August 2012 - Boost-users - lists.boost.org

[Program Options] terminate parsing after first positional argument
by Stuart Pook 22 Jan '13

22 Jan '13

Hello, How can I tell Boost Program Options to stop parsing the arguments as soon as it finds a positional argument? I'd like to be able to parse the argument list "-v chmod -R -v 600 foo" as having one argument for my program (-v) and the rest as a std::vector of std::string (including the -v). In the attached program I have tried 2 different approaches. The first uses multitoken with the arguments "--command date -u -v", it fails because "-u" isn't known. The second uses collect_unrecognized with "chmod -R -v 600", it doesn't work because -v is interpreted by boost and doesn't end up in the vector. As someone said back in 2005, perhaps I'm trying to write xargs: http://thread.gmane.org/gmane.comp.lib.boost.user/9529/focus=9641 I know that I can ask my users to write a.out -v -- chmod -R -v 600 foo but I don't want to do that. I want them to write "a.out -v chmod -R -v 600 foo". The first positional argument should should tell boost to stop processing. Another slightly different question. If I have a multitoken option that takes doubles how can I get it to accept negative values? If I give my program "--floats 1 8 -4 6" where --floats starts a multitoken option that accepts double, I get an exception saying that "-4" is an unknown option. thanks Stuart This is what my test program gives me with boost 1.50: argv: dd --command date -u -v unrecognised option '-u' Allowed options: -v [ --verbose ] verbose --command arg command to run 2nd try argv: dd chmod -R -v 600 I'm verbose v: chmod -R 600 3rd try argv: dd --floats 1 8 -4 6 unrecognised option '-4' Allowed options: -v [ --verbose ] verbose -f [ --floats ] arg numbers and my program (formatted to fit in 80 characters) #include <boost/program_options.hpp> #include <boost/range/algorithm.hpp> #include <boost/program_options/parsers.hpp> #include <boost/program_options/options_description.hpp> #include <iostream> namespace po = boost::program_options; #define nelements(a) (sizeof (a) / sizeof (a)[0]) void print(char const * * b, char const * * e) { std::cout << "argv: "; std::copy(b, e, std::ostream_iterator<char const *>(std::cout, " ")); std::cout << std::endl; } int main(int argc, char ** argv) { { bool verbose; std::vector<std::string> command; po::options_description desc("Allowed options"); desc.add_options() ("verbose,v", po::bool_switch(&verbose)->default_value(false), "verbose") ("command", po::value<std::vector<std::string> >(&command) ->multitoken(), "command to run") ; char const * args[] = { "dd", "--command", "date", "-u", "-v", 0 }; print(args, args + nelements(args) - 1); po::variables_map vm; try { po::store(po::command_line_parser(nelements(args) - 1, args) .options(desc).run(), vm); po::notify(vm); if (verbose) std::cout << "I'm verbose\n"; std::cout << "command: "; boost::copy(command, std::ostream_iterator<std::string>(std::cout, " ")); std::cout << std::endl; } catch (boost::program_options::unknown_option & x) { std::cerr << x.what() << "\n" << desc << "\n"; } } std::cout << "2nd try\n"; { bool verbose; po::options_description desc("Allowed options"); desc.add_options() ("verbose,v", po::bool_switch(&verbose)->default_value(false), "verbose") ; char const * args[] = { "dd", "chmod", "-R", "-v", "600", 0 }; print(args, args + nelements(args) - 1); po::variables_map vm; po::parsed_options parsed = po::command_line_parser(nelements(args) - 1, args). options(desc).allow_unregistered().run(); try { po::store(parsed, vm); } catch (boost::program_options::unknown_option & x) { std::cerr << x.what() << "\n" << desc << "\n"; exit(2); } po::notify(vm); if (verbose) std::cout << "I'm verbose\n"; std::cout << "v: "; std::vector<std::string> v = po::collect_unrecognized( parsed.options, po::include_positional); boost::copy(v, std::ostream_iterator<std::string>(std::cout, " ")); std::cout << std::endl; } std::cout << "3rd try\n"; { bool verbose; std::vector<double> f; po::options_description all("Allowed options"); all.add_options() ("verbose,v", po::bool_switch(&verbose)->default_value(false), "verbose") ("floats,f", po::value<std::vector<double> >(&f)->multitoken(), "numbers") ; char const * args[] = { "dd", "--floats", "1", "8", "-4", "6", 0 }; print(args, args + nelements(args) - 1); po::variables_map vm; try { po::store(po::command_line_parser(nelements(args) - 1, args) .options(all).run(), vm); po::notify(vm); if (verbose) std::cout << "I'm verbose\n"; std::cout << "floats: "; boost::copy(f, std::ostream_iterator<double>(std::cout, " ")); std::cout << std::endl; } catch (boost::program_options::unknown_option & x) { std::cerr << x.what() << "\n" << all << "\n"; } } }

6 16

[units] Missing quantity operator++, operator%
by Nathan Crookston 25 Oct '12

25 Oct '12

All, I'm in the process of switching my homegrown units system over to boost units. Some operators which I'm missing are the modulus and the pre and post increment operators. Looking through the archives I note an original review[1] which mentioned the absence of those operators. One response claimed that quantity<si::length, int> t = 5. ...; t++; was nonsensical as writing 5 m + 1, and the reviewer eventually agreed, citing possible confusion if the quantity type converted the initializer. Matthias Schabel seemed to respond favorably: 'I debated this for a while - the only problem is that there will be some value types with heterogeneous operator+ / operator- for which q + 1 is not the same type as q, but I guess that it is just OK for it to just give a compile error in those cases.' And Steven Watanabe said 'Will do.' I haven't found anything regarding the modulus operator. My question is, would a patch adding those operators be accepted? Thanks, Nate [1] http://lists.boost.org/Archives/boost/2007/03/119001.php

3 4

Asio and ZeroMQ
by Matthias Vallentin 11 Oct '12

11 Oct '12

A while ago, Maciej Gajewski started an effort to use Asio to observe a ZeroMQ socket [1]. Based on his code, I put together a thin library that wraps the implementation details. Since other have requested a working example, here it is now at github: https://github.com/mavam/bmq Any feedback is highly appreciated. A basic usage example looks like this: #include <boost/asio/io_service.hpp> #include <bmq.h> int main() { boost::asio::io_service io; bmq::context ctx(1); bmq::component c(ctx, io); auto sink = c.add_sink(ZMQ_PAIR, "inproc://x"); c.subscribe(sink, [](bmq::message&& msg) { std::string str(static_cast<char*>(msg.data()), msg.size()); std::cout << str << std::endl; }); auto source = c.add_source(ZMQ_PAIR, "inproc://x"); bmq::message msg(const_cast<char*>("foo"), 3, nullptr); source->send(msg); // Execute message handler. io.poll(); return 0; } At this point, the library is really thin and only provides very rudimentary wrapping of ZeroMQ. In the future, I plan to extend it in order to facilitate applications that build on message-passing. The dataflow abstraction I envision is essentially a directed graph, where nodes represent components and edges communication links. 0mq provides the edges and the Asio handles asynchronous event processing at the component level. The motiviation is that this model lends itself well for scaling out distributed systems over large clusters. Matthias [1] http://permalink.gmane.org/gmane.network.zeromq.devel/9538

4 4

[Sandbox - endian] Why is endian still in sandbox?
by Nathaniel J Fries 07 Oct '12

07 Oct '12

A fairly novel (at least when put up against more intricate labours like asio, filesystem, and their like) project which appears to be finished and would be a very useful companion to existing libraries sits in the sandbox. Is there a reason for this?

3 3

[BGL] vecS for vertex container and vertex index adjustments
by Sergey Mitsyn 03 Oct '12

03 Oct '12

Hi all, I know that while using vecS for vertices one has no vertex iterator stability upon removing vertices. But I have a question if there exists something like vertex _index_ stability. The documentation says that indices for vertices are automatically adjusted so that they are still in contiguous range, but it is not specified how it is done. Is it okay to assume that if a vertex with an index I is removed, then vertices with indices < I have their indices unchanged, while vertices with indices > I have their indices decreased by one? The actual problem is removing all vertices meeting some condition. Is the following code ok? // traverse all vertices and remove those for which predicate // condition_to_remove_vertex returns true. // graph is adjacency_list<.., vecS, ...> vertex_iterator vi = vertices(graph).first, vi_end = vertices(graph).second; while (vi != vi_end) { if (condition_to_remove_vertex(vi, graph)) { vertices_size_type end_index = vertex_index[*vi_end] , vi_index = vertex_index[*vi]; remove_vertex_f(*vi, graph); // vi and vi_end are invalid --end_index; vi = vertices(graph).first + vi_index; vi_end = vertices(graph).first + end_index; // now vi and vi_end are valid again } else ++vi; } This way seems to be more effective than to start iteration again every time a vertex is removed. ------------ Sergey Mitsyn.

3 14

[boost.build] Problems getting PDB files withs DLLs
by Jonathan Jones 19 Sep '12

19 Sep '12

Hi all, I'm having problems getting PDB files built with the DLLs using Boost 1.49 and Visual Studio 2010. I have both debug-symbols=on and debug-store=database specified, but the PDB files are never built. Am I missing something? Thanks, Jon

1 1

[boost] [contract] static_assert in contracts or not?
by Lorenzo Caminiti 17 Sep '12

17 Sep '12

Hello all, If static assertions make sense within contracts (preconditions, postconditions, and class invariants) is a questions that has been raised by both Vicente and Andrzej. I don't have a definitive answer so I'd like to discuss with the ML. On Wed, Aug 29, 2012 at 2:48 PM, Andrzej Krzemienski <akrzemi1(a)gmail.com> wrote: > (6) > Static assertions: is there any value in providing them, given that we > already have this ability in Boost? I see that N1962 decided to abandon > them; I am pretty sure the reason was that static_assert was already there. > They somehow do not fit conceptually into the model of preconditions, > postconditions and invariants. Precondition, for instance tries to detect a > run-time condition occurring immediately before a function is called this > time. Static assertion is not even executed then. What point is there in > putting such assertion into the precondition? Documentation says " static > assertions can be selectively disabled depending on where they are > specified [...] so it is still important to logically associate them with > preconditions, postconditions, etc." -- technically this sentence makes > logical sense, but can you think of a single example where this selective > disabling of assertions would be useful? What is the point in disabling > such assertions at all, if they cost you nothing in run-time? I propose to > remove them and give a sort of recommendation that software quality is > assured by using a number of fairly independent tools: DbC, concepts, > static assertions. I think we can break down the question in two parts. Let's assume N1962 is accepted into C++1x so we have both contracts and static_assert. 1) Would you expect to be able to use static_assert within contract assertions (preconditions, postconditions, and class invariants)? Note that only boolean conditions are allowed by N1962 within contracts, general code is not allowed, therefore this is not a trivial question. For example, would you expect to be able to do the following option A: template< typename To, typename From > To* memcopy ( To* to, From* from ) precondition{ static_assert(sizeof(To) >= sizeof(From), "destination too small"); static_assert(boost::is_convertible<From, To>::value, "incompatible types"); to; // pointer not null from; // pointer not null } { // ... } In this case, would it ever make sense to use static_assert in postcondition and/or class invariants even if that were allowed? Or would you just use static_assert in the body, option B: template< typename To, typename From > To* memcopy ( To* to, From* from ) precondition{ to; // pointer not null from; // pointer not null } { static_assert(sizeof(To) >= sizeof(From), "destination too small"); static_assert(boost::is_convertible<From, To>::value, "incompatible types"); // ... } I don't like this because the assertions are about the specifications (they assert a requirement of the interface) so they should go in the declaration and not in the implementation. Or maybe the assertions should be represented as concept requirements on To and From, option C: template< typename To, typename From > requires SizeofGreaterEqual<To, From>, Convertible<From, To> To* memcopy ( To* to, From* from ) precondition{ to; // pointer not null from; // pointer not null } { // ... } (Only we don't have concepts...) 2) Let's assume, we answered option A to question 1): template< typename To, typename From > To* memcopy ( To* to, From* from ) precondition{ static_assert(sizeof(To) >= sizeof(From), "destination too small"); static_assert(boost::is_convertible<From, To>::value, "incompatible types"); to; // pointer not null from; // pointer not null } { // ... } Would you expect these static_asserts to be disabled when precondition compilation and checking is turned off at compilation time? I'd think so. Thanks. --Lorenzo

3 2

Fusion error: wrong number of template arguments (30, should be 20)
by Joost Kraaijeveld 11 Sep '12

11 Sep '12

Hi, I have the following error after an upgrade to Boost 1.49 (Debian Wheezy): /usr/include/boost/fusion/container/deque/detail/preprocessed/deque_initial_size30.hpp:14:196: error: wrong number of template arguments (30, should be 20) In file included from /usr/include/boost/mpl/aux_/include_preprocessed.hpp:37:0, from /usr/include/boost/mpl/vector.hpp:46, from /usr/include/boost/fusion/container/deque/detail/deque_initial_size.hpp:16, from /usr/include/boost/fusion/container/deque/deque.hpp:15, from /usr/include/boost/fusion/container/deque.hpp:11, from /usr/include/boost/fusion/container.hpp:14, from ../../../library/../include/Danu/DanuModelObjects/Login.hpp:12, from ../../../library/DanuModelObjects/Login.cpp:7: /usr/include/boost/mpl/aux_/preprocessed/gcc/vector.hpp:22:8: error: provided for 'template<class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15, class T16, class T17, class T18, class T19> struct boost::mpl::vector' I have defined the following: #define FUSION_MAX_VECTOR_SIZE 30 #define FUSION_MAX_MAP_SIZE 30 How can I solve this problem? TIA -- Groeten, Joost Kraaijeveld Askesis B.V. Molukkenstraat 14 6524NB Nijmegen tel: 024-3888063 / 06-51855277 fax: 024-3608416 web: www.askesis.nl

3 7

[Range] insert algorithm fails if target is a map
by Robert Jones 11 Sep '12

11 Sep '12

The title says it all really. The failure occurs because the insert algorithm expects the container to provide a 3-arg insert of the form container.insert( position, begin, end ); whereas map's, multimap's and set's insert method only takes two arguments... map.insert( begin, end ); Is this limitation by design? It would be easy to provide specialisations for maps, mmaps and sets, but that would not be a completely general solution. - Rob.

3 3

Boost.Hash and enums
by Filip Konvička 07 Sep '12

07 Sep '12

Hi, In Boost 1.51, it looks to me like boost::hash_value no longer knows how to handle enums anymore. Is the following the right way to tell it to treat enums like ints? #if (BOOST_VERSION >= 105100) // Boost 1.51.0+ namespace boost { /// Enable hashing of enums. template<typename E> size_t hash_value( E const e, typename std::enable_if<std::is_enum<E>::value, E>::type def = static_cast<E>(0)) { return hash_value((int)e); } } #endif Is enum hashing support going to be added to the library in the future? Thanks, Filip

3 5