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

[TypeTraits] is_base_of behavior
by Ioannis Papadopoulos 03 Jul '09

03 Jul '09

Hi, I'm getting different behaviours using is_base_of on different compilers (tested with gcc, icc, xlc). #include <boost/type_traits.hpp> #include <boost/static_assert.hpp> struct A { }; struct B : public A { }; int main() { // Compile fine under all compilers BOOST_STATIC_ASSERT( (boost::is_base_of<A,A>::value) ); // all fail in xlC 10.1, work fine in gcc 4.3-4.4 and icc 11 BOOST_STATIC_ASSERT( (boost::is_base_of<A,const A>::value) ); BOOST_STATIC_ASSERT( (boost::is_base_of<A,volatile A>::value) ); BOOST_STATIC_ASSERT( (boost::is_base_of<A,const volatile A>::value) ); // Compile fine under all compilers BOOST_STATIC_ASSERT( (boost::is_base_of<A,B>::value) ); BOOST_STATIC_ASSERT( (boost::is_base_of<A,const B>::value) ); BOOST_STATIC_ASSERT( (boost::is_base_of<A,volatile B>::value) ); BOOST_STATIC_ASSERT( (boost::is_base_of<A,const volatile B>::value) ); return 0; } Thanks

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One common mutex and lock to rule them all
by Ryan McConnehey 03 Jul '09

03 Jul '09

Are there plans to provide a command mutex and lock? I know there are versions in both the thread and interprocess library. I'm sure each library developed their own as the library was being created. I've seen users ask about different mutexes and lock before and usually they are directed to either of these libraries. It would seem, from a user perspective, that a more central location for mutexes and lock would be helpful. Possibly in it's own header library. Is there a plan to do this in the future? Ryan

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[Filesystem] API questions
by Alan M. Carroll 02 Jul '09

02 Jul '09

I am trying to use Boost.Filesystem and have run in to some issues with the API which may be actual problems or a lack of understanding on my part. 1) What is the generic way to create current directory and parent directory relative paths, e.g. "." and ".."? Currently for current directory I use boost::filesystem::path(boost::filesystem::path::string_type(1,boost::filesystem::slash<boost::filesystem::path>::value)) which is a bit verbose. Parent directory relative path is the same with '2' instead of '1'. Further, it presumes that string_type has a constructor taking a repeat count and a character which may not be true in all cases. I would define these functionally as path instances which, if passed to current_path, would stay in the same directory or move to the parent directory respectively. Is this usage too file system specific to be included in the library? Is there a superior way to create such paths? 2) Why isn't there a path constructor / generator which takes a pair of path element iterators? E.g. like path make_path(path::iterator x, path::iterator y) { path zret; for ( ; x != y ; ++x ) zret /= *x; return zret; } 3) I tried to write my own templated make_path but I don't see how to either use the path class as the template parameter or compute the path class from its iterator. That is, I want to use path::iterator x,y; // set somehow path p = make_path(x,y); Implemetation 1: template < typename Path > Path make_path(Path::iterator x, Path::iterator y) { ... } This fails because Path can not be deduced from the use of Path::iterator instances. Implementation 2: template < typename PathIter> ??? make_path(PathIter x, PathIter y) {...} I don't see how to specify the return type given the type of an iterator. I think it would be reasonable to put this in the iterator class typedef boost::BOOST_FILE_SYSTEM_NAMESPACE::basic_path<String, Traits> path_type; which would solve my problem. I was able to make it work with VC9 by adding this to the iterator definition in path.hpp typedef path_type path_type; // import from enclosing scope for clients but I don't know how portable that is. 4) My actual goal is to write the function path between(path here, path there) which returns a path such that after current_path(here); current_path(between(here,there)); this returns true equivalent(current_path(), there); and where the returned path is as relative as possible. This is very handy for file generation to generate # include "../inc/thing.h" instead of # include "C:/Documents and Settings/amc/view/main/inc/thing.h" If there is already an easy way to do that, I would be happy to be so informed. Thanks.

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Support of Pretty print
by Mario Chacon 02 Jul '09

02 Jul '09

Hello: Is is possible that boost have gdb pretty prints??.. It's works great with std objects, it will be awesome if boost have it too!! Salu2... masch...

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problems using serialization/export.hpp
by Andrew Michael Levin 02 Jul '09

02 Jul '09

I am having problems compiling the following file called save_a.cc. #include "save_a.hh" #include <string> #include <fstream> #include <boost/archive/text_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> #include <boost/serialization/export.hpp> BOOST_IS_ABSTRACT(space::A) BOOST_CLASS_EXPORT(space::A) BOOST_CLASS_EXPORT(space::B) using namespace std; namespace space { void save(const A* _a, const string& _filename) { std::ofstream ofs(_filename.c_str()); OARCHIVE oa(ofs); oa & _a; ofs.close(); } } The errors that I get are as follows (I cut them off because they are a lot of them): [ 87%] Building CXX object src/shared/CMakeFiles/cryssmexlib.dir/test/save_a.o cd "/home/My Name/cryssmex/src/shared" && /usr/bin/c++.exe -Dcryssmexlib_EXPORTS -I/usr/include/boost-1_33_1 -I"/home/My Name/cryssmex/cryssmex/src/shared" -Wall -o CMakeFiles/cryssmexlib.dir/test/save_a.o -c "/home/My Name/cryssmex/cryssmex/src/shared/test/save_a.cc" /usr/include/boost-1_33_1/boost/serialization/export.hpp: In static member function `static void boost::archive::detail::guid_initializer<T>::export_register(const char*) [with T = space::A]': /usr/include/boost-1_33_1/boost/serialization/export.hpp:155: instantiated from `boost::archive::detail::guid_initializer<T>::guid_initializer(const char*) [with T = space::A]' /home/My Name/cryssmex/cryssmex/src/shared/test/save_a.cc:9: instantiated from here /usr/include/boost-1_33_1/boost/serialization/export.hpp:146: error: incomplete type `boost::serialization::extended_type_info_null<space::A>' used in nested name specifier /usr/include/boost-1_33_1/boost/serialization/export.hpp: In static member function `static void boost::archive::detail::guid_initializer<T>::export_register(const char*) [with T = space::B]': /usr/include/boost-1_33_1/boost/serialization/export.hpp:155: instantiated from `boost::archive::detail::guid_initializer<T>::guid_initializer(const char*) [with T = space::B]' /home/My Name/cryssmex/cryssmex/src/shared/test/save_a.cc:10: instantiated from here /usr/include/boost-1_33_1/boost/serialization/export.hpp:146: error: incomplete type `boost::serialization::extended_type_info_null<space::B>' used in nested name specifier /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp: In static member function `static void boost::archive::detail::save_pointer_type<Archive, TPtr>::save(Archive&, const T&, const boost::archive::detail::basic_pointer_oserializer*) [with T = space::A, Archive = boost::archive::text_oarchive, TPtr = const space::A*]': /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:467: instantiated from `static void boost::archive::detail::save_pointer_type<Archive, TPtr>::invoke(Archive&, TPtr) [with Archive = boost::archive::text_oarchive, TPtr = const space::A*]' /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:536: instantiated from `void boost::archive::save(Archive&, const T&) [with Archive = boost::archive::text_oarchive, T = const space::A*]' /usr/include/boost-1_33_1/boost/archive/basic_text_oarchive.hpp:78: instantiated from `void boost::archive::basic_text_oarchive<Archive>::save_override(T&, int) [with T = const space::A* const, Archive = boost::archive::text_oarchive]' /usr/include/boost-1_33_1/boost/archive/detail/interface_oarchive.hpp:78: instantiated from `Archive& boost::archive::detail::interface_oarchive<Archive>::operator<<(T&) [with T = const space::A* const, Archive = boost::archive::text_oarchive]' /usr/include/boost-1_33_1/boost/archive/detail/interface_oarchive.hpp:86: instantiated from `Archive& boost::archive::detail::interface_oarchive<Archive>::operator&(T&) [with T = const space::A*, Archive = boost::archive::text_oarchive]' /home/My Name/cryssmex/cryssmex/src/shared/test/save_a.cc:18: instantiated from here /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:438: error: invalid use of undefined type `struct boost::serialization::extended_type_info_null<space::A>' /usr/include/boost-1_33_1/boost/serialization/type_info_implementation.hpp:26: error: declaration of `struct boost::serialization::extended_type_info_null<space::A>' /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:439: error: invalid use of undefined type `struct boost::serialization::extended_type_info_null<space::A>' /usr/include/boost-1_33_1/boost/serialization/type_info_implementation.hpp:26: error: declaration of `struct boost::serialization::extended_type_info_null<space::A>' /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:439: error: `save' is not a member of `<declaration error>' /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp: In static member function `static const boost::archive::detail::basic_pointer_oserializer* boost::archive::detail::save_pointer_type<Archive, TPtr>::abstract<T>::register_type(Archive&) [with T = const space::A, Archive = boost::archive::text_oarchive, TPtr = const space::A*]': /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:360: instantiated from `static const boost::archive::detail::basic_pointer_oserializer* boost::archive::detail::save_pointer_type<Archive, TPtr>::register_type(Archive&, T&) [with T = const space::A, Archive = boost::archive::text_oarchive, TPtr = const space::A*]' /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:460: instantiated from `static void boost::archive::detail::save_pointer_type<Archive, TPtr>::invoke(Archive&, TPtr) [with Archive = boost::archive::text_oarchive, TPtr = const space::A*]' /usr/include/boost-1_33_1/boost/archive/detail/oserializer.hpp:536: instantiated from `void boost::archive::save(Archive&, const T&) [with Archive = boost::archive::text_oarchive, T = const space::A*]' /usr/include/boost-1_33_1/boost/archive/basic_text_oarchive.hpp:78: instantiated from `void boost::archive::basic_text_oarchive<Archive>::save_override(T&, int) [with T = const space::A* const, Archive = boost::archive::text_oarchive]' /usr/include/boost-1_33_1/boost/archive/detail/interface_oarchive.hpp:78: instantiated from `Archive& boost::archive::detail::interface_oarchive<Archive>::operator<<(T&) [with T = const space::A* const, Archive = boost::archive::text_oarchive]' /usr/include/boost-1_33_1/boost/archive/detail/interface_oarchive.hpp:86: instantiated from `Archive& boost::archive::detail::interface_oarchive<Archive>::operator&(T&) [with T = const space::A*, Archive = boost::archive::text_oarchive]' /home/My Name/cryssmex/cryssmex/src/shared/test/save_a.cc:18: instantiated from here ... ... Any idea what the problem is? Thanks.

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Confused about shared_mutex usage.
by Jason Cipriani 02 Jul '09

02 Jul '09

Hi all, I'm looking at the shared_mutex documentation here: http://www.boost.org/doc/libs/1_35_0/doc/html/thread/synchronization.html#t… But the documentation seems to be a little bit sparse and I'm having trouble figuring out how to use shared_mutex as a read/write lock. Just to make sure, lock_shared/unlock_shared is for the "readers", and lock/unlock is for the "writers"? If not, how do I lock/unlock it for reading, and how do I lock/unlock it for writing (exclusive lock)? Also I'm having trouble understanding what a "lock" is as opposed to a mutex. What is boost::shared_lock? Thanks! Jason

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Using mpl to instantiate template function
by Richard Hazlewood 02 Jul '09

02 Jul '09

Is there a type-only based way (e.g. with fold) of getting mpl to stamp out template functions for a collection of types? For example, this appears to work using mpl::for_each template <typename T> void Foo(); typedef mpl::vector<t1, t2, t3> Types; struct StampOut { template <typename T void operator()(const T *) const { Foo<T>(); } }; void dummy_() { mpl::for_each<Types>(Types, add_pointer<mpl::_1> >(StampOut()); } However, it requires the "dummy_" function to force instantiation. Is there an alternative trick?

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[interprocess] named_upgradable_mutex
by Moritz 02 Jul '09

02 Jul '09

Hi everybody, I have a question concerning the interprocess::updgradable::mutex. My scenario: I have a writer, which is manipulating an object in a interprocess::managed_shared_memory. And I have 'n' readers which are reading the object in the shared mem. If the writer is ready to write, it should get the possibility as fast as possible. So this is a variety of the classical readers/writers problem and I already found a good solution that fits my requirements. But this solution uses 3 mutexes and 1 counter so I am looking for a more efficient solution. The idea is that the writer locks the upgradable_mutex normally (calling lock()) and the readers lock it sharable (calling lock_sharable()). If the mutex is locked sharable and the writer tries to lock it normally, another attempt to lock it sharable has to wait until the writer succeeded in locking and unlocking the mutex. Is this correct proceeding? Thank you Moritz

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python context scope question
by Christopher Harvey 02 Jul '09

02 Jul '09

I'm running a bunch of python scripts from a directory, one after the other. I want to make sure that those scripts don't interfere with each other. My code looks like this: for(directory_iterator itr(filterDir);itr!=directory_iterator();++itr) { if(itr->path().extension()==".py") { try { object global = import("__main__").attr("__dict__"); object sys = import("sys"); sys.attr("path").attr("append")(str(filterDir)); exec_file(str(itr->path().string()), global, global); } catch(error_already_set const &) { cout<<"Python syntax/runtime error."<<endl; PyErr_Print(); } catch(...) { cout<<"Uknown error from script file: "<<itr->path()<<endl; } } } Basically what I want to know is this: For every iteration of the exterior for loop will any of the scripts that are executed be able to impact in any way another script that is executed? For example, I was thinking a script could remove that path that I want to add from the import search paths and break the next script that is run, since it wouldn't have that path. thanks.

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[Interprocess] [AIX 6.0] Abort and Segfault when calling destroy
by Thomas d'Erceville 01 Jul '09

01 Jul '09

Hello, Is there any support for boost on AIX 6.0? Because I got some trouble using boost::interprocess in this system. Actually, the rbtree_best_fit aborts (or Segfaults) when I try to destroy an object previsouly created by a construct. Here below a sample that aborts on AIX 6.0, compiled with boost 1.37: * managed_mapped_file mapfile(bi::create_only, address, size); Message * message = (mapfile.construct<Message>(bi::anonymous_instance))(); mapfile.destroy_ptr<Message>(message);* This abort message is : *Assertion failed :priv_is_allocated_block(block), file /..../boost/interprocess/mem_algo/rbtree_best_fit.hpp, line 1280* The full example is given by the linked file to this mail. I tried to replace the *rbtree_best_fit* by a *simple_seq_fit* but it doesn't change anything (except the abort message). Currently I can't use boost 1.38 or 1.39 because it can't compile it with xlc_r on AIX 6.0. So if someone has any option to solve this problem I take it! Best regards. Thomas d'Erceville

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