rossano Schifanella 14 Jul '15

14 Jul '15

Hi all, which is the easiest way to extract from a graph G and a generic node source a subgraph with all the vertices/edges at distance at most n from source? Thanks a lot for your help. Best, Rossano

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Boost.DLL Review is finished
by Vladimir Prus 14 Jul '15

14 Jul '15

Boosters, the formal review of the Boost.DLL library by Antony Polukhin is now finished. The preliminary results are as follows: The following people have provided reviews: - Ralf Globisch - Yes - Klaim - Joël Lamotte - Yes (*) - Niall Douglas - Yes, conditionally - John P Fletcher - Yes - Bjorn Reese - Yes - Edward Diener - Yes Klaim - Joël has asked that his vote is not counted until he's done trying the library for real, and there was no confirmation it's done yet. The following people have contributed, but did not provide a review - Rodrigo Madera - Thomas Trummer - Rob Stewart - Ion Gaztañaga If anybody would like to amend or clarify anything, or plans to provide additional comments during this week, please contact me off-list. I will post final review result after that. Thanks, Volodya

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Platform checks fail on Centos 6 after bootstrap ?
by gabriel nützi 12 Jul '15

12 Jul '15

Hello all :-) Is somebody able to help with the following problem: http://stackoverflow.com/questions/31347026/boost-build-on-centos-6-5-faile… <http://stackoverflow.com/questions/31347026/boost-build-on-centos-6-5-faile…> boost 1.58 used I dont know why platform checks are not done correctly? Thanks a lot!

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[Boost-announce] [boost] [review] Metaparse Review Result
by Christophe Henry 11 Jul '15

11 Jul '15

Hi all, First of all, the final result. Metaparse is formally unconditionally accepted into Boost. We had 11 reviews, all "Yes" votes. 2 "No" reviews based on formality were later reversed to a "Yes". The review was lively, with a general agreement that the library is very useful, the design of high quality and the documentation great. Here are some noticeable quotes which helped me take my decision: - "thank you Abel for submitting such an amazing library. The quality of the documentation and code is wonderful and it has been a pleasure to review Metaparse." (Michael Caisse) - (Design) "Of high quality. Based on the MPL paradigm, but I don't view this as a problem." (Peter Dimov) - "Part of the role of boost is to push compilers to the limit (and sometimes beyond). This library certainly has the capabilities to do so." (Roland Bock) Worth noticing is the review of Gordon Woodhull. I myself wrote a new front-end for MSM using Metaparse, and other use cases were very welcome and Gordon managed to produce one for his compile-time graph library by the end of the review, which I found impressive (for both the reviewer and the library). Thank you for investing time in this review. Another important factor for me for acceptance is how well the author is going to maintain his library. We have too many abandoned libraries. Abel went out of his way to oblige remarks and demands made by reviewers. Long before the reviews he also had obliged my many critics and demands. He also showed himself open for experiments. All this while keeping a very calm and professional tone. This is for me a very good sign of a library which will be well-maintained. Finally, there were some repeated important comments which I see as adressed to the rest of Boost that the library is targeted towards library writers. >From Peter Dimov: > - Are you knowledgeable about the problem domain? "I'm not sure if anybody is. :-)" It all depends on us, library and potential library writers to become knowledgeable about this domain and make this library move from potentially useful to very useful. We need to use it to write more cool libraries. I notice a recurring theme where Boost would be dead or on the way to doom etc etc. Some very popular Boost libraries are now part of the Standard, and so what? We need to make new ones. Metaparse is one of them. Let's build more, using it! Yes Reviews(11): Andrzej Krzemienski Bjorn Reese Gordon Woodhull Lee Clagett Louis Dionne Michael Caisse Paul A. Bristow Peter Dimov Roland Bock Edward Diener Niall Douglas I want to thank all the reviewers who invested their time in this review and those who provided some usefuls comments. I also want to thank Abel for presenting this great library. Christophe Henry Metaparse Review Manager

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Slow decoding in thread
by Gonzalo Garramuno 10 Jul '15

10 Jul '15

I am writing a movie player using boost. I use a condition_variable to control a mutex in one thread that waits for packets of video to be ready for decoding, while another thread feeds those packets. My problem is that the decode thread may end up doing a lot of work when playing backwards and it is not ready to wait on the condition variable when the message comes from the other thread and so it hangs (or so I think). This is my wait loop. I apologize for the use of macros. #define SCOPED_LOCK(mutex) Mutex::scoped_lock lk_##mutex(mutex) #define CONDITION_WAIT( cond, mutex ) cond.wait( lk_##mutex ); void aviImage::wait_image() { mrv::PacketQueue::Mutex& vpm = _video_packets.mutex(); SCOPED_LOCK( vpm ); for(;;) { if ( stopped() || ! _video_packets.empty() ) break; CONDITION_WAIT( _video_packets.cond(), vpm ); } return; } When it returns it tries to decode one or more frames of video taken from _video_packets. The condition variable is notified whenever the program calls push_back() to add a packet. That is: class PacketQueue { .... inline void push_back( AVPacket& pkt ) { Mutex::scoped_lock lk( _mutex ); // assert( pkt.dts != MRV_NOPTS_VALUE ); if ( av_dup_packet(&pkt) < 0 ) { std::cerr << "Could not duplicate packet - not added" << std::endl; return; } _packets.push_back( pkt ); _bytes += pkt.size; _cond.notify_one(); } }; Can somebody suggest an alternative to this scheme? -- Gonzalo Garramuño

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Query: metis_input_exception
by Mayank Bakshi 10 Jul '15

10 Jul '15

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crc updating how?
by U.Mutlu 09 Jul '15

09 Jul '15

Hi, I need to calc the crc chunkwise (ie. calc crc of a block, then continue with the next block etc.). Is this (not) possible with the boost crc? In other words: how can the type "crc_32_type" be initialized with a user supplied uint32_t value? boost::crc_32_type crc; crc = 0x1234; // <-- this brings compile error crc.process_bytes(buf, len); error: no match for ‘operator=’ (operand types are ‘boost::crc_32_type {aka boost::crc_optimal<32ul, 79764919u, 4294967295u, 4294967295u, true, true>}’ and ‘const uint32_t {aka const unsigned int}’) Thx

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[crc] bug in boost::crc
by U.Mutlu 09 Jul '15

09 Jul '15

/* boost-crc-bug-demo.cpp Written by U.Mutlu on 2015-07-09-Th Compile: g++ -O2 -Wall -std=gnu++11 boost-crc-bug-demo.cpp Run: ./a.out Output: crc("The quick brown fox jumps over the lazy dog")=414fa339 crc("The quick brown fox ")=88b075e2 crc("The quick brown fox jumps over the lazy dog")=4ac56d0f ERROR See also: http://www.boost.org/doc/libs/1_58_0/libs/crc/crc.html#usage Conclusion: It doesn't do what it should and also advertises; ie. there's a bug */ #include <boost/crc.hpp> #include <boost/cstdint.hpp> #include <iostream> int main() { uint32_t expected; { const std::string sTxt = "The quick brown fox jumps over the lazy dog"; boost::crc_optimal<32, 0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true, true> crc; crc.process_bytes(sTxt.data(), sTxt.size()); std::cout << "crc(\"" << sTxt << "\")=" << std::hex << crc.checksum() << std::endl; // save the result for the following test expected = crc.checksum(); } // test: doing the same as above, but now in 2 steps, ie. chunk- or blockwise: std::string sTxt; uint32_t result = 0xFFFFFFFF; for (size_t i = 0; i <= 1; ++i) { sTxt += !i ? "The quick brown fox " : "jumps over the lazy dog"; // using the special ctor for initial remainder stored in "result" boost::crc_optimal<32, 0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true, true> crc(result); crc.process_bytes(sTxt.data(), sTxt.size()); std::cout << "crc(\"" << sTxt << "\")=" << std::hex << crc.checksum() << std::endl; result = crc.checksum(); } // eval: const std::string sRes = result == expected ? "SUCCESS" : "ERROR"; std::cout << sRes << std::endl; return 0; }

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[Interprocess] posix robust mutex and EOWNERDEAD
by Malko 07 Jul '15

07 Jul '15

Hi, I lurked a bit and found this: http://boost.2283326.n4.nabble.com/boost-interprocess-gt-1-45-robust-mutexe… I didn't feel like necroposting, and it's /dev anyway, so allow me to ask here about updates on the matter. Is there anything, even if only "experimental" or "beta", that you have that would allow me to handle the EWOENERDEAD result? I'd rather use your code before putting my hands on your library, since it would be easier to let my manager (and his manager) deal with a "boost beta" rather than my personal modification to boost. If there is none, I would really need to modify your files for my project to work, and I would appreciate if you could confirm a couple of things for me. In http://stackoverflow.com/a/1179766/4598277 it is mentioned to modify two files: 1. posix/thread_helpers.hpp to set the attribute (first time ever I was happy to get an exception :D) 2. posix/mutex.hpp to handle the EOWNERDEAD return value Can you please confirm if this would be enough? It would seem so to me, but I have only studied parts of your code. Thank you for the assistance. -- View this message in context: http://boost.2283326.n4.nabble.com/Interprocess-posix-robust-mutex-and-EOWN… Sent from the Boost - Users mailing list archive at Nabble.com.

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iterator over boost::tuple
by Uthpal Urubail 06 Jul '15

06 Jul '15

Experts, What is the best way to iterator over boost::tuple and return value? Example: For(int i=0;i<boost::tuples::length<T>::value;i++) { Boost_tuple_example.get<i>(); } Regards, UJ

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