June 2013 - Boost - lists.boost.org

Status of various Boost initiatives?
by Robert Ramey 21 Jul '13

21 Jul '13

I'm trying to get a handle on the current state of the various boost migrations which have been underway. a) migration to GIT b) migration to CMake c) status of rypll when I try to track this down I find many dead links, repeated information. I also don't find some blogs I used to be able to find on these subjects. Anyone up to provide an current status snapshot? Robert Ramey

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A more convenient Variant visitation syntax
by Kevin Wu Won 19 Jul '13

19 Jul '13

While Boost Variant is a wonderful library that fills a genuine hole in the C++ language, it is not as nice to use as it could be. The "correct" way to unwrap a variant is to apply a static visitor, but this method carries a high syntactic burden because it needs the user to define a class (probably somewhere far away) just so they can "switch" on the type of the object stored in the variant. I came up with a solution where the handler functions can be specified inline with C++11 lambdas. Here's an example: boost::variant< int, std::string > u("hello world"); int result = match(u, [](int i) -> int { return i; }, [](const std::string & str) -> int { return str.length(); }); The `match` function accepts the variant followed by the handler functions. The functions can be specified in any order. It will fail to compile if the functions do not match the types of the variant, if the return types are not all the same, or if a non-unary function is supplied. This is C++11 only because it's quite pointless without lambda functions. I've tested it with gcc 4.7. It doesn't work on gcc 4.6, which can't handle the variadic templates. Here's the code: https://github.com/exclipy/inline_variant_visitor What do you think? This started out for me as an exercise to learn template metaprogramming and C++11, but hopefully, it can actually evolve into something useful.

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Git Modularization example Boost .gitattributes
by Niall Douglas 16 Jul '13

16 Jul '13

> > Shouldn't the repositories contain a .gitattributes file indicating the > > eol flavor to be used for text files where it has significance? > > Perhaps! I don't know anything about .gitattributes. Where can I find > out more? Dave, I can probably save you some work here with my "perfect" mirror of Boost's EOL and MIME type config into a .gitattributes with which I configured my subgit to mirror my git repo into Boost sandbox. Taken from https://github.com/ned14/TripleGit/blob/master/.gitattributes: * text=auto !eol svneol=native#text/plain *.gitattributes text svneol=native#text/plain # Scriptish formats *.bat text svneol=native#text/plain *.bsh text svneol=native#text/x-beanshell *.cgi text svneol=native#text/plain *.cmd text svneol=native#text/plain *.js text svneol=native#text/javascript *.php text svneol=native#text/x-php *.pl text svneol=native#text/x-perl *.pm text svneol=native#text/x-perl *.py text svneol=native#text/x-python *.sh eol=lf svneol=LF#text/x-sh configure eol=lf svneol=LF#text/x-sh # Image formats *.bmp binary svneol=unset#image/bmp *.gif binary svneol=unset#image/gif *.ico binary svneol=unset#image/ico *.jpeg binary svneol=unset#image/jpeg *.jpg binary svneol=unset#image/jpeg *.png binary svneol=unset#image/png *.tif binary svneol=unset#image/tiff *.tiff binary svneol=unset#image/tiff *.svg text svneol=native#image/svg%2Bxml # Data formats *.pdf binary svneol=unset#application/pdf *.avi binary svneol=unset#video/avi *.doc binary svneol=unset#application/msword *.dsp text svneol=crlf#text/plain *.dsw text svneol=crlf#text/plain *.eps binary svneol=unset#application/postscript *.gz binary svneol=unset#application/gzip *.mov binary svneol=unset#video/quicktime *.mp3 binary svneol=unset#audio/mpeg *.ppt binary svneol=unset#application/vnd.ms-powerpoint *.ps binary svneol=unset#application/postscript *.psd binary svneol=unset#application/photoshop *.rdf binary svneol=unset#text/rdf *.rss text svneol=unset#text/xml *.rtf binary svneol=unset#text/rtf *.sln text svneol=native#text/plain *.swf binary svneol=unset#application/x-shockwave-flash *.tgz binary svneol=unset#application/gzip *.vcproj text svneol=native#text/xml *.vcxproj text svneol=native#text/xml *.vsprops text svneol=native#text/xml *.wav binary svneol=unset#audio/wav *.xls binary svneol=unset#application/vnd.ms-excel *.zip binary svneol=unset#application/zip # Text formats .htaccess text svneol=native#text/plain *.bbk text svneol=native#text/xml *.cmake text svneol=native#text/plain *.css text svneol=native#text/css *.dtd text svneol=native#text/xml *.htm text svneol=native#text/html *.html text svneol=native#text/html *.ini text svneol=native#text/plain *.log text svneol=native#text/plain *.mak text svneol=native#text/plain *.qbk text svneol=native#text/plain *.rst text svneol=native#text/plain *.sql text svneol=native#text/x-sql *.txt text svneol=native#text/plain *.xhtml text svneol=native#text/xhtml%2Bxml *.xml text svneol=native#text/xml *.xsd text svneol=native#text/xml *.xsl text svneol=native#text/xml *.xslt text svneol=native#text/xml *.xul text svneol=native#text/xul *.yml text svneol=native#text/plain boost-no-inspect text svneol=native#text/plain CHANGES text svneol=native#text/plain COPYING text svneol=native#text/plain INSTALL text svneol=native#text/plain Jamfile text svneol=native#text/plain Jamroot text svneol=native#text/plain Jamfile.v2 text svneol=native#text/plain Jamrules text svneol=native#text/plain Makefile* text svneol=native#text/plain README text svneol=native#text/plain TODO text svneol=native#text/plain # Code formats *.c text svneol=native#text/plain *.cpp text svneol=native#text/plain *.h text svneol=native#text/plain *.hpp text svneol=native#text/plain *.ipp text svneol=native#text/plain *.tpp text svneol=native#text/plain *.jam text svneol=native#text/plain *.java text svneol=native#text/plain Hope that's useful. Niall --- Opinions expressed here are my own and do not necessarily represent those of BlackBerry Inc.

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Git Modularization hiccups
by Beman Dawes 15 Jul '13

15 Jul '13

* "git clone --recursive http://github.com/boostorg/boost modular-boost" is mostly working fine here (on Win7) but is producing one set of error messages: Cloning into 'libs/assign'... fatal: reference is not a tree: 57ec5d1534810090649b18c88e66a46f48cdcf1c ... Unable to checkout '57ec5d1534810090649b18c88e66a46f48cdcf1c' in submodule path 'libs/assign' The remaining hiccups are in the root directory, comparing trunk to master: * boost.css is missing content from revisions 36243 and 53553. * boost-build.jam has different comments and history. Something is totally whacky. * boostcpp.py contents are the same, but the trunk file has Unix line endings, the master file has Windows line endings. * Same problem with bootstrap.sh. IIRC, it is important that the .sh files have the Unix line endings. * c++boost.gif not present in trunk, present in master. * index.html missing in master. * Jamfile.v2 and Jamroot.jam not present in trunk, present in master. * INSTALL missing in master. * LICENSE_1_0.txt has Unix line endings in trunk, Windows line endings in master. * project-config.jam missing in master. * rst.cc missing in master. * README.txt not present in trunk, present in master. HTH, --Beman

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[filesystem] Please take care of #8706
by Antony Polukhin 10 Jul '13

10 Jul '13

Hi, There is a ticket https://svn.boost.org/trac/boost/ticket/8706 and patch in it that fixes compilation of Boost.Filesystem under Android NDK. Tested patch under latest NDK and it works well. Fix is required to start regression tests for droid platform. -- Best regards, Antony Polukhin

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Re: [boost] [utility][thread] result_of - erroneous result type from a C++11 lambda
by Klaim - Joël Lamotte 04 Jul '13

04 Jul '13

On Tue, Apr 2, 2013 at 7:16 PM, Vicente J. Botet Escriba < vicente.botet(a)wanadoo.fr> wrote: > I've started to use C++11 lambda functions with Boost.Thread. > > The following works with clang-3.2 > > boost::future<int> f1 = boost::async( []() -> int {return 123;} ); > > > But it fails with gcc-4.6.2, 4.7.2 and 4.8.0 > > ../example/lambda_future.cpp:**25:91: erreur: conversion from > ‘boost::future<void>’ to non-scalar type ‘boost::future<int>’ requested > boost::future<int> f1 = boost::async( []() -> int {return 123;} ); > > The current implementation of boost::async uses boost::result_of to get > the result type of the callable parameter. > > Is this a know bug on boost::result_of or gcc compiler? > I'm seeing exactly the same behaviour in *VS2012 Update 2*. I'm using Boost 1.54.0 beta *r84748* To be more precise: 1) I first was just using boost::future and tried to use the new .then(), here is a full repro: #include <boost/thread/future.hpp> auto ft = boost::async( []{ return 42; } ).then( []( boost::future<int> r ){ return 666; } ); This fails because boost::async() returned a future<void> instead of a future<int>. I suspect the then() call to have the same problem. I can provide the full error log but I think it's not that useful. 2) Just to be sure I tried this full test: #include <boost/thread/future.hpp> int main() { auto ft = boost::async( []{ return 42; } ); // SUCCEED: static_assert( std::is_same< decltype(ft), boost::future<void> >::value, "WTF???" ); // FAILS: static_assert( std::is_same< decltype(ft), boost::future<int> >::value, "Not the expected type!" ); } Both asserts confirm that I don't get what I want. 3) I remembered that there were some issues from usage of boost::result_of in Boost.Log, so to clarify the situation I setup the following full test: #include <boost/utility/result_of.hpp> #include <type_traits> int top() { return 42; } struct K { int operator()(){ return 42; } typedef int value_type; }; auto F = []{ return 42; }; int main() { // A: ALL SUCCEED static_assert( std::is_same< decltype(K()()), int >::value, "Not the expected type!" ); static_assert( std::is_same< decltype(top()), int >::value, "Not the expected type!" ); static_assert( std::is_same< decltype(F()), int >::value, "Not the expected type!" ); // B: ALL SUCCEED static_assert( std::is_same< std::result_of<K()>::type, int >::value, "Not the expected type!" ); static_assert( std::is_same< std::result_of<decltype(top)>::type, int >::value, "Not the expected type!" ); static_assert( std::is_same< std::result_of<decltype(F)()>::type, int >::value, "Not the expected type!" ); // C: ALL SUCCEED std::result_of<K()>::type a = K()(); std::result_of<decltype(top)>::type b = top(); std::result_of<decltype(F)()>::type c = F(); // D: ALL FAILS static_assert( std::is_same< boost::result_of<K()>::type, int >::value, "Not the expected type!" ); static_assert( std::is_same< boost::result_of<decltype(top)>::type, int >::value, "Not the expected type!" ); static_assert( std::is_same< boost::result_of<decltype(F)()>::type, int >::value, "Not the expected type!" ); // E: ALL FAILS boost::result_of<K()>::type d = K()(); // error C2182: 'd' : illegal use of type 'void' boost::result_of<decltype(top)>::type e = top(); // error C2182: 'e' : illegal use of type 'void' boost::result_of<decltype(F)()>::type f = F(); // error C2182: 'f' : illegal use of type 'void' } This shows clearly that: 1. boost::result_of don't behave like std::result_of on this platform (and from previous discussions, on other platforms too). 2. both std::result_of and decltype() provide the result I expect from reading documentations about these. So far I'm assuming that the problem really is from boost::result_of, but I might be wrong because the differences with std::result_of are not clear to me. ---- Unfortunately this makes future.then() unusable if we expect return types. I don't know if it impacts other libraries (I suspect Boost.Log). Should I report a bug or is it known, already fixed or a misuse? Joel Lamotte

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[result_of] Documentation update for ticket 7753
by Nathan Crookston 04 Jul '13

04 Jul '13

Hi Daniel & all, I'm updating the patch for ticket 7753 ( https://svn.boost.org/trac/boost/ticket/7753) I've made the requested changes to the patch, but I had a question on how to best explain which macro to define if, for example, you want result_of to work with C++11 lambdas. In the past, users with a pre-N3276 decltype have been advised to just #define BOOST_RESULT_OF_USE_DECLTYPE, with the explanation that "it's probably just going to work." While that advice is true, there are cases where this doesn't work; hence the addition of BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK. To explain why you'd define the FALLBACK macro over the USE_DECLTYPE macro, I'm thinking of including a paragraph like the following. "The question naturally arises on why have both BOOST_RESULT_OF_USE_DECLTYPE and BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK. In many situations, BOOST_RESULT_OF_USE_DECLTYPE will work well, even with pre-N3276 decltype. However, there are cases where a post-N3276 decltype is required to correctly deduce the return type of a functor. If a translation unit includes a functor whose return type is only deducible with TR1 or a post-N3276 decltype, using result_of with, e.g. a C++11 lambda function, will fail without BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK. If the macro BOOST_NO_CXX11_DECLTYPE_N3276 is defined and BOOST_NO_CXX11_DECLTYPE is not defined when including result_of.hpp, defining BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK is the safest option that will allow you to deduce C++11 lambda return types." My question is, am I over explaining it? Of course, I'd rather have BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK defined automatically for compilers like VC10, g++4.5, etc., and include text like the following: "If you rely on the result of calling a nullary functor to be void, regardless of the actual return type, or if your code is not written to handle cases other than BOOST_RESULT_OF_USE_TR1 and BOOST_RESULT_OF_USE_DECLTYPE, you may wish to explicitly define one of those symbols prior to including result_of." Either way, comments welcome. Thanks, Nate

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[Serialization] Constructor for polymorphic archives
by Bjorn Reese 03 Jul '13

03 Jul '13

I have a set of my own Boost.Serialization archives (e.g. [1]) that I wish to write polymorphic variants of. I have tried to follow the blueprint from polymorphic_text_iarchive, which inherits from polymorphic_iarchive_route. The problem is that the constructor of my archives takes iterators (begin and end) as arguments, but the polymorphic_iarchive_route constructor expects a std::stream argument. Is there any workaround for this? [1] http://sourceforge.net/p/protoc/code/ci/master/tree/include/protoc/transenc…

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Any interest in bitstream class?
by Paul Long 02 Jul '13

02 Jul '13

Same semantics as, e.g., stringstream, but it operates on binary data. I already have the analogues to istringstream/stringbuf (you can take a look at ibitstream/bitbuf at https://github.com/dplong/bstream) There are some interesting features, but I won't go into them here. If there is interest, I would implement obitstream and bitstream and possibly support Boost::dynamic_bitset. The rationale is _succinct_ expression of predictive parsing of binary data. I've used ibitstream in production code for decoding RTP headers and frames of various video encodings. Below is a simple function that decodes an RTP header using ibitstream; I also have a GitHub repo that contains more complex code for high-level parsing of H.264 frames at https://github.com/dplong/rtspudph264 struct RtpHeader { bool padding, marker; bitset<7> payloadType; WORD sequenceNumber; DWORD timestamp, ssrcIdentifier; vector<DWORD> csrcIdentifier; struct { bool present; WORD identifier; vector<BYTE> contents; } extension; }; bool ParseRtpHeader(const BYTE *buffer, RtpHeader &rtp) { ibitstream bin(buffer); static const bitset<2> version(0x2); bitset<4> csrcCount; WORD extensionLength; bin >> version >> rtp.padding >> rtp.extension.present >> csrcCount >> rtp.marker >> rtp.payloadType >> rtp.sequenceNumber >> rtp.timestamp >> rtp.ssrcIdentifier >> setrepeat(csrcCount.to_ulong()) >> rtp.csrcIdentifier; if (rtp.extension.present) { bin >> rtp.extension.identifier >> extensionLength >> setrepeat(extensionLength * sizeof(DWORD)) >> rtp.extension.contents; } return bin.good(); }

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Static initialization of boost shared objects question
by Juan Carlos Franzoy 02 Jul '13

02 Jul '13

Hello. Thanks for reading my question. I fell into a deadlock in static initialization of boost shared objects. The deadlock occurs in a reentrant call to a function which contains a definition of a static variable. Apparenlty gcc protects the initialization of such variables with a condition variable. Looking at the c++ code nothing at all make anybody suspect about reentrancy. My "interpretation of the fact" may be titled 'something in gcc, ld, ld.so, c++language made the call to be reentrant' - There is a function boost::system::generic_category() that has a static variable V - V type is boost::system::annonymous-namespace::generic_error_category - boost::system::annonymous-namespace::generic_error_category is subclass of boost::system::error_category. - boost::system::annonymous-namespace::generic_error_category has no declared/defined constructor as well as all its superclasses - The compilation process generate the constructor boost::system::error_category::error_category() as a weak symbol inside every shared object that uses it. - There is a static variable boost::system::posix_category in one of the shared objects that is initialized calling boost::system::generic_category(). - when the static initialization of a shared object boost::system::posix_category get initialized - which calls boost::system::generic_category() - Inside boost::system::generic_category() starts the initialization of V which calls boost::system::error_category::error_category() - It may happend that the runtime calls an instance of boost::system::error_category::error_category() that resides in a shared object that is still not loaded - So that .so get loaded and it is called its own static initialization - which can call boost::system::generic_category() - BOOM I would love if you can confirm of refute my humble "interpretation". Details follows ------------------- boost version: 1-52-0 Operating system: uname -a SunOS bcpp-solaris10 5.10 Generic_147441-25 i86pc i386 i86pc $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/export/home/local/gcc-4.6.2/libexec/gcc/i386-pc-solaris2.10/4.6.2/lto-wrapper Target: i386-pc-solaris2.10 Configured with: ../src/gcc-4.6.2/configure --prefix=/export/home/local/gcc-4.6.2 --with-gmp=/export/home/local/gcc-4.6.2/gmp-4.3.2 --with-mpfr=/export/home/local/gcc-4.6.2/mpfr-3.0.0 --with-mpc=/export/home/local/gcc-4.6.2/mpc-0.8.2 --with-libelf=/export/home/local/gcc-4.6.2/libelf-0.8.12 --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --enable-languages=c,c++ --with-as=/usr/local/bin/as --with-gnu-as --with-ld=/usr/ccs/bin/ld --without-gnu-ld --enable-plugin --enable-multilib --enable-version-specific-runtime-libs --enable-bootstrap --enable-ssp --enable-libssp --with-included-gettext --enable-lto --host=i386-pc-solaris2.10 --build=i386-pc-solaris2.10 Thread model: posix gcc version 4.6.2 (GCC) Callstack backtrace (lines begining with = are my comments): = = deadlock here: the threads is waiting itself = #0 0xfd459019 in __lwp_park () from /lib/libc.so.1 #1 0xfd45365e in cond_sleep_queue () from /lib/libc.so.1 #2 0xfd453817 in cond_wait_queue () from /lib/libc.so.1 #3 0xfd453b94 in cond_wait_common () from /lib/libc.so.1 #4 0xfd453d02 in _cond_wait () from /lib/libc.so.1 #5 0xfd453d2d in cond_wait () from /lib/libc.so.1 #6 0xfd453d66 in pthread_cond_wait () from /lib/libc.so.1 #7 0xfd632898 in __gthread_cond_wait (g=0xfd822ea8) at ...build-gcc/out/i386-pc-solaris2.10/libstdc++-v3/include/i386-pc-solaris2.10/bits/gthr-default.h:846 #8 __gthread_cond_wait_recursive (g=0xfd822ea8) at ...work/build-gcc/out/i386-pc-solaris2.10/libstdc++-v3/include/i386-pc-solaris2.10/bits/gthr-default.h:860 #9 __gnu_cxx::__cond::wait_recursive (g=0xfd822ea8) at ...build-gcc/out/i386-pc-solaris2.10/libstdc++-v3/include/ext/concurrence.h:377 #10 __cxa_guard_acquire (g=0xfd822ea8) at .../src/gcc-4.6.2/libstdc++-v3/libsupc++/guard.cc:289 = = Reentrant call to boost::system::generic_category() = #11 0xfd812313 in boost::system::generic_category () at libs/system/src/error_code.cpp:425 #12 0xfe85cd38 in __static_initialization_and_destruction_0(__initialize_p=1, __priority=65535) at ./boost/system/error_code.hpp:214 #13 0xfe85d05f in _GLOBAL__sub_I_instantiate_re2c_lexer_str.cpp () at libs/wave/src/instantiate_re2c_lexer_str.cpp:56 = = static initization of boost.wave library = #14 0xfe8868fd in __do_global_ctors_aux () from ...boost/lib/libboost_wave-gcc46-mt-d-32-SOLARIS-X86-1_52.so.1.52.0 #15 0xfe88692a in _init () from ...boost/lib/libboost_wave-gcc46-mt-d-32-SOLARIS-X86-1_52.so.1.52.0 #16 0xfefce37e in call_init () from /usr/lib/ld.so.1 #17 0xfefce1cf in is_dep_init () from /usr/lib/ld.so.1 #18 0xfefdaa4b in elf_bndr () from /usr/lib/ld.so.1 #19 0xfefc2ab4 in elf_rtbndr () from /usr/lib/ld.so.1 #20 0xfee60688 in ?? () #21 0xfee0c8f6 in boost::exception_detail::get_static_exception_object<boost::exception_detail::bad_alloc_>() at ./boost/exception/detail/exception_ptr.hpp:119 #22 0xfee0c0d2 in __static_initialization_and_destruction_0(__initialize_p=1, __priority=65535) at ./boost/exception/detail/exception_ptr.hpp:138 #23 0xfee0c271 in _GLOBAL__sub_I_future.cpp () at libs/thread/src/future.cpp:60 = = static initization of boost.thread library = #24 0xfee0d98d in __do_global_ctors_aux () from ...boost/lib/libboost_thread-gcc46-mt-d-32-SOLARIS-X86-1_52.so.1.52.0 #25 0xfee0d9ba in _init () from ...boost/lib/libboost_thread-gcc46-mt-d-32-SOLARIS-X86-1_52.so.1.52.0 #26 0xfefce37e in call_init () from /usr/lib/ld.so.1 #27 0xfefce1cf in is_dep_init () from /usr/lib/ld.so.1 #28 0xfefdaa4b in elf_bndr () from /usr/lib/ld.so.1 #29 0xfefc2ab4 in elf_rtbndr () from /usr/lib/ld.so.1 #30 0xfdce0688 in ?? () = = First calll to boost::system::generic_category() = #31 0xfd81232a in boost::system::generic_category () at libs/system/src/error_code.cpp:425 #32 0xfd812386 in __static_initialization_and_destruction_0(__initialize_p=1, __priority=65535) at ./boost/system/error_code.hpp:214 #33 0xfd8123ed in _GLOBAL__sub_I_error_code.cpp () at libs/system/src/error_code.cpp:430 = = static initialization of boost.system = #34 0xfd8126ed in __do_global_ctors_aux () from ...boost/lib/libboost_system-gcc46-mt-d-32-SOLARIS-X86-1_52.so.1.52.0 #35 0xfd81271a in _init () from ...boost/lib/libboost_system-gcc46-mt-d-32-SOLARIS-X86-1_52.so.1.52.0 #36 0xfefce37e in call_init () from /usr/lib/ld.so.1 #37 0xfefcd7d5 in setup () from /usr/lib/ld.so.1 #38 0xfefdba3e in _setup () from /usr/lib/ld.so.1 #39 0xfefc299c in _rt_boot () from /usr/lib/ld.so.1 #40 0x08047540 in ?? () #41 0x08047670 in ?? () More thanks for reading all.

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