- Boost - lists.boost.org

[python] Making a Python tuple from a Fusion sequence
by Bruno Lalande 27 Feb '09

27 Feb '09

Hello, I have written a little function that converts any Boost.Fusion sequence into a Python tuple (boost::python::tuple). If a sub-sequence is nested in the sequence, the result will also be a nested tuple (for instance, boost::make_tuple(0, std::make_pair(1, 2), 3) will give (0, (1, 2), 3) in Python). The source code is attached to this mail. The principle is that any sequence previously adapted to Boost.Fusion will become a tuple in Python. So, by including the right boost/fusion/adapted/xxx header, one can convert a pair, a tuple, a boost::array, and obviously any of the sequences provided by Boost.Fusion. For example: #include <boost/python.hpp> #include <boost/fusion/adapted/std_pair.hpp> #include <boost/fusion/adapted/boost_tuple.hpp> #include <boost/fusion/container/generation/make_vector.hpp> #include "make_tuple_from_fusion_sequence.hpp" using namespace boost::python; tuple from_sequence() { return make_tuple_from_fusion( boost::fusion::make_vector( 1, std::make_pair("first", "second"), 2, boost::make_tuple('a', 'b', 'c'), 3 ) ); } BOOST_PYTHON_MODULE(mymodule) { def("from_sequence", &from_sequence); } In Python we get: >>> import mymodule >>> mymodule.from_sequence() (1, ('first', 'second'), 2, ('a', 'b', 'c'), 3) Is there any interest in adding this function into Boost.Python? If yes, I can write the doc and tests, clean the source and maybe improve the implementation (for example, I feel that I could avoid the use of m_iteration with a better use of Boost.Fusion...). Regards Bruno

5 9

another approach to memory management that solves the referential cycles problem
by Achilleas Margaritis 27 Feb '09

27 Feb '09

Dear boost members, I have placed in the boost Vault, under the section "memory", the file 'mm.zip' which contains: 1) a file "readme.txt" with a little documentation. 2) a file 'main.cpp' which contains a reference implementation and test. This (I wouldn't not call it new, but certainly interesting) approach to memory management solves the problem of cycles and it can also provide a sort of garbage collection, without the issues of other approaches (explained in the readme). Suggestions, comments, ideas, etc are welcomed.

3 10

Re: [boost] [geometry] area, length, centroid, behaviour
by Mika Heiskanen 27 Feb '09

27 Feb '09

I wrote: > However, I'd hate to have to produce a certain winding rule for the > exterior and the holes in order to use the same data for more > complicated GIS calculations such as logical operations and buffering. > IMHO it should be just as easy as choosing to use the even-odd filling > rule instead of the winding rule. To which Barend Gehrels replied: > It cannot be called from the algorithms themselves: to > verify the winding rule the area has to be calculated beforehand. This > will drastically decrease performance. Certainly area calculation is significantly faster than logical operations and buffering. > The solution might be a traits class telling the winding rule the > polygon type has. Agreed. [Sorry about the unorthodox quoting, I rebuilt the reply by googling] --> Mika Heiskanen

1 0

Interest check: factory patterns
by Tor Brede Vekterli 27 Feb '09

27 Feb '09

Hi all I've been working on a "Modern C++ Design"-inspired factory/abstract factory pattern implementation for a while now, and was wondering if there was any interest in having it as a Boost library at some point? If my understanding of the existing Boost.Functional/Factory is correct, then this should not really clash with its area of operation. Factory features - Configurable identifier, mapping, error policy types - Function storage type can be overridden by the user on a per-factory basis Abstract factory features: - Auto-generation of class hierarchies (a-la Loki)--allows passing as individual factory fields - Passing of construction-arguments to the concrete type "creators" (operator new by default, but extensible) - Prototypes - Easy (re-)binding of constructor arguments - Boost.Functions if none of the above are appropriate or flexible enough - Mixing and matching creators for concrete factories. i.e., allows to use a prototype for one concrete type, Boost.Function for another, operator new for the third and so on - Easily specify if the created object should be returned as a raw pointer or a smart pointer (any type with a nested element_type is automatically recognized) - Almost everything is policy-specifyable Somewhat contrived example: typedef abstract_factory< // Want object created with no args, returned as raw pointer abstract_foo* // Want object created with std::string const ref, float by value args; returned as auto_ptr , std::auto_ptr<abstract_bar>(const std::string&, float) > abstract_factory_t; concrete_factory< // Concrete factory for abstract_factory_t abstract_factory_t // Concrete creator for abstract_foo; prototype , prototype<> // Concrete creator for abstract_bar; operator new creator (default when it's a regular type) , bar_impl > cf; // Set prototype for abstract_foo (takes ownership of raw pointers) cf.prototype<abstract_foo>(new fancy_foo_impl); const abstract_factory_t& af = cf; // By default invoke clone() on the stored prototype abstract_foo* foobj = af.create<abstract_foo>(); // Forward args to creator, in this case operator new --> constructor of bar_impl std::auto_ptr<abstract_bar> barobj = af.create<abstract_bar>("hello boost", 1234.5f); Preliminary documentation and download link can be found here: http://arcticinteractive.com/static/boost/libs/factory/doc/html/index.html I've yet to request any vault/sandbox access, because I first would really like to get some input on what people who are far more knowledgeable and experienced in C++ and software design than myself think of it :). Critique, comments, suggestions etc. are very welcome on all aspects of the library (code, design, documentation,...) Regards, Tor Brede Vekterli

1 0

Sandbox structure in subversion (was Re: [move] Library uploaded to sandbox)
by Daniel James 27 Feb '09

27 Feb '09

2009/2/17 Ion Gaztañaga <igaztanaga(a)gmail.com>: > > http://svn.boost.org/svn/boost/sandbox/libs/move_semantics/index.html [snip] > > For those that don't like svn sandbox (I'm one of them) I've also put the > code and the documentation here: Most people nowadays are putting their libraries into subdirectories of sandbox, instead of mixing it up with the stuff that's already there. It's much easier to check out and browse online. For example, there's chrono at: https://svn.boost.org/svn/boost/sandbox/chrono https://svn.boost.org/trac/boost/browser/sandbox/chrono It is messy having this in the middle of the old sandbox layout. We could separate out the two although doing this without disrupting development would be tricky. Maybe we could create a new space in subversion and let people migrate to it if they wish. We could use a more traditional subversion layout, perhaps something like: /svn/boost/projects/chrono/trunk /svn/boost/projects/chrono/branches /svn/boost/projects/move_semantics/trunk /svn/boost/projects/move_semantics/branches Daniel

6 10

[iostreams] detecting io errors
by Johan Grafstrom 27 Feb '09

27 Feb '09

Hello, I use boost:iostreams for reading and writing a binary data format. There is currently no use of filters, but the reason for using boost was to try using compression by adding a filter. I have run into some problems/questions regarding the boost:iostreams::stream class though, and was hoping that someone here might give me a hint. The files I save is project files, and the users use a versioning system to lock the files while editing. Occasionally they forget to lock and would get an error when trying to save, since the files in write protected unless locked. My first (and worst) problem was that i did not get any error at all when the write failed, I found out that this was my own fault since I used: bio::stream<bio::file_sink> outs(tstFileName, std::ios_base::out); // ... write etc... if (outs.is_open()) // error ... instead of if (outs->is_open()) // ^^ '->', not '.' must be used here // error ... but it seem like an easy pitfall for newbies like me. A different method name or at least a warning in the documentation maybe? The second problem is that I cannot find any way to get information on the nature of the write error. E g is it an access permission problem or a hardware error? The third problem is that seem to be no way to detect an error when closing the file. I have attached a short c-file to illustrate what I would want to know. I pause and remove the USB-stick with the open file before closing. c-runtime streams will give me error on close, but I cant get the same information out of boost::iostreams. Any help, directions or opinions would be appreciated. Best regards, Johan Grafström /* -*- mode: C++; coding: utf-8-dos; -*- */ /* ========================================================================== * boost_test2.cpp * * Problems: * * * Boost only reports false for outs->is_open() after error but gives no * details (write failure, invalid handle, access violation) * * * An error on file close cannot be detected * * * The worst problem was my own: * using outs.is_open() (always returns true) * instead of outs->is_open() returns false after error * * ========================================================================== */ #include <stdio.h> #include <conio.h> #include <boost/iostreams/device/file.hpp> #include <boost/iostreams/stream.hpp> void boostWriteTestFile(); void streamsWriteTestFile(); void userInteract(); namespace bio = boost::iostreams; char tstFileName[] = "write_test.txt"; int main(int argc, char *argv[]) { // DebugBreak(); if (argc == 2 && strcmp(argv[1],"streams") == 0) { printf("Write using c-runtime stream i/o\n"); streamsWriteTestFile(); } else { printf("Write using boost:iostreams\n"); boostWriteTestFile(); } return 0; } void boostWriteTestFile() { char streamText[] = "Written by boost iostreams api\n"; int msgSize = strlen(streamText); // write using boost bio::stream<bio::file_sink> outs(tstFileName, std::ios_base::out | std::ios_base::binary); int bytesWritten = outs->write(streamText, msgSize); if (bytesWritten != msgSize) printf("Error boost writing\n"); if (!outs->is_open()) printf("Error boost file closed\n"); userInteract(); // Problem: how to get error status from outs.close() ?? // returns void // in boost/iostreams/device/file.hpp:175 // template<typename Ch> // void basic_file<Ch>::close() { pimpl_->file_.close(); } // returns void thus ignoring the return value from // basic_filebuf.close() in c++ runtime <fstream> outs.close(); } void streamsWriteTestFile() { char streamText[] = "Written by c-runtume streams api\n"; int msgSize = strlen(streamText); // write using c-runtime streams FILE *fh = fopen(tstFileName, "w"); if (fh == NULL) { perror("on fopen()"); return; } size_t countWritten = fwrite( streamText, // const void *buffer, 1, // size_t size, msgSize, // size_t count, fh // FILE *stream ); if (countWritten != msgSize) { perror("On fwrite()"); return; } userInteract(); int status = fclose(fh); if (status == 0) { // ok } else { // status == EOF perror("on fclose()"); return; } } void userInteract() { printf("Please remove the file %s, in some apropriate manner e g \n" "remove the floppy or usb-drive, delete with Unlocker or equivalent.\n" "Then press any key to continue.\n", tstFileName); _getch(); }

1 0

[c++0x][trunk testing] regression tests broken
by David Deakins 27 Feb '09

27 Feb '09

Looking at the output from our regression test system, it appears that the recent cpp0x changes have broken regression testing on the trunk. From a cursory review, it looks like some of the .cpp test files now mentioned in libs/config/test/all/Jamfile.v2 did not get merged over from branches/cpp0x. I noticed that the 'no_char16_t_pass.cpp' and 'no_char16_t_fail.cpp' files are missing, along with the char32 tests, the decltype tests, the extern template tests, the long long tests, and possibly more. Beman, do you have time to take a look at this and see which additional files need to be merged over? If not, I could probably take a look but not until tomorrow. And if this has already been noticed and mentioned, my apologies for the redundant post. Thanks, -Dave Deakins

1 0

Formal Review: Boost.RangeEx
by Thorsten Ottosen 26 Feb '09

26 Feb '09

Dear Developers and Users, It's my pleasure to announce that the review of Neil Groves' RangeEx library starts today and lasts until March 3, 2009. What is it? +++++++++++ The library provide two very useful extensions to the range library 1. Range-based algorithms. E.g. boost::sort( rng ); which is a convenient wrapper of instead of std::sort( boost::begin(rng), boost::end(rng) ); But the new interface also allows for more expressive code because (on the fly) composition of algorithms suddenly is possible. 2. Range adaptors. E.g. std::vector<int> vec = ...; boost::copy( vec | boost::adaptors::reversed, std::ostream_iterator<int>( std::cout ) ); where the expression "vec | boost::adaptors::reversed" wraps the iterators of the range on the left in reverse iterators. The library provides a wide range (no pun intended) of Range adaptors, and they are a powerful way to create ranges on the fly and pass them to algorithms. Getting the library +++++++++++++++++++ The library may be downloaded from http://www.cs.aau.dk/~nesotto/boost/range_ex.zip or from the Boost vault under "Algorithms". The docs may be browsed online here http://www.cs.aau.dk/~nesotto/boost/libs/range/ Please note that the documentation is integrated with the current Range ilbrary. Therefore the relevant sections for the review is http://www.cs.aau.dk/~nesotto/boost/libs/range/doc/adaptors.html and http://www.cs.aau.dk/~nesotto/boost/libs/range/doc/algorithms.html The code may be browsed here: http://www.cs.aau.dk/~nesotto/boost/boost/range/ Notice the library is header only (exception: the adaptor tokenized() depends on Boost.Regex). Writing a review ++++++++++++++++ If you feel this is an interesting library, then please submit your review to the developer list (preferably), or to the review manager. Here are some questions you might want to answer in your review: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With what compiler? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick - reading? In-depth study? - Are you knowledgeable about the problem domain? And finally, every review should answer this question: - 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. Special considerations ++++++++++++++++++++++ Various RangeEx like libraries have been implemented in the past. You might want to compare with those libraries when you form your oppinion: 1. John Torjo's range lib http://rangelib.synesis.com.au/libs/boost-rangelib-20040913.zip http://torjo.com/rangelib/index.html 2. Adobe's ASL libraries include range-based algorithms: http://stlab.adobe.com/group__algorithm.html I'm looking forward to your review. best regards Thorsten, Review Manager

6 12

Crash in boost::gregorian::from_simple_string in BOOST 1.36
by ak1mbox-boost＠yahoo.ca 26 Feb '09

26 Feb '09

Hello, I am using date_time library from Boost 1.36. When running this code: #include <boost/date_time/gregorian/gregorian.hpp> void RunDates() { boost::gregorian::date today(boost::gregorian::day_clock::local_day()); std::string todayString=boost::gregorian::to_simple_string(today); boost::gregorian::date todayFromString(boost::gregorian::from_simple_string(todayString)); } I get a reproducible crash when calling from_simple_string command on the last line of the function. Here is the backtrace: #0 0x961c9a12 in __gnu_debug::_Safe_iterator_base::_M_attach () #1 0x00003029 in __gnu_debug::_Safe_iterator_base::_Safe_iterator_base (this=0xbffff3ac, __seq=0x100698, __constant=false) at debug/ safe_base.h:89 #2 0x00006796 in __gnu_debug ::_Safe_iterator<std::_Rb_tree_iterator<std::pair<std::string const, unsigned short> >, __gnu_debug_def::map<std::string, unsigned short, std::less<std::string>, std::allocator<std::pair<std::string const, unsigned short> > > >::_Safe_iterator (this=0xbffff3ac, __i=@0xbffff35c, __seq=0x100680) at debug/safe_iterator.h:110 #3 0x000068a2 in __gnu_debug_def::map<std::string, unsigned short, std::less<std::string>, std::allocator<std::pair<std::string const, unsigned short> > >::find (this=0x100680, __x=@0xbffff4a4) at debug/ map.h:220 #4 0x00006f11 in boost::date_time::month_str_to_ushort<boost::gregorian::greg_month> (s=@0xbffff4a4) at date_parsing.hpp:68 #5 0x000071cb in boost::date_time::parse_date<boost::gregorian::date> (s=@0xbffff51c, order_spec=0) at date_parsing.hpp:142 #6 0x00007445 in boost::gregorian::from_simple_string (s=@0xbffff51c) at parsers.hpp:35 #7 0x00001f85 in RunDates () at /dates.cpp:18 #8 0x00001e18 in main (argc=1, argv=0xbffff568) at /main.cpp:8 The code was compiled on OSX, gcc version 4.0.1 (Apple Inc. build 5490) with Debug flags, I am linking against dynamic data_time library. Is this a known issue in 1.36 that was fixed in 1.38? going through the list of fixes did not uncover it. The same example compiled with release flags works without problems. I am not certain if this means that I am missing some defines or that release compile misses errors that debug catches. Any help with this is really appreciated! Thank you, Alex

1 0

Question about Spirit architecture
by Bernhard Merkle 26 Feb '09

26 Feb '09

Hi boost developers, The architecture for spirit is documented under http://www.boost.org/doc/libs/1_38_0/libs/spirit/classic/doc/organization.h… my question: should all modules of Core (scanner, primitives, composite, non_terminal) also be independent of each other ? so should they be independent subsystems or are they allowed to have dependencies (within the Core layer) ? thanks for your help kind regards, Bernhard.

3 5