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docs on new build system?
by Neal Becker 07 Feb '12

07 Feb '12

I am testing 1_49_0_beta1. I see my usual build failed, saying 'warning: mismatched versions of Boost.Build engine and core'. Taking a wild guess, tried cd tools/build/v2 sh ./bootstrap.sh sudo ./b2 install --prefix=/usr/local I see I now have a new bjam, and something called 'b2'. Should I be reading some new docs on how to use this stuff? Are there some docs? My old build procedure: bjam -sHAVE_ICU=1 -sEXPAT_INCLUDE=/usr -sEXPAT_LIBPATH=/usr/lib64 -- layout=tagged threading=single,multi stage Seems to be proceeding normally (so far)

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[hash] regular behaviour of hash function for double values
by Kai Schroeder 07 Feb '12

07 Feb '12

Hi, the following code: double fStart = 31337; double fEnd = 65536; double fStep = fStart - fEnd; fStep /= 512; for (int i = 0; i < 512; i++) { std::cout << std::hex << boost::hash<double>()(fStart + i * fStep) << std::endl; } leads to the output of surprisingly regular hash values (see end of mail). This seems to occur mainly if a power of two number of points is sampled equidistantly within an interval. Especially since some hash table implementations (e.g. intel's threading building blocks) only use the last few bits to determine the bucket, this can lead to very bad caching behaviour for the rather common case of regularly sampled points (equidistant samplings of power of 2 are e.g. common in computer graphics and numerical algorithms). Are you aware of this? Would you consider it a bug? Best regards, Kai Schroeder Output of code using Boost 1.48 (similar behaviour can be observed for other start and end values and other power of 2 step counts): ff9f20000000000f e5042f900000000f 52f13f200000000f 297ac8b00000000f 48721e400000000f 2f9b8dd00000000f 3df0b1600000000f d19cf2f00000000f 9201c800000000f 9409aa100000000f 7cb3fba00000000f d7a42b300000000f b15982c00000000f 5f7900500000000f e0ba85e00000000f 255ee5700000000f cec119000000000f 955bd6900000000f 6a58f4200000000f 843a37b00000000f 590797400000000f 7e8db4d00000000f 1721b6600000000f 37acf9f00000000f df5f65800000000f 88b1a5100000000f 494a0a00000000f bb1082300000000f 1ea62bc00000000f ...

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unordered_map 32bit VS 64bit
by Avikam Bara-nes 07 Feb '12

07 Feb '12

Hi, I'm porting a project from Linux 32bit to Linux 64bit. While doing so I notice that I have a dramatic performance degradation with unordered_map. My platform is Ubuntu 10.4.3 64bit running on Intel Xeon X3220 but, I tested similar program on WindowsXP SP2 64bit which running on Intel i5 and I get the same degradation. My boost version is 1_46_1. I use the following program in order to test unordered_map - Hop I didn't make any copy mistakes :-). #include <stdio.h> #include <sys/time.h> #include <boost/unordered_map.hpp> int main(int argc, char *argv[]) { struct timeval tv_before, tv_after; boost::unordered_map<boost::int_32_t, boost::int32_t> boost_map; boost_map[1] = 2; boost_map[3] = 4; gettimeofday(&tv_before, NULL); for(int i = ; i < 100000; i++) boost_map.find(1); gettimeofday(&tv_after, NULL); printf("Boost time is %f \n", (double)(((tv_after.tv_sec - tv_before.tv_sec) * 1000000 + (double)(tv_after.tv_usec - tv_before.tv_usec)) / 100000)); return 0; } I use the following compile commands: 64bit - g++ -O3 perf_test -o perf_test_64bit 32bit - g++ -m32 -O3 perf_test -o perf_test_32bit When I run the 32bit program I get 0.5 sec When I run the 64bit program I get 1.54 sec Any ideas ???

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[MPI]: All tests failing -- branch and trunk
by Steve M. Robbins 07 Feb '12

07 Feb '12

Hi, I have been running a daily test of the Boost release branch for a long time. It normally takes an hour or so. However, two days ago (rev 76868), the build time shot up to over 9 hours. The same thing happened for testing the Boost trunk branch. Others on the boost-test list have experienced the same and Jurgen Hunold pointed out that all the MPI tests are failing. According to http://www.boost.org/development/tests/trunk/developer/mpi.html this is true for about half the tester machines. Should probably be fixed before 1.49 is released! -Steve

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[functional] adding overload
by Lorenzo Caminiti 06 Feb '12

06 Feb '12

Hello all, During Boost.Local review, it was proposed to move the overload template out of Local and in Boost.Functional. What would the best name for it? 1) boost::overload_function (my preference) 2) boost::overloaded_function 3) boost::function_overload 4) boost::functional::overload (Boost.Functional seems to use boost:: directly and not boost::functional-- to mimic C++11 <functional>). For example: void print_text(char const* text) { std::cout << text << std::endl; } void print_add(int x, int y = 10) { std::cout << (x + y) << std::endl; } boost::function<void (int, int)> f = print_add; boost::overload_function< void (char const*) , void (int, int) , void (int) > print(print_text, f, print_add); print("abc"); // abc print(1, 2); // 3 print(1); // 11 Docs: https://svn.boost.org/svn/boost/sandbox/local/libs/local/doc/html/boost/loc… Thanks. --Lorenzo

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[filesystem] windows/posix inconsistencies.
by Thorsten Ottosen 06 Feb '12

06 Feb '12

Hi Beman, I noticed the following in v3 whie hunting down a bug in my unit test: # ifdef BOOST_WINDOWS_API const std::string string() const { return string(codecvt()); } const std::string string(const codecvt_type& cvt) const; // string_type is std::wstring, so there is no conversion const std::wstring& wstring() const { return m_pathname; } const std::wstring& wstring(const codecvt_type&) const { return m_pathname; } # else // BOOST_POSIX_API // string_type is std::string, so there is no conversion const std::string& string() const { return m_pathname; } const std::string& string(const codecvt_type&) const; const std::wstring wstring() const { return wstring(codecvt()); } const std::wstring wstring(const codecvt_type& cvt) const # endif I can understand, that it is more efficient to return a reference when a referenec can be formed. However, consider const std::string& ext = iter->path().extension().string(); This is fine on windows, as a temporary is returned, and its lifetime is extended; on linux, extension() returns a temp path object, from where we get a reference. I'm not a 100% sure, but I think the C++ standard does not guarantee that this path object be kept alive. The net efffect is a crash on linux. I'm not sure its a great idea to have different reference-ness on the return types here. It could lead to other subtle differences. kind regards -Thorsten

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[mpl] Nested Scopes w/Placeholders
by Kitten, Nicholas 06 Feb '12

06 Feb '12

I've recently been doing a lot mpl::folding (in boost 1.47), and I was disappointed when I realized that a nested fold wouldn't work with a lambda expression passed to the inner call, as in this example which extracts elements of sequences: using namespace mpl; using namespace mpl::placeholders; typedef vector< vector<char>, vector<int> > vec_of_vecs; typedef vector< char, int > expected_result; typedef fold< vec_of_vecs, vector<>, fold< _2, _1, *push_back< _1, _2 >* // wrong - refers to outer arguments > >::type result; BOOST_MPL_ASSERT(( equal<result, expected_result> )); After looking around for a solution I came across an old thread<http://lists.boost.org/boost-users/2004/12/9269.php> on the same subject, where it was suggested using mpl::protect might work. Indeed, the following modification does what I want, without any changes to the library: typedef fold< vec_of_vecs, vector<>, fold< _2, _1, *protect< lambda< push_back< _1, _2 > >::type >* // correct > >::type result; Of course, this is a little on the verbose side. In the old thread, Daniel Wallin suggested suggested changing the definition of lambda to yield syntax more in line with the runtime version of boost::bind, but that would apparently break other code. What about instead adding a specialization to protect for placeholder expressions? Indeed, the source in protect.hpp seems to indicate such a thing might've been in the works at one point, but I didn't see any more references to it: template< typename BOOST_MPL_AUX_NA_PARAM(T) * , int not_le_ = 0 // not lambda expression?* > struct protect : T { ... typedef protect type; }; What about changing it to something like this? template< typename BOOST_MPL_AUX_NA_PARAM(T) * , typename not_le_ = typename is_lambda_expression< T >::type* > struct protect : T { ... typedef protect type; }; *template< typename T >* *struct protect< T, mpl::true_ > : lambda<T>* *{* *...* *typedef protect type;* *};* Doing so would remove the inner lambda<...>::type expression, yielding the expected syntax. Could that be done without messing up everything else? Thanks, *Nick Kitten* Software Engineer Center for Video Understanding Excellence ObjectVideo, Inc.

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[gsoc] Summer of Code 2012
by Andrew Sutton 05 Feb '12

05 Feb '12

Has it been a year already? Google has just announced the 2012 Summer of Code program, and we'd like to participate again. I think last year was particularly successful. We reviewed and accepted two new libraries and moved several more into a state where they can be reviewed. This year should be interesting. We have a new C++ programming language, several libraries in the standard, and we want more. Many, many more. If you didn't get a chance to watch Herb Sutter's keynote talk at GoingNative 2012, you should. It will be available on-demand from this site some time in the next few days. http://channel9.msdn.com/Events/GoingNative/GoingNative-2012 [Spoiler alert] Herb wants libraries -- and not just tools for programmers. C++ wants UI libraries, graphics, database connectivity, cryptography, XML, network protocols, SMS support, back office support, etc. I would love to see some of these libraries developed through Boost. In C++11. Bjarne Stroustrup said he hadn't seen this much energy around C++ in a decade. People are excited to be writing C++11 -- and they're younger people for the first time in a long time. We should be capitalizing on this. If you have library ideas, please email me here: andrew.n.sutton -at- gmail.com. I will collect these and put them on the idea page. Some comments for mentors: I'm not concerned with summer-long time constraints this year. I'd really like to establish long-term relationships with our students. I'm not strictly concerned with backwards compatibility support. I think we should be encouraging students (and people in general) to write in C++. Hiding new language features behind compatibility macros isn't exciting. It might be fine for when time comes for releases, but let's not require students to build release-ready software. This year, I'd like to see proposals for *new* libraries to be written in C++11. Andrew

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[bgl] Maximum Adjacency Search
by Fernando Vilas 04 Feb '12

04 Feb '12

Hi, Well, it took me longer than "a few days" to make time to clean up the code, but here is a patch against today's SVN-trunk. It will probably need more cleanup before it is ready, but it should be at a point where public review will help. -- Thanks, Fernando Vilas fvilas(a)iname.com

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1.49.0 Beta 1 Release Candidate
by Steve M. Robbins 04 Feb '12

04 Feb '12

Hi, I'm starting a build (using the Debian package configuration) and noticed several known bugs still present: These two bugs are patched on the trunk but not release. Can these be moved over, please? https://svn.boost.org/trac/boost/ticket/4657 https://svn.boost.org/trac/boost/ticket/6338 This issue has a simple patch that works around the problem for gcc versions prior to 4.6.3: https://svn.boost.org/trac/boost/ticket/5538 This issue has a patch that works (is used in Debian), though a jam expert could likely find a better fix: https://svn.boost.org/trac/boost/ticket/6286 Regards, -Steve (Boost maintainer for Debian)

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