February 2009 - Boost - lists.preview.boost.org

[graph] kolmogorov_max_flow color map, gray state
by Sebastian Nowozin 01 Mar '09

01 Mar '09

Hello everybody, I use the boost graph library to find the linear min-cut of a directed graph with exactly one source and one sink node (s-t min-cut). For this, I setup a linear max-flow problem and solve it using kolmogorov_max_flow. The color_map property is supposed to be usable to recover the edge cut set from the max-flow solution, see the description on http://www.boost.org/doc/libs/1_38_0/libs/graph/doc/kolmogorov_max_flow.html However, as long as there are no vertices colored "gray" I can simply tell which side of the cut a node belongs to by doing something like: std::vector<default_color_type> color(num_vertices(g_ab)); double flow = kolmogorov_max_flow(g_ab, alpha_vertex, beta_vertex, color_map(&color[0])); bool is_left = (color[node_desc] == tc_color_traits::white()); bool is_right = (color[node_desc] == tc_color_traits::black()); And this works just fine. For some problems I am solving there are gray nodes, and I do not know how to determine their position relative to the edge cut set. Is there a code example available in the boost repository or has anyone had this problem? It seems surprising to me that obtaining the edge cut set of a linear min-cut problem seems to be non-trivial using the boost graph library. I must be doing something wrong. Thanks, Sebastian

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Bug in intrusive_ptr,scoped_ptr,scoped_array
by Hansi 28 Feb '09

28 Feb '09

Hello, at least with VS2005 there is a bug in the three smart pointers... If you want to check if the pointer is empty (with unspecified bool) then you get also with NULL a true back. For this the following fix should work: #if defined( _MANAGED ) static void unspecified_bool( this_type*** ) { } typedef void (*unspecified_bool_type)( this_type*** ); operator unspecified_bool_type() const // never throws { return px == 0? 0: unspecified_bool; } #else .... #endif Best regards Hansjörg

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[move] Library uploaded to sandbox
by Ion Gaztañaga 28 Feb '09

28 Feb '09

Hi to all, I've uploaded a new version of the move emulation library to sandbox. I've put it temporarily in "move_semantics" folder to avoid overwriting current move code. I've put some quickbook documentation whose introduction is based in the article "A Brief Introduction to Rvalue References" by Hinnant, Stroustrup, Kozicki. http://svn.boost.org/svn/boost/sandbox/libs/move_semantics/index.html The library needs specially modified Interprocess containers (and Intrusive because of dependences), which I've also uploaded to sandbox. The examples show how movable only values can be inserted into containers. For those that don't like svn sandbox (I'm one of them) I've also put the code and the documentation here: http://www.drivehq.com/web/igaztanaga/move_semantics.zip And online documentation also here: http://www.drivehq.com/web/igaztanaga/libs/move_semantics/ The documentation is not in english, it's in my own english dialect so be careful when reading ;-) Patches and corrections welcome. I've documented some functions to create a little boostbook reference. I've invested some precious time in the library and testing different approaches to see if it plays well with containers but I would like to hear some comments on whether the direction is acceptable and if I should spend more time on it. If someone else with more time wants to continue the library, please do it! ;-) I've personally added to the library all that I've seen useful for move-aware containers, so it might lack some features (move aware algorithms, for example). Anyway, my opinion is that we need some move library, better now than later even if it's too basic, so that we can unify all redundant move emulation that we already have in boost libraries. I hope this is a step in the right direction. Best, Ion

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[threadpool] new version - with rescheduling of current task
by k-oli＠gmx.de 28 Feb '09

28 Feb '09

Hi, I've uploaded a new version of boost.threadpool. It contains a free function this_task_reschedule_until() which lets the current task reschedule until a condition (passed to the fucntion) becomes true. This allows to synchronize with other async events without blocking the worker-thread (thx to Vicente). I've also added two function in order to wait for multiple tasks (it uses Anthonies future lib wait_for_any()/wait_for_all() ). Oliver

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[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

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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.

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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

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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

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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

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[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(); }

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[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

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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

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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

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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.

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[lambda] warning supression
by Steven Watanabe 26 Feb '09

26 Feb '09

AMDG The attached patch allows Lambda's tests to compile with warnings=all warnings-as-errors=on with gcc-4.3.0 msvc8.0express and msvc-9.0express. Ok to commit? In Christ, Steven Watanabe

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[tuple] gcc warnings
by Steven Watanabe 26 Feb '09

26 Feb '09

AMDG I've tested the fix for #2388 and it looks ok. Okay to commit? In Christ, Steven Watanabe

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best way to remove duplicates from forwardIterator [startIter, endIter]
by Sandeep Gupta 26 Feb '09

26 Feb '09

Hi, Given a collection in terms of [startIter, endIter] how can obtain [uniqBeginIter, uniqEndIter] that represents unique elements of the original container. I can always explicitly instantiate a set S of [startIter, endIter] and use [S.begin(), S.end()]. Is it possible to express this in terms of algorithms. Please note that I won't be able to use std::sort as startIter does not conform to RandomAccessIterator. Its a forward iterator. Thanks Sandeep

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Re: [boost] [convert] Default Syntax Idea
by Vladimir.Batov＠wrsa.com.au 26 Feb '09

26 Feb '09

> From: "Stewart, Robert" <Robert.Stewart(a)sig.com> > I was thinking a bit about syntax for the default value for the > notional boost::convert() and kin. How about the following: > > int const i(3); > string const s("something"); > int const j(convert<int>(s) | 5); Yes, this idea is similar to int j = convert<int>(s).or_default(5); but does not introduce new vocabulary (my main hesitation). With the suggested op|, as I am reading it, it makes perfect reading just like I'd read English. And that is usually my criterion for an interface. So, I am voting 'yes'... in principle. See further below. > convert<DestType,SourceType>(SourceType) can return a type which > throws on failure in operator DestType(), but has an operator > |(SourceType) which returns a second type constructed with the > SourceType value. The second type provides its own operator > |(SourceType) which returns that value in its operator DestType() on failure. When the user does not want comprehensive result, it works. The problem as I see it is when the user wants the comprehensive report -- we return two different types, convert1<string, int> j1 = convert<string, int>(s); convert2<string, int> j2 = convert<string, int>(s) | 5; Sometimes I feel we need that as I might like to explicitly check if the call failed without relying on the default convert1<string, int> j1 = convert<string, int>(s) & boost::nothrow; convert2<string, int> j2 = convert<string, int>(s) | 5; if (j1 == 0 && !j1.good()) j1 = 0 but conversion failed if (j2 == 5 && !j1.good()) j2 = 5 but conversion failed Unless we convert both convert1 and convert2 to convert<string, int>::result as convert<string, int>::result j1 = convert<string, int>(s) & boost::nothrow; convert<string, int>::result j2 = convert<string, int>(s) | 5; if (j1 == 0 && !j1.good()) j1 = 0 but conversion failed if (j2 == 5 && !j1.good()) j2 = 5 but conversion failed Or we might simplify that as convert::result<int> j1 = convert::to<int>(s) & boost::nothrow; convert::result<int> j2 = convert::to<int>(s) | 5; if (j1 == 0 && !j1.good()) j1 = 0 but conversion failed if (j2 == 5 && !j1.good()) j2 = 5 but conversion failed The reason I am sticking 'to' in again is that I need the 'convert' as a namespace... or rather as a namespace-like structure: struct convert : mimic_namespace /*I have such a class*/ { template<class TypeOut> struct result { TypeOut value_; bool good_; }; struct internal_with_default { ... }; struct internal_with_no_default { ... }; template<class TypeOut, class TypeIn> internal_with_default<TypeOut, TypeIn> to(TypeIn const&); }; With namespace-like convert structure people will not be able to shortcut 'convert'. I.e. they'll always have to say convert::to which is darn close to convert_to with the advantage of having a dedicated namespace-like place instead of messing inside the boost namespace. Now it seems like I am back where I started. :-) > Returning a default value in lieu of an exception is a special case; > it ought not be treated like formatting. I have an impression that throwing/not-throwing and providing/not-providing the default have to be configured independently. Like I *might* need to throw even if I provide the default: direction dir = convert<string, direction>(str, direction::up) & boost::dothrow; Above I provide the default because I have to (direction does not have the def. ctor). However, I still *might* like to throw on failure. > Thus, while Boost. > Parameter might be appropriate to package the extra information > desired for formatting, I don't like the idea of writing "default_ = > 5" in the call, and I don't think ", 5" in the argument list is as > clear as it could be. I tend to agree with you on both. > The syntax above is obvious and concise while > being distinct from whatever may be done for formatting. You meant to say "laconic", right? Oh, just kidding. Thanks for pointing it out BTW. BTW, what do you think of convert<string, int>(s) & boost::dothrow; instead of convert<string, int>(s) >> boost::throw_t(); People seem to get put off by op>>. Best, V.

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[optional_io] InputStreamable refinement
by Andrew Troschinetz 25 Feb '09

25 Feb '09

This is a spin off from the thread "[lexical_cast] A suggestion" While trying to get lexical_cast and optional to play nice I've run up against some problems with the InputStreamable solution for optional types in optional_io.hpp. The crux of the problem is that I think any given optional type should behave as much like the type it wraps as possible. For example I think this: stringstream sin ("1.2.3.4.5"); optional<double> token; while (sin >> token) cout << token << endl; Should have the same output as this: stringstream sin ("1.2.3.4.5"); double token; while (sin >> token) cout << token << endl; And that this shouldn't fail: stringstream sin ("test"); optional<string> token; sin >> token; // token shouldn't be empty The current InputStreamable solution for optional does not pass these tests. But that's not all, I also believe that there is room for even more improvement here! Since it's semantically valid to have an un- initialized optional type, I think failure to extract something off a stream should return an empty optional type _without_ setting the failbit on the stream. Here's a usage example that demonstrates what I mean by that: // output is "1 nan nan nan nan 5.5 nan nan nan nan nan nan nan -3.2 nan " istringstream sin (" 1 this 5.5 is a test -3.2 a"); optional<double> token; const double nan = numeric_limits<double>::quiet_NaN (); while (sin >> token) cout << token.get_value_or (nan) << " "; // output is "1 " istringstream sin (" 1 this 5.5 is a test -3.2 a"); double token; while (sin >> token) cout << token << " "; I did submit a ticket with the final comment proposing code that is (maybe?) a solution to this refinement. ( https://svn.boost.org/trac/boost/ticket/2659 ) Please pardon any guffaws I made in replies to that ticket, I'm still learning about the nuts and bolts of streams and boost as I go. However there is still one problem, and this brings us back to lexical_cast. Consider this example: int an_invalid_uint = -1; unsigned i = lexical_cast<optional<unsigned> > (an_invalid_uint).get_value_or (0); I believe we should expect this to store 0 in i, but instead it will throw a bad_lexical_cast exception even with my proposed revision to optional_io.hpp. A possible solution is a specialization for optional<Target> somewhere in lexical_cast.hpp that would replace code that looks something like this (pseudocode): do lexical_cast if failed to cast: throw exception With something like this: do lexical_cast if failed to cast: return optional<Target>() So is there any interest in this sort of refinement of optional's InputStreamable implementation or lexical_cast? -- Andrew Troschinetz Applied Research Laboratories

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Extending asio (SCTP support)
by Hal Finkel 25 Feb '09

25 Feb '09

Hello, I've started implementing SCTP support in asio. I would like some feedback on what methodology is preferred. Although I had originally wanted to provide SCTP support as a pure add-on to the current framework, unfortunately, I don't think that can be done. For example, SCTP supports multi-homed endpoints, and the standard API provides a function sctp_bindx which can add and remove endpoint addresses from an active association (connection). While I can provide a subclass of socket_acceptor_service with this extended interface, there is no way of changing the wrapper (detail::reactive_socket_service) used to implement socket_acceptor_service's service_impl_type, and since socket_, protocol_, etc. are private members of detail::reactive_socket_service, I think that there is no way a subclass of socket_acceptor_service can access the underlying socket object. This seems to leave two options: 1. Patch the missing functionality into the existing classes. What worries me is that this approach does not seem to "scale" well with respect to the addition of new protocols. (what happens if someone needs TIPC support, for example). 2. Provide some kind of protocol-specific extension mechanism (templated base classes for example) for detail::reactive_socket_service and other such classes so that it is possible to provide protocol-specific extensions to the base asio interface. Does anyone have a preference on how I proceed? (or is there an option I've missed?) And if some extension mechanism is desired, is there a preference on the technique used for its implementation? Thank you in advance, Hal Finkel P.S. For anyone looking for a quick introduction to SCTP and its associated socket API, I've found HP's SCTP Programmer's Guide (http://docs.hp.com/en/5992-4578/index.html) to be pretty good.

2 2

[geometry] gtl review pre-announcement
by Simonson, Lucanus J 25 Feb '09

25 Feb '09

Fellow geometry authors and interested reviewers, My abstract for gtl has recently been accepted to boostcon. I was unable to put together a geometry panel discussion, however. I am also working on completing documentation for the library by April. I would like the gtl library to be under review during boostcon because I may get the opportunity to meet and talk to some of the reviewers in person. To that end I'd like to ask for volunteers to be review manager and reviewers of the library now so that it isn't a surprise and things can proceed smoothly when the documentation is ready in a few weeks. I especially want other geometry authors to be aware of my plans and schedule. I have the utmost respect for the authors of the other two serious geometry proposals. It is my hope that we can work together during the review process and after to improve and converge our libraries toward the ideal boost::geometry library that all of us can feel proud of. Eventually it is my hope that algorithms in boost::geometry come for a variety of sources selected based upon quality such that there is no single owner of the library, but rather a community. I look forward to your reviews. Thanks, Luke

1 0

Re: [boost] Boost.Convert+Boost.Parameter
by Vladimir.Batov＠wrsa.com.au 25 Feb '09

25 Feb '09

> The keywords are decoupled. > ... > Did you read through the Boost.Parameter tutorial? OK, I admit before I only glanced over the docs a couple of times. I thought I got the idea. Obviously not. :-( Now I printed it out and set down reading. Now I see the registration is all by itself and not coupled with anything. That's good. So, convert() can take those parameters in. Given we do not know how many parameters there might be I'd suggest we set those parameters with operator(). Like convert<string, int>(str)(default_ = -1)(throw_ = false)(some_other_parameter_ = ...) Given, convert() does not know and does not understand "some_other_parameter_" somebody else will need to do something with it. Who would that be and what would it do? I presume we could come up with a Boost.Parameter-based manipulator analog... or... no, I admit I am out of ideas. How can all that work? Thanks, Vladimir.

6 7

[utility] value_initialized fix causes Intel-linux 9.0 compile error
by Niels Dekker - mail address until 2010-10-10 24 Feb '09

24 Feb '09

My fix of the "const incorrectness" of boost::value_initialized (changeset [51355]), committed to the trunk last Friday, has passed the value_init_test tests successfully on most compilers, including intel-linux 10.0 and 10.1: www.boost.org/development/tests/trunk/developer/utility_.html Unfortunately it has a compile time regression failure on intel-linux 9.0, when trying to compare a value_initialized<NonPOD*> and a NonPOD*: error: more than one operator "==" matches these operands: built-in operator "pointer == pointer" built-in operator "pointer == pointer" operand types are: boost::value_initialized<NonPOD *> == NonPOD *const www.boost.org/development/tests/trunk/output/Sandia-intel-9-0-boost-bin-v2-… I don't have access to an Intel compiler, but it looks like the compile error is specific to pointers, as it doesn't seem to occur when comparing value_initialized<T> and T for other types T (int, double, POD, NonPOD). Is this a known compiler bug of the Intel 9.0? Apparently it's fixed by Intel 10.0. The fix of changeset [51355] replaced the existing conversion operator by a pair of them, overloaded for const and non-const. See also https://svn.boost.org/trac/boost/ticket/2548 Would it be okay to just mark the regression failure as "expected", and leave the implementation of boost::value_initialized as it is, including the const-fix? Otherwise, do you have any suggestion for a workaround? Note that the compile error is specific to the implicit use of the conversion operator. value_initialized also provides "get" functions and data() member functions to retrieve its value, which should still work fine on Intel 9.0. Kind regards, Niels -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center

1 0

DynObj - Library for C++ runtime plugin objects
by Arne Steinarson 24 Feb '09

24 Feb '09

I'm the developer of DynObj - a C++ library for cross platform plugin objects/components. In short, the approach of the library is to exploit the underlying compiler representation of virtual function tables. Since the VTable of any type occupies a unique place in memory, the VPTR forms a valid runtime type ID. With the help of this type ID, DynObj (in a host application) can then access type information emitted by the plugin compiler. In effect, we get a cross compiler variant of dynamic_cast<>: * U* do_cast<U*>( T *pt )* This cast operation then takes the role of *QueryInterface(...)* in COM or xpCOM. The difference is that we're not forced into using a specific base class for plugin capable types. We also get a meaningful type system shared across host/plugin, not just isolated interfaces. To go about all of this, the library relies on quite a bit of template code, effectively tracking down object and interface offsets inside classes, and then exporting them in a well defined, binary safe structure. However, to simplify this (there is a bit of 'boiler plate code' needed for each plugin type), DynObj uses a preprocessor that generates most of this, based on a few preprocessing tags embedded in C++ comments. So it is not a 100% compile-time library. Also when using plugins, a fair bit of template code is used, for instantiating objects, smart pointers, executing functions on foreign interfaces and so on. Using plugin objects becomes almost transparent in many cases. More information is available here: http://dynobj.sourceforge.net Now, I wonder if there is any interest from Boost in this type of library. At this time, I'm not eager to do a complete rewrite, since it fills our needs pretty much as it is. If there is some interest, and the basic approach and design is found useful to Boost, I'd be willing to take this some steps further, time permitting. Also, general feedback and experience with the library is appreciated. Best Regards Arne Steinarson, Z-Soft

1 0

[documentation] help - SFINAE confuses doxygen
by Simonson, Lucanus J 24 Feb '09

24 Feb '09

I have noticed after attempting to document my overloaded template functions in doxygen that is simply doesn't work. Doxygen appears to consider all SFINAE overloads of a templated function as a single function, but doxygen's treatment of them is quite erratic. It seems to generally have a bunch of assumptions built into its internal logic about what can't happen in C++ code that aren't valid in my case. Does anyone have any suggestions for how to deal with these issues? I notice that doxygen is used with BoostBook, and I know this must have come up in other libraries. How is it solved? Thanks, Luke

8 14

Re: [boost] Boost.Convert+Boost.Parameter
by Vladimir.Batov＠wrsa.com.au 24 Feb '09

24 Feb '09

Trying to use Boost.Parameter as Daniel showed. Wow, that's truly hairy stuff. Obviously I get it wrong somewhere as matching Parameters constructor cannot be found. I am trying to call int ii = convert_to<int>("1", boost::convert_parameters::default_ = -1); when I have declarations below as (I think) Daniel indicated. namespace convert_parameters { BOOST_PARAMETER_NAME((from_, tag) from_) BOOST_PARAMETER_NAME((default_, tag) default_) } template<class TypeOut, class ArgumentPack> TypeOut test(ArgumentPack const& args) { return TypeOut(); } template< class TypeOut, class TypeIn, class A0> convert<TypeIn, TypeOut> convert_to(TypeIn const& value_in, A0 const& a0) { typedef parameter::parameters<parameter::required<convert_parameters::tag::from_> > Parameters; return test<TypeOut>(Parameters(value_in, a0)); } Any help? Please? Thanks, Vladimir.

3 2

[Phoenix2] nothing is not an actor
by Francois Barel 24 Feb '09

24 Feb '09

Hi, In core/nothing.hpp, "nothing" is defined as: null_actor const nothing = null_actor(); which doesn't make it an actor, rather an "actor base". Shouldn't it rather be defined as something like: actor<null_actor> const nothing = null_actor(); Thanks, François

3 2

Re: [boost] wiki.boost.org Ancient
by David Abrahams 24 Feb '09

24 Feb '09

on Mon Feb 23 2009, DongInn Kim <dikim-AT-osl.iu.edu> wrote: > Hi David, > > Can you setup the DNS of wiki.boost.org to just point to 129.79.245.252 without > aliasing for svn.boost.org? > This cause me difficult to setup its vhost properly. > > For example, > > [root@wowbagger wiki.boost.org]# host wiki.boost.org > wiki.boost.org is an alias for svn.boost.org. > svn.boost.org has address 129.79.245.252 > [root@wowbagger wiki.boost.org]# host beta.boost.org > beta.boost.org has address 129.79.245.252 > [root@wowbagger wiki.boost.org]# I could, but --- and I'm no www expert --- I think there ought to be a redirect so that there's a canonical web address for the wiki. Otherwise you get search engines spidering it twice, etc, no? -- Dave Abrahams BoostPro Computing http://www.boostpro.com

3 2

Re: [boost] Formal Review Request: Boost.Convert
by Vladimir.Batov＠wrsa.com.au 23 Feb '09

23 Feb '09

Stewart, Robert wrote... > I assume that's a reference to me. My suggestion of "conversion" was as a namespace name. > Were you referring to my suggestion of using "converter" for the function object and "convert" > for the function template that would deduce template parameters? Yes, I was referring to that latter suggestion of yours: >> namespace boost >> { >> ...class convert; > s/convert/converter/ ... > template <class TypeOut, class TypeIn> > TypeOut const > convert(TypeIn _input, TypeOut const & _default) > { > return converter<TypeIn,TypeOut>(_input, _default); > } I've essentially implemented function wrappers as you suggested. Only I called them convert_to() and convert_from() that I am hoping many people will be happy with (remembering string_to/from et al) as the names could not be any clearer: int i = convert_to<int>(str); int i = convert_from(str, -1); int i = convert_from<string, double>(str, -1); That allowed me to keep the function object as "convert" and, say, apply it to algorithms as std::transform( strings.begin(), strings.end(), std::back_inserter(integers), convert<string, int>(string(), -1) >> std::hex); which is kinda nice as well. Do you agree? Thanks, Vladimir.

1 0

Re: [boost] Formal Review Request: Boost.Convert
by Vladimir.Batov＠wrsa.com.au 23 Feb '09

23 Feb '09

I've implemented the functionality as I described (convert as a class) and uploaded it as v0.21. I feel it is a considerable step forward in many respects as now it is more of a conversion 'framework' as users can create their specific specializations of boost::convert for their specific needs (as I did with lexical_cast). At the same time it feels reconciliatory as fighting over names could be put to rest (I hope) as we or the users might write simple and generic wrappers to boost::convert. In particular, I added boost::convert_to and boost::convert_from. It's just a suggestion. We might decide to keep them or remove or rename them. I am not fussy about it. So, the deployment loos as follows: // Explicitly specified 'from' and 'to' types. My personal preference int i = boost::convert<string, int>(str, -1); string s = boost::convert<int, string>(-1, "conversion failed"); // Deduced 'from' type. int i = boost::convert_to<int>(str); string s = boost::convert_to<string>(-1); // Both types are deduced. int i = boost::convert_from(str, -1); string s = boost::convert_from(-1, "conversion failed"); Robert suggested renaming 'convert' to 'conversion' but I am not warming up to that (yet, you might have noticed I am slow) as I essentially see 'convert' as a functor, i.e. encapsulating as an action, i.e. a verb is more appropriate. For that reason the code itself looks readable (to me) as "boost::convert<int, string>" reads as 'convert int to string". Thanks, Vladimir.

2 1

[proto] lazy functions in custom domains
by Dean Michael Berris 23 Feb '09

23 Feb '09

Hi Guys, I've recently tried to play around with Boost.Proto and I think I've run into a wall. I was trying to figure this (relatively simple) case out for a while already but it I'm at my wits end not seeing why the implementation doesn't work. I'm pasting the contents of the file (unmodified) which I've tried to follow from the Getting Started document. I was trying to get the custom domain approach working, but I never seem to get the lazy function to be called. The expected result from the code below would be to have multiple lines of output that says "Getting the friends of user # ;)" but I don't see those. There are no compilation errors, and I don't see anything obviously wrong from the implementation and how I understand Lazy functions. I'm just not sure about how lazy functions though can be made part of a domain though -- didn't find anything in the Getting Started guide about it. Help would be very much appreciated (BTW I'm using Proto that's in Boost 1.38.0, building with GCC 4.0 in Mac OSX 10.5.6): ---->8-- #include <iostream> #include <boost/proto/proto.hpp> #include <vector> namespace mpl = boost::mpl; namespace fusion = boost::fusion; namespace proto = boost::proto; using proto::_; using std::vector; using std::cout; using std::endl; struct user_tag; template <class Tag> struct placeholder {}; struct friendster_action_context : proto::callable_context<friendster_action_context const> { uint32_t user_id; friendster_action_context(uint32_t id) : user_id(id) {} friendster_action_context(friendster_action_context const & other) : user_id(other.user_id) {} friendster_action_context & operator= (friendster_action_context other) { other.swap(*this); return *this; } void swap(friendster_action_context & other) { std::swap(user_id, other.user_id); } typedef uint32_t result_type; result_type operator() (proto::tag::terminal, placeholder<user_tag>) const { return this->user_id; } }; template <class Expr> struct friendster_action; struct friendster_action_domain : proto::domain<proto::pod_generator<friendster_action> > {}; template <class Expr> struct friendster_action { BOOST_PROTO_EXTENDS(Expr, friendster_action<Expr>, friendster_action_domain); typedef void result_type; result_type operator()(uint32_t id) const { friendster_action_context ctx; ctx.user_id = id; return proto::eval(*this, ctx); } }; friendster_action<proto::terminal<placeholder<user_tag> >::type> const user = {{}}; struct friend_fun { typedef vector<uint32_t> result_type; template <class T> result_type operator() (T id) const { cout << "Getting the friends of user " << id << " ;)" << std::endl; return result_type(); }; }; template <class Arg> typename proto::result_of::make_expr< proto::tag::function, friend_fun, typename proto::result_of::as_child<Arg const>::type >::type friends(Arg const & arg) { return proto::make_expr<proto::tag::function>( friend_fun(), proto::as_child(arg) ); } #include <algorithm> using namespace std; int main(int argc, char * argv[]) { uint32_t users[] = { 1, 2, 3, 4 }; uint32_t * begin = users; uint32_t * end = users + 4; cout << "Here they are: " << endl; for_each(begin, end, friends(user)); string input; cin >> input; return 0; } ---->8-- -- Dean Michael Berris | Software Engineer, Friendster, Inc. blog.cplusplus-soup.com | twitter.com/mikhailberis | linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis | deanberris.com

2 2

[gil][ublas] Point2DConcept and ublas vector concept
by Christoph Heindl 23 Feb '09

23 Feb '09

Hi, I'd like to use my boost::ublas::bounded_vector types interchangeable with boost::gil::point2 which from my point of view makes totally sense: A convex hull algorithm for 2D would only need to be implemented once (for world coordinates and pixel coordinates) for example. This, however, seems impossible right now because of the differences in their concepts. Is it possible to somehow make a bridge between them (without copying structures)? Any plans to unify those concepts and reuse ublas types? Best regards, Christoph

1 0

Trac tickets: fixed in trunk vs. fixed in release
by Steve M. Robbins 22 Feb '09

22 Feb '09

Hi, For each bug, there are really two levels of "fixed": roughly speaking, the developer considers the issue fixed when it is committed to trunk, while the user considers the issue fixed when it is commited to the release branch. At present, the trac ticket is closed at the first gate. Unfortunately, sometimes the second gate gets forgotten. Could another state be added to the ticket lifecycle to track when it gets merged to release? My aim is to be able to identified "fixed" tickets that are not actually released and, hopefully, to decrease them in number. Maybe there are other ways to achieve this? Regards, -Steve

5 10

[Iterator] Two sets of docs?
by John Maddock 22 Feb '09

22 Feb '09

The iterator library seems to have two sets of docs: one in quickbook format and one in restructured text. Which is the correct up-to-date version, and can we get rid of the other to avoid confusion? Thanks, John.

2 2

[test] [gcc-4.3.2] check_is_close and check_is_small issues
by Dean Michael Berris 22 Feb '09

22 Feb '09

Hi Guys, I have recently upgraded to Boost 1.38 from Boost 1.35 and suddenly I get the following warnings from GCC 4.3.2: ../boost_1_38_0/boost/test/floating_point_comparison.hpp:224: error: 'boost::test_tools::<unnamed>::check_is_close' defined but not used ../boost_1_38_0/boost/test/floating_point_comparison.hpp:246: error: 'boost::test_tools::<unnamed>::check_is_small' defined but not used I have warnings treated as errors in my build and I haven't encountered this issue before. Can this be considered a regression and if yes what can I do to work around it? -- Dean Michael Berris | Software Engineer, Friendster, Inc. blog.cplusplus-soup.com | twitter.com/mikhailberis | linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis | deanberris.com

4 6

[range-ex] generators
by Neal Becker 22 Feb '09

22 Feb '09

I have a question of generate. I believe one usually wants generators to have state. Yet, generator is passed by value. This is awkward, the workaround is to manually specify generate<ForwardRange, Generator&>( rng, gen ); Since Generator is the 2nd template parameter we must specify ForwardRange, which might be complicated. I wonder if we should have: template<class ForwardRange, class Generator> ForwardRange& generate( ForwardRange& rng, Generator & gen );

3 3

[c++0x] OK to merge cpp0x branch config changes to trunk?
by Beman Dawes 22 Feb '09

22 Feb '09

See http://svn.boost.org/svn/boost/branches/cpp0x This branch adds the following config macros: BOOST_NO_CHAR16_T BOOST_NO_CHAR32_T BOOST_NO_CONSTEXPR BOOST_NO_DECLTYPE BOOST_NO_DEFAULTED_FUNCTIONS BOOST_NO_DELETED_FUNCTIONS BOOST_NO_EXPLICIT_CONVERSION_OPERATORS BOOST_NO_EXTERN_TEMPLATE BOOST_NO_RAW_LITERALS BOOST_NO_RVALUE_REFERENCES BOOST_NO_SCOPED_ENUMS BOOST_NO_STATIC_ASSERT BOOST_NO_UNICODE_LITERALS BOOST_NO_VARIADIC_TEMPLATES The particular names were discussed in several threads nearly a year ago. The set of C++0x features detected only covers those available in at least one shipping compiler. Although I've tested locally, I'd appreciate it if someone familiar with Boost.Config could take a look at the branch before the config directories get merged into trunk. --Beman

3 3

[filesystem] security questions
by Sergei Politov 21 Feb '09

21 Feb '09

Hi, In *nix systems it is recommended practice to operate with file descriptors rather than file names. The sample commands sequence is: 1) open file 2) check file status (check symlink for instance) 3) process write operation Unfortunately I cannot find a way to do the same using boost::filesystem API. Is it planned to support such style? Best Regads, Sergei

5 5

[threadpool] new v18
by k-oli＠gmx.de 21 Feb '09

21 Feb '09

Hello, I've uploaded a new version to boost-vault. The new library contains the future library from Anthony Williams (because it seams we don't get boost.future in the next time). regards, Oliver

1 0

Formal Review Request: Boost.String.Convert
by Vladimir.Batov＠wrsa.com.au 21 Feb '09

21 Feb '09

Well, the fishing trip did not work out. :-\ Therefore, I would like to request a formal review for the Boost.String.Convert functionality. I've uploaded the file called boost-string-convert.zip to the Vault (http://www.boostpro.com/vault/index.php) It has the conversion-related header, the test/usage executable and the documentation (MS Word, HTML). Compiled on Linux and Visual Studio 2008. At the bottom is the "motivation" introductory section from the docs. There is very little of actually code, so you might just read it rather that suffering through my document mumble. Currently-known issues. 1) The attention was given to the behavior (to provide simple/advanced conversion-failure check, throw/no-throw behavior, locale, formatting) and not to the efficiency. I am sure people will come up with ways to run this damn thing much faster. I am very much looking forward to your contributions as I do not really feel I am any good at it. 2) I've implemented the recently suggested boost::stirng::convert() interface but that might need some additional work to handle corner cases correctly. I promise to look into it in due course. I would like to thank everyone participated in the lexica_cast and boost::string::convert-related discussions and expressing their views and opinions and coming up with suggestions. All of them were heard, considered and much and truly appreciated. I apologize if in the end it does not look out as you might like to see it. I swear, your contributions were not in vain. Thanks, Vladimir. Motivation I had a need for a convenient and uniform facility to convert values to and from a literal textual form. Such a need is common when converting between internal (to a program) data types and their external representations. Typical applications would be reading of configuration files, packing and unpacking internal data to and from, say, XML, etc. The boost::lexical_cast looked very promising and was the preferred solution compared to others (such as C functions, std::stringstream, etc., see the lexical_cast documentation for more discussion about alternatives). Unfortunately, I needed functionality beyond what lexical_cast was providing (configurable throw/no-throw behavior, formatting support, locale support, etc.). After discussions on the Boost developers list and with the lexical_cast author (Kevlin Henney) and the maintainer (Alexander Nasonov) it was collectively decided that the required functionality extensions were not compatible with the idea of what lexical_cast embodied and a more dedicated family of conversion functions with richer interfaces was needed. That decision resulted in the development of the following header-only string-conversion library described in this document: boost::string::convert() The interface is explicit about its purpose ? string-related -- string-to-type and type-to-string -- conversions. It builds on the lexical_cast past experience, offers the already familiar conversion functionality and more: · throw and no-throw conversion-failure handling behavior; · support for the default value to be returned when conversion fails; · formatting support based on the standard (or user-defined) manipulators (like std::hex, std::scientific, etc.); · locale support; · support for various (boost::range-compliant) char and wchar_t-based containers (std::string, std::wstring, char const*, wchar_t const*, char array[], std::vector<char>, etc.); · no DefaultConstructibility requirement for the Target type; · room to grow.

12 73

GMANE gateway to the Boost Users mailing list seems dead
by Vladimir Batov 21 Feb '09

21 Feb '09

... as its overall traffic

2 1

Re: [boost] Formal Review Request: Boost.Convert
by Andrzej Krzemienski 21 Feb '09

21 Feb '09

Hi, I would like to propose removing the default value for the second argument of convert. I believe it may be insecure. Let me explain it by exemple. What did I mean when I wrote the following code: string str = readInput(); int men = convert_to<string, int>(str); 1. I meant: "if conversion is impossible, return 0", because I read the documentation thoroughly. 2. I am a novice and didn't really think about the situation where someone types a non-int string. In case of the first option it is all fine, but if the latter is the case, it may have been better to throw an exception to the user. I would propose, rather than having a default "fallback" value to provide two overloads for convert: one with two parameters where you can provide the fallback value, and the other, one-parameter, that would indicate that you want to throw an exception on failure. Yo do not loose much of your original interface, because you can write more explicitly: int men = convert_to<string, int>(str, 0); I find it better because: 1. It forces the writer to type more clearly his intentions. (Or explicitly confirm that he is aware that the string may not be convertible to int.) 2. Releaves you from providing the throw_t argument altogether. This in turn removes the possibility of writing: convert<string, int>(str, -1) >> throw_t(); // What does -1 mean here? Regards, &rzej

2 2

[utility] A fix for the const issue of value_initialized
by Niels Dekker - mail address until 2010-10-10 20 Feb '09

20 Feb '09

The boost::value_initialized<T> utility has a major issue regarding const-correctness: It has a const-qualified conversion operator, returning a non-const reference to the T object it owns. I have already created a ticket, <https://svn.boost.org/trac/boost/ticket/2548>, and mailed Fernando Cacciola (the author of value_initialized) on this issue. He agrees that it should be fixed, and he allows me to do so. The patch I've attached to the ticked replaces the current conversion operator by two of them, overloaded for const and non-const access: operator T const &() const { return this->data(); } operator T&() { return this->data(); } The patch also fixes value_initialized::data() in a similar way. Please let me know if you have any problem with the patch. Otherwise I'd like to apply it to the trunk by the end of the week: https://svn.boost.org/trac/boost/attachment/ticket/2548/value_initialized_c… Note that the issue has been discussed here already five years ago: http://lists.boost.org/Archives/boost/2004/01/59987.php At that time, some non-conforming compilers couldn't deal with conversion operators overloaded for const and non-const access. But now I've tested the value_initialized patch on a few compilers (MSVC 2003, MSVC 2008, CodeGear), and they all succeeded. After the commit, I'll keep a close look at the regression page, of course. Kind regards, Niels -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center

1 1

[ignore this] Hello?
by Andrey Semashev 20 Feb '09

20 Feb '09

test

1 0

[any] Multimethod for boost::any and modified boost::any to fit multi method
by nowake＠fiercewinds.net 20 Feb '09

20 Feb '09

Hi All. I create multi method for boost::any using Modern C++ Design's multi method technique. It can dispatch method dynamically like this: _________________________________________________________________________ struct T1 { string operator()(int value) const { return string("T1(int)"); }; string operator()(double value) const { return string("T1(double)"); }; string operator()(A value) const { return string("T1(A)"); }; }; // "entry" to Multi method bool t10(Multimethod::entry<any, any, T1, int>()); bool t11(Multimethod::entry<any, any, T1, double>()); bool t12(Multimethod::entry<any, any, T1, A>()); struct T2 { string operator()(int value) const { return string("T2(int)"); }; }; // "entry" to Multi method bool t20(Multimethod::entry<any, any, T2, int>()); BOOST_AUTO_TEST_CASE(test04) { any m((T1())); any a(0); BOOST_CHECK_EQUAL( any_cast<string>(Multimethod::apply<any>(m, a)), "T1(int)"); a = 0.0; BOOST_CHECK_EQUAL( any_cast<string>(Multimethod::apply<any>(m, a)), "T1(double)"); a = A(); BOOST_CHECK_EQUAL( any_cast<string>(Multimethod::apply<any>(m, a)), "T1(A)"); m = T2(); a = 0; BOOST_CHECK_EQUAL( any_cast<string>(Multimethod::apply<any>(m, a)), "T2(int)"); }; __________________________________________________________________________ If you are interested in this multi method, please see #2749 for detail. https://svn.boost.org/trac/boost/ticket/2749 Thanks, Nowake

4 10

[asio] two-lock queue deadlocks?
by Dean Michael Berris 20 Feb '09

20 Feb '09

Hi Guys, I've run into an issue with defining BOOST_ASIO_ENABLE_TWO_LOCK_QUEUE when using Boost.Asio in Boost 1.38.0. I'm currently implementing an asynchronous HTTP client and when I wanted to try the experimental feature and on a single-core machine apparently I run into a deadlock when the asynchronous handler is itself posting to the same io_service queue that hosted it. Is this a known issue with BOOST_ASIO_ENABLE_TWO_LOCK_QUEUE, or is this a usage issue? -- Dean Michael Berris | Software Engineer, Friendster, Inc. blog.cplusplus-soup.com | twitter.com/mikhailberis | linkedin.com/in/mikhailberis | profiles.friendster.com/mikhailberis | deanberris.com

1 0

[asio] Received 3 times RST, ACK before the boost TCP returns connection failure
by allen han 20 Feb '09

20 Feb '09

Hi: Pretty new to use the boost library for networking and experienced a problem to use the TCP socket on client side. 1. using the call below to connect server: mSocket.async_connect(endpoint,boost::bind(&handleConnect, this, boost::asio::placeholders::error, ++aEndPointIterator)); 2. found connection is failed, then close the socket void handleConnect(const boost::system::error_code &aErr, boost::asio::ip::tcp::resolver::iterator aEndPointIter) { if (!aErr) { ... } else if (aEndPointIter != boost::asio::ip::tcp::resolver::iterator()) { doClose(); ... } else { ... doClose(); } } 3. From Ethereal, found that SYN, RST/ACK have been sent 3 times before the connection is closed, Client sent Server SYN, Server sent Clinet RST, ACK Client sent Server SYN, Server sent Clinet RST, ACK Client sent Server SYN, Server sent Clinet RST, ACK Question: Any flag to inform the boost TCP stack to return error if it receives the first RST,ACK?

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[1.38] PDF docs release candidate available
by John Maddock 19 Feb '09

19 Feb '09

The release candidate for the PDF build of the 1.38 docs is now available from http://boost.cowic.de/rc/pdf/, unless anyone spots any last minute issues, I'll put these on sourceforge at the weekend. Enjoy, John.

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[date_time] How to build the docs?
by John Maddock 19 Feb '09

19 Feb '09

Am I correct in thinking that the date_time docs need some manual intervention to build correctly? Any instructions? Thanks, John.

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[fusion] C++0x support?
by Ein Held 19 Feb '09

19 Feb '09

Hello is there any chance for c++0x support (rvalue forwarding for the containers' constructors and operator=s' in particular) for fusion in 1.39? Thank you

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