September 2010 - Boost - lists.boost.org

aligned_storage in unions
by dherring＠ll.mit.edu 24 Sep '10

24 Sep '10

Hi, While C++0x promises to change things (see draft spec section 9.5), C++ currently does not allow unions to contain members having a nontrivial constructor, operator=, or destructor. This excludes std::string, std::complex, structures containing either, etc. The "standard" workaround is to allocate your own memory and use manual type casting. Boost::aligned_storage can be used to maintain proper alignment, but it cannot be placed inside a union due to the default ctor, dtor, and noncopyable functions. Thus I am forced to use part of boost::detail. Here is a simple example. #include <boost/type_traits/aligned_storage.hpp> // define a union-safe wrapper template <class T> struct UnWrap { boost::detail::aligned_storage::aligned_storage_imp< sizeof(T), boost::alignment_of<T>::value> space; T * get() const { return static_cast<T *>(space.address()); } T * operator->() const { return get(); } T & operator*() const { return *get(); } }; union U { UnWrap<std::string> s; int x; }; U u; new (u.s.get()) std::string; *u.s="hi"; Questions: - Is there a better way to do this? - Am I doing something blatantly wrong? - Could aligned_storage_impl be exposed for such uses? (AIUI, the detail namespace contains unsupported internals.) Thanks, Daniel

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[ratio] 0.2 Review version uploaded
by vicente.botet 24 Sep '10

24 Sep '10

Hi, I have uploaded the version of the Boost Ratio library to be review. What is Boost.Ratio? =============== Boost.Ratio is a portable implementation of the C++0x Standard Library's compile-time rational arithmetic working on C++03 and C++0x compilers. Boost.Ratio provides: * A class template, ratio, for specifying compile time rational constants such as 1/3 of a nanosecond or the number of inches per meter. ratio represents a compile time ratio of compile time constants with support for compile time arithmetic with overflow and division by zero protection * A textual representation of boost::ratio<N, D> in the form of a std::basic_string. Other types such as boost::duration will use these strings to aid in their I/O. This library is header-only and is designed to be generic and useful in a lot of areas of C++ programming, in particular it is absolutely needed to Boost.Chrono and Boost.Stopwatches. Boost.Units contain a similar class: static_rational. You can get more complete information from http://svn.boost.org/trac/boost/wiki/LibrariesUnderConstruction#Boost.Ratio Best regards, _____________________ Vicente Juan Botet Escribá http://viboes.blogspot.com/

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Re: [boost] Is there any interest in a smart pointer facade class?
by Krzysztof Czainski 23 Sep '10

23 Sep '10

> > Stefan Strasser <strasser(a)uni-bremen.de>: > >> Recently I wrote two smart pointer classes, and felt the need for such a >>>> class. I would like to write such a class, and if everything goes well, >>>> perhaps add it to the Boost library. >>>> >>> >>> It is supposed to be something like a more powerful intrusive_ptr? >>> Can you give a usage example? >>> >> >> I think the general idea is that this would be closer to a policy-based >> smart pointer. >> >> > I think it`s neither, but a CRTP class implementing the "pointer concept": > > struct my_ptr > : smart_ptr_facade<my_ptr,...>{ > void set(T *rhs){ ptr=rhs; } > T *get() const{ return ptr; } > T *ptr; > }; > > => my_ptr has ptr semantics, including operator->, operator=, ... > > iterator_facade simplifies implementing iterators a lot, so could this > class for pointers, and other facades, e.g. a vector_facade that implements > the std::vector interface in terms of 3 or 4 user-supplied functions. > Yes, this is what I have in mind. In a simplified case, smart_ptr_facade would require from my_ptr to provide a T* get() const;, and smart_ptr_facade would provide operator*, operator->, operator==, operator< (in order to be able to keep my_ptr in std::set).

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[serialization] incompatible archives from 1.43 to 1.44
by Löw, Tobias (Evonik Energy Services GmbH) 23 Sep '10

23 Sep '10

Hi, I'm trying to read a binary archive with version 1.44 that was written with version 1.43. When loading I'm getting an exception in basic_binary_iarchive.ipp line 91 as the read library-version is higher than the boost-archive-version. The reason for that is that in line 80 * this->This() >> input_library_version; now two bytes are read whereas in prior boost-versions only one byte was read. There seems to be missing a load_override-function for library_version_type. Tobias

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Is there any interest in a smart pointer facade class?
by Krzysztof Czainski 22 Sep '10

22 Sep '10

Is there any interest in a smart pointer facade class? I have in mind a class, that works similarily to boost::iterator_facade for developers of smart pointers instead of iterators. template < class Derived, class Pointee > class smart_ptr_facade; Recently I wrote two smart pointer classes, and felt the need for such a class. I would like to write such a class, and if everything goes well, perhaps add it to the Boost library. Regards Krzysztof Czainski

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[serialization] feedback on a possible port of the XML archive grammar to Qi
by Bryce Lelbach aka wash 22 Sep '10

22 Sep '10

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I've recently started working on porting Boost.Serialization's XML parser from Spirit Classic to Spirit Qi (I've got some free time on my hands, and I heard that there was some interest in this task). Before I start putting more time into this, I'd love to get some feedback/suggestions and make sure someone else isn't already working on this. My understanding is that porting the parser from Spirit Classic to Spirit Qi will not only speed up XML serialization, but would also increase portability (on some compilers, Serialization only works with Spirit 1.6, which is not shipped with the latest Boost release). My current plan is to rewrite the grammar in Qi, and modify the existing XML archive classes to use the new parser without changing the interface or the outputted XML. - Bryce Lelbach -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkx9e9oACgkQO/fqqIuE2t4IRwCdGOUqHtLhWeVIK3ruTipf4jHu +j8AoIP7CUssPlkBpLTWLHYRcPls0/ZJ =ki/H -----END PGP SIGNATURE-----

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[Regex] Building Boost.Regex with ICU
by Artyom 22 Sep '10

22 Sep '10

Hello, I'm trying to build some basic Boost.Locale Jam file on base of Boost.Regex one, however... I can't even build Boost.Regex with ICU at all. Version 1.43 ------------ Debian, ICU 3.8 installed in regular place /usr/lib/libicu*.so Build: bjam -d+2 -sHAVE_ICU=1 stage Shows that the build is done with ICU (i.e. -DBOOST_HAS_ICU=1 in command line of gcc) However when afterward I check ldd stage/lib/libboost_regex.so It shows no evidence of linking with ICU. Version 1.44 ------------ Build: bjam -d+2 -sHAVE_ICU=1 stage Shows that the build is done without ICU! i.e. -DBOOST_HAS_ICU=1 in command line of gcc is NOT defined. And of course ldd shows the same Even if I specify bjam -d+2 -sHAVE_ICU=1 -sICU_PATH=/usr stage Or try to use ICU4.4 installed on other location bjam -d+2 -sHAVE_ICU=1 -sICU_PATH=/opt/icu44 stage Same result. I don't understand how can I actually get the library (especially recent) built with ICU. Artyom

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[preprocessor] macro #definition order
by Lorenzo Caminiti 21 Sep '10

21 Sep '10

Hello all, I have a curiosity about the preprocessor: In the following example, is there any difference if `CONCAT()` is #defined before or after `CONCAT_D()`? Example 1: #define CONCAT(a, b) CONCAT_D(a, b) #define CONCAT_D(a, b) a ## b Example 2: #define CONCAT_D(a, b) a ## b #define CONCAT(a, b) CONCAT_D(a, b) In other words, are example 1 and 2 completely equivalent? Or, is there is a functional difference (proper expansion order, portability, etc)? Or, is there a performance difference (number of macro expansions, preprocessing time, etc)? I am asking because I would like to understand *in general* if the order in which I #define my macros when I program the preprocessor using Boost.Preprocessor might make a difference either functionally or for performance. Thank you very much. -- Lorenzo

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[config] additions for gcc 4.0.1 and IBM V11.1.0.0 due to MSM compile errors
by Christophe Henry 21 Sep '10

21 Sep '10

Hi, I'm trying to see how far I can bring more compilers to compile MSM and I noticed that these 2 compilers might have a chance to work: - On gcc 4.0.1, most regression tests (for example: http://www.boost.org/development/tests/trunk/developer/output/Sandia-darwin…) fail because in msm/back/state_machine.hpp, the nested struct add_state cannot access the private function set_containing_sm. IIUC this should be BOOST_NO_NESTED_FRIENDSHIP. Correct? If yes, could we add this macro for gcc 4.0.1 (unfortunately, no idea about 4.0.1 - 4.2 but I suppose this will concern all 4.0.x)? - Again on the regression tests, the IBM compiler shows the same problem and furthermore does not accept that the struct: template <class Fsm,class Stt, class Event, class Compile> friend struct dispatch_table can have access to a private method of the befriended class. Again, IIUC, this seems to me to be BOOST_NO_MEMBER_TEMPLATE_FRIENDS. I don't find a file for this compiler in config/compiler. Am I missing something? Frankly, I'm slightly wary of changing myself the config files so I'd really appreciate some help here. Thanks, Christophe

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Re: [boost] [filesystem] Link errors on Linux/MacOS with v3
by cheesy4poofs 21 Sep '10

21 Sep '10

>>... ?When I attempt to build boost >> on Mac/Linux with -DBOOST_FILESYSTEM_VERSION=3 ... > >Whoa! That may be the problem. > >When you compile your program it needs -DBOOST_FILESYSTEM_VERSION=3, >but when you compile that boost libraries, you should not define >anything special. > >What does the bjam command you are using for building the boost >libraries look like? > >--Beman I have discovered the issue. My apologies for wasting your time. My coworker built boost 1.44 (on Mac/Linux) with the CMake version of boost builds and the CMake version has a bug in that they don't include the v3 source in the final libraries. Once I modified CMakeLists.txt to add all the v3 source files for filesystem, everything is linking fine. BTW, I built boost on windows with bjam, which is why I never encountered the problem. Thanks again for the help. --Scott

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