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[Date Time] time_period has not default constructor
by Pablo Madoery 30 Apr '14

30 Apr '14

I am using the library Date Time, in particular the object time_period. I was wondering why (if there is a good reason) this class has not a default constructor. the default constructor result usefull when using for example a map with the operator [] or when using serialization from Boost. ptime class has default constructor. If a time_period is formed by two ptime objects, why time_period has not its default constructor as well. Thanks

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allocating shared memory fails beyond 8 GB
by vipin sachdeva 30 Apr '14

30 Apr '14

Hi, I am using managed_xsi_shared_memory to allocate memory as below: boost::interprocess::managed_xsi_shared_memory shmem(boost::interprocess::create_only, key, atol(argv[2])); For some reason, I cannot allocate more than 8 GB of memory. Both sysctl and ipcs have limits higher than that set (output below). ------ Shared Memory Limits -------- max number of segments = 1874919423 max seg size (kbytes) = 9765624999999 max total shared memory (kbytes) = 39999999999999996 min seg size (bytes) = 1 kernel.shmmax = 9999999999999999 kernel.shmall = 9999999999999999 kernel.shmmni = 1874919423 vm.hugetlb_shm_group = 0 Is there any reason why this allocation should fail ?

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[typeindex v3.0] Peer review begins Mon 21st ends Wed 30th
by Niall Douglas 30 Apr '14

30 Apr '14

Dear Boost, A second round of community review begins for proposed Boost.TypeIndex on Mon 21st, lasting ten days. I should apologise as it's my fault for starting another peer review straight after Boost.Align ends, however I was busy as Google Summer of Code admin until today, and I will be preparing to talk at C++ Now straight after this review ends. I hope that this doesn't affect the community's willingness to contribute to the review. Reminder of the report from the last TypeIndex v2.1 review: https://groups.google.com/forum/#!topic/boost-list/TeiSdkRkUF0 Reminder of the original peer review announcement: http://boost.2283326.n4.nabble.com/TypeIndex-Peer-review-period-for-li brary-acceptance-begins-ending-Thurs-21st-Nov-td4654788.html Source code: https://github.com/apolukhin/type_index/zipball/master Github: https://github.com/apolukhin/type_index Documentation: http://apolukhin.github.com/type_index/index.html Changes in TypeIndex v3.0 since v2.1 (from my own review of it): 1. Documentation is hugely improved over v2.1, lots of side by side examples illustrating the differences and similarities. 2. You can now create your own custom type indices using an extensible framework. 3. boost::typeind::type_info now exports raw_name() and pretty_name() to maximise MSVC-GCC compatibility, and to solve point 1 but not point 2 in the v2.1 report. 4. The undefined behaviour trick used in v2.1 has been replaced with a cast via the placeholder type boost::typeind::detail::ctti_data which can be viewed in https://github.com/apolukhin/type_index/blob/master/include/boost/type _index/ctti_type_index.hpp. There is an explanation in the comments there about this technique's compatibility with the C++ standard. 5. TypeIndex now defines everything in the boost::typeind namespace instead of the boost namespace. So: 1. What is your evaluation of the design? 2. What is your evaluation of the implementation? 3. What is your evaluation of the documentation? 4. What is your evaluation of the potential usefulness of the library? 5. Did you try to use the library? With what compiler? Did you have any problems? 6. How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? 7. Are you knowledgeable about the problem domain? And finally, every review should answer this question: 8. Do you think the library should be accepted as a Boost library? Be sure to say this explicitly so that your other comments don't obscure your overall opinion. Thanks, Niall -- Currently unemployed and looking for work in Ireland. Work Portfolio: http://careers.stackoverflow.com/nialldouglas/

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update cycle
by Philipp Kraus 30 Apr '14

30 Apr '14

Hello, I try to compile Boost myself under OSX and the thread library runs into compiler errors. I have seen that the fix is inserted into the repo, so I would like to wait to a new Boost release. The last Boost version (1.55.0) was released on November 2013, so my question is in which cycles are new releases created (half a year)? Thanks Phil

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Boost::Interprocess - using variadic template args with managed_shared_memory::construct()
by james 28 Apr '14

28 Apr '14

Hi, I'm trying to write a wrapper over some of boost::interprocess and I want to have a function like this: template <typename T, typename... Args> T* Wrapper::createStruct(const std::string& name, Args&&... args) { return m_shm->construct<T>(name.c_str())(std::forward<Args>(args)...); } This fails to compile as it seems boost::interprocess uses its own varargs scheme when I try to create the following struct in the SHM through this wrapper function: struct Custom { Custom(int a, int b) : m_a(a), m_b(b) { } int a; int b; } int main() { ... Custom* c = shm->createStruct("Custom", 1, 2); } The error message: /usr/include/boost/interprocess/detail/named_proxy.hpp:79:7: error: no matching function for call to ‘test_sharedmemory::sharedmemory_custom::test_method()::Custom::Custom()’ { new((void*)mem)T(boost::forward<Args>(get<IdxPack>(args_))...); } ^ /usr/include/boost/interprocess/detail/named_proxy.hpp:79:7: note: candidates are: /home/james/dev/infinityplus/test/common/shm/sharedmemory/main.cpp:136:7: note: test_sharedmemory::sharedmemory_custom::test_method()::Custom::Custom(int, int) Custom(int one, int two) ^ /home/james/dev/infinityplus/test/common/shm/sharedmemory/main.cpp:136:7: note: candidate expects 2 arguments, 0 provided Is there any way I can get this to work? I'd rather my wrapper's interface used std only. boost 1.55 c++11 g++ 4.8.2 TIA, James

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Announcing the student program for Meeting C++ 2014
by Jens Weller 28 Apr '14

28 Apr '14

Hello C++ and Boost Community, today I have the honor to announce the student program for Meeting C++ 2014: > The Meeting C++ Student program will enable 50 students to attend Meeting C++ 2014 plus 3 exclusive workshops organized by think-cell one day before the conference on December 4th. So, for students this will be a 3 day conference! After the workshops you will be invited to the student dinner by think-cell. Further details at http://meetingcpp.com/index.php/newsreader/items/meeting-cpp-2014-the-stude… kind regards, Jens Weller

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[Coroutine 1.54] Compile error with bool return from coroutine-function
by Rob Desbois 27 Apr '14

27 Apr '14

(Caveat: I've been unable to find anything about this; hopefully haven't missed anything obvious.) (Apology: I'm aware Coroutine has a new interface as of 1.55; I haven't determined whether it is also affected.) Given the following code: #include <cassert> #include <boost/bind.hpp> #include <boost/coroutine/coroutine.hpp> using coro_t = boost::coroutines::coroutine< bool() >; void get_a_bool( coro_t::caller_type& yield ) { while (true) yield(true); } int main() { coro_t producer( boost::bind(&get_a_bool, _1) ); assert( producer ); } I get this error on compilation (g++ 4.8.2, Boost 1.54): rob{code 0} 839# clear && g++ boost-coroutine-bool-return.cpp -g -W -Wall --std=c++11 -L. -lboost_context -lboost_coroutine -o boost-coroutine-bool-return In file included from /usr/include/boost/coroutine/v1/detail/coroutine_base_resume.hpp:26:0, from /usr/include/boost/coroutine/v1/detail/coroutine_base.hpp:21, from /usr/include/boost/coroutine/v1/coroutine.hpp:30, from /usr/include/boost/coroutine/coroutine.hpp:13, from boost-coroutine-bool-return.cpp:11: /usr/include/boost/coroutine/detail/holder.hpp: In instantiation of ‘struct boost::coroutines::detail::holder<bool>’: /usr/include/boost/coroutine/v1/detail/coroutine_base_resume.hpp:103:28: required from ‘void boost::coroutines::detail::coroutine_base_resume<Signature, D, void, 1>::resume(boost::coroutines::detail::coroutine_base_resume<Signature, D, void, 1>::arg_type) [with Signature = void(bool); D = boost::coroutines::detail::coroutine_base<void(bool)>; boost::coroutines::detail::coroutine_base_resume<Signature, D, void, 1>::arg_type = bool]’ /usr/include/boost/coroutine/v1/detail/coroutine_op.hpp:268:9: required from ‘D& boost::coroutines::detail::coroutine_op<Signature, D, void, 1>::operator()(boost::coroutines::detail::coroutine_op<Signature, D, void, 1>::arg_type) [with Signature = void(bool); D = boost::coroutines::coroutine<void(bool), 1>; boost::coroutines::detail::coroutine_op<Signature, D, void, 1>::arg_type = bool]’ boost-coroutine-bool-return.cpp:29:13: required from here /usr/include/boost/coroutine/detail/holder.hpp:39:14: error: ‘boost::coroutines::detail::holder<Data>::holder(boost::coroutines::detail::coroutine_context*, bool) [with Data = bool]’ cannot be overloaded explicit holder( coroutine_context * ctx_, bool force_unwind_) : ^ /usr/include/boost/coroutine/detail/holder.hpp:35:14: error: with ‘boost::coroutines::detail::holder<Data>::holder(boost::coroutines::detail::coroutine_context*, Data) [with Data = bool]’ explicit holder( coroutine_context * ctx_, Data data_) : At a glance it looks like there's no way a coroutine-function could possibly return bool due to the overload collision. Is this right? Did I miss something completely obvious in the docs? It's easy enough to work around with a transparent bool wrapper, I just want to be sure I'm not being a muppet :-D TIA -- rob -- Rob Desbois http://theotherbranch.wordpress.com/

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Boost PropertyTree: read_json() followed by write_xml produces invalid XML
by Marcel Loose 27 Apr '14

27 Apr '14

Hi all, I was quite surprised and disappointed to find out that I was unable to convert a simple JSON file into XML, using the Boost PropertyTree. As input I used the example JSON file from the documentation (see example.json below). I wrote a small program (see example.cc below) that reads in this JSON file, writes it to disk as XML file, and finally tries to read back this XML file. This last operation fails with an exception (see output below); the XML file that is produced (see example.xml below) is invalid, because it contains empty tags (<>). Am I doing something wrong? Best regards, Marcel Loose. $ cat example.json { "menu": { "foo": true, "bar": "true", "value": 102.3E+06, "popup": [ {"value": "New", "onclick": "CreateNewDoc()"}, {"value": "Open", "onclick": "OpenDoc()"} ] } } $ cat example.cc #include <boost/property_tree/ptree.hpp> #include <boost/property_tree/json_parser.hpp> #include <boost/property_tree/xml_parser.hpp> #include <fstream> using namespace std; using namespace boost::property_tree; int main() { ptree pt; { read_json("example.json", pt); ofstream ofs("example.xml"); write_xml(ofs, pt, xml_writer_make_settings(' ', 2)); } { ifstream ifs("example.xml"); read_xml(ifs, pt); } return 0; } $ ./example terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::property_tree::xml_parser::xml_parser_error> >' what(): <unspecified file>(7): expected element name Aborted $ cat example.xml <?xml version="1.0" encoding="utf-8"?> <menu> <foo>true</foo> <bar>true</bar> <value>102.3E+06</value> <popup> <> <value>New</value> <onclick>CreateNewDoc()</onclick> </> <> <value>Open</value> <onclick>OpenDoc()</onclick> </> </popup> </menu>

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Library advice
by Mathew Benson 27 Apr '14

27 Apr '14

Is there a boost library that I can use to dynamically deserialize structures from untyped buffers? I need to write code that receives a buffer of data from another computer, with some data serialized with bitfield structs. Yes, I do understand the difficulty of doing this and that it would have been easier if the data was serialized properly before transmission. I have no control over the transmitted data, but I can get the data format defined accurately. I fully understand the numerous edge cases and pitfalls with doing this and don't take the task lightly. Therefore, I'm looking for libs and open source code to make it easier. The incoming data format can and frequently does change so I can't hard code the format, but the format is defined in an XML file. I wrote an internal database containing field type, offset, and bit lengths, and populated via the XML file. My XML file is auto generated to match the as built interface definition, bit for bit. I wrote code that deserializes most of the data, but I need to rewrite it as a general purpose function to work for all cases, including bitfield structs. For now, I can assume same CPU (little endian) and the same compiler (gcc). However, both source and destination CPUs and OS's might be 32 bit or 64 bit. In future versions, I would like to add support for endian conversion and differing compiler packing. Does boost have something that would help? Sent from my Packard Bell 386

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[Range] Extending the library for a base class and all its derived - enable_if
by Albert Yiamakis 26 Apr '14

26 Apr '14

Hello, I am looking to make a class, whose definition I cannot touch, model a Range concept. To that end I use method 2, http://www.boost.org/doc/libs/1_55_0/libs/range/doc/html/range/reference/ex… However, I am unable to specialize the relevant metafunctions (range_const_iterator, range_mutable_iterator, range_iterator) since they do not have an additional template parameter that would permit me to employ enable_if. I have found this impossible without touching either the class' definition or the metafunctions. Perhaps there is some other trick I am not aware of, in which case I would greatly appreciate hearing about it. If such a trick does not exist, then should these metafunctions feature an additional template parameter? Given that this is one of the methods to extend the library, it would make sense that one wishes to do so on conditions that enable_if can check. Albert

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