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[Spirit Qi] Failed to parse the following fixed format double
by Michael Powell 19 Jan '19

19 Jan '19

Hello, We've been here before, but it is still a problem. I formatted this one using Boost.Format, "%1$.20f", especially dealing with 64-bit floating point values: "-6454866677007257221799838306103363329054216765979693126687924767750184064408021645577150612734391912932504859271476290909819606665305867922002041825515395649967939044362235953753132737391831714484437364695236622971838510661738713863719312223765488747173369566663518205119012003640541309414736378162701139968.00000000000000000000" Grammar is defined: numeric_sign %= ( ('-' >> attr(numeric_sign_minus)) | ('+' >> attr(numeric_sign_plus)) ) ; float_lit %= real_parser<float_t, strict_ureal_policies<float_t>>{}; floating_point %= -numeric_sign >> float_lit; With rules defined as: qi::rule<iterator_type, numeric_sign_t()> numeric_sign; qi::rule<iterator_type, float_t()> float_lit; qi::rule<iterator_type, floating_point_number_t()> floating_point; Where float_t is a defined part of the AST: using float_t = double; And floating_point maps to the floating_point_number_t, basically mapping the Sign and Value. Seems like we've been here before with inadequate response, however, reading the Boost documentation, I do not see any reason any Qi should be rejecting this value: https://www.boost.org/doc/libs/1_69_0/libs/spirit/doc/html/spirit/qi/refere… Particularly the RealPolicies: sign = lit('+') | '-' ; nan = -lit("1.0#") >> no_case["nan"] >> -('(' >> *(char_ - ')') >> ')') ; inf = no_case[lit("inf") >> -lit("inity")] ; floating_literal = -sign >> ( nan | inf | fractional_constant >> -exponent_part | +digit >> exponent_part ) ; fractional_constant = *digit >> '.' >> +digit | +digit >> -lit('.') ; exponent_part = (lit('e') | 'E') >> -sign >> +digit ; Although the concern I have is that the RealPolicy grammar defined above is not implemented as Qi Rules, per se, but rather brute force. In other words, error prone in the ways that a brute force approach is error prone. Best regards, Michael Powell

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[Format] How to format floating point values
by Michael Powell 19 Jan '19

19 Jan '19

Hello, How do I format floating point values, either double or float? I want to specify things like the precision during the formatting, i.e. how many digits to include in the fractional digits, and so forth. Currently, I am using this, for instance: General: "%1$g" Fixed: "%1$f" Scientific: "%1$e" or "%1$E" (depending on whether lower or upper case, respectively) Thanks! Best regards, Michael Powell

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is boost::container::static_vector header only library?
by Sivaram L 19 Jan '19

19 Jan '19

I am working on a embedded systems project, where we are exploring options to use STL containers without dynamic memory allocation, except std::array we cannot use any of the STL, boost container has static_vector for that, on browsing the code,we found that the library has to be built, is there a way to use this library as header only library?

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Atomic boost::filesystem::rename
by Lars 15 Jan '19

15 Jan '19

Hello, What is the most "atomic" way to move two files from a local disk to a server location? The meaning of atomic in this context means that either both files are moved or both files stay in original location. No intermediate files should be present once operation is finished. The two files are located in different directories; /root/file_a /root/data/file_b The solution must support both Windows and Linux environment. It appears boost::filesystem::rename(..) uses Win32 API MoveFileExW for the Windows implementation. The documentation for MoveFileExW states; "If the file is to be moved to a different volume, the function simulates the move by using the CopyFile and DeleteFile functions. If the file is successfully copied to a different volume and the original file is unable to be deleted, the function succeeds leaving the source file intact." This means boost::filesystem::rename(..) could potentially just perform a file copy which is undesirable behaviour. Our understanding is that Boost filesystem does not contain ACL permission support [1] which make it difficult to check privileges prior to performing moves. Appreciate any input on the matter. Using C++14 and Boost. [1] - https://lists.boost.org/boost-users/2018/12/89232.php

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Re: [Boost-users] Server application won't bind to ports on IP address other than my internal ones
by Osman Zakir 15 Jan '19

15 Jan '19

I just tried commenting out the POST request handling code and the client_session stuff, and then tried to run it with my external IP, but the same error from bind() came up saying that the requested address is not valid in its context. I also tried using the wildcard IP 0.0.0.0 as the command line argument for the address when running the server and entering my external IP into the browser address bar, but I still couldn't visit the app in the browser (can't get to it either way). The problem is probably in the server code, and is because of Asio (probably). I need some advice on how best to confirm this and troubleshoot the problem. Thanks in advance.

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C++Now 2019 Submission Deadline
by Jon Kalb 14 Jan '19

14 Jan '19

The deadline for submitting to C++Now 2019 is just a few days away. If you’ve been thinking of submitting, please do not delay: http://cppnow.org/announcements/2018/12/2019-call-for-submissions/ <http://cppnow.org/announcements/2018/12/2019-call-for-submissions/> Thanks. Jon

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Boost.Optional error should be a warning
by Michael Powell 14 Jan '19

14 Jan '19

Hello, I am using Boost.Optional, and, while I do want to "include it in an output", the library which I am doing so has another mechanism to do so. Translation, for Optional purposes, the following assertion should be a warning, IMO, and not an error: BOOST_STATIC_ASSERT_MSG(sizeof(CharType) == 0, "If you want to output boost::optional, include header <boost/optional/optional_io.hpp>"); Cheers, Michael Powell

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Boost.Units: Is it possible to convert on assignment without casting?
by Carel Combrink 14 Jan '19

14 Jan '19

Hi. I have two unit quantities defined as follow: static const auto Hz = boost::units::si::hertz; static const auto KHz = boost::units::si::kilo * Hz; using Hertz = boost::units::quantity<decltype( Hz ), double>; using Kilohertz = boost::units::quantity<decltype( KHz ), double>; Assigning one type to another does not compile: Kilohertz freqKhz = Kilohertz::from_value( 1.234 ); Hertz freqHz = freqKhz; >>> error: conversion from 'Kilohertz {aka boost::units::quantity<...>, double>}' to non-scalar type 'Hertz {aka boost::units::quantity<...>, double>}' requested [1] Is this possible, should it be enabled or is it not supported? I am using boost 01.67, Mingw 5.3 and MSVC 2017 (C++14) The following options work as expected: Hertz freq1 = static_cast<Hertz>( freqKhz ); Hertz freq2 = Hertz( freqKhz ); But this adds a bit more code to maintain and keep in sync, one thing one tries to avoid when using the library since one needs to keep the LHS and the RHS of the opertor= in sync. PS: The chrono library allows this type of conversion given there is no information lost (but for double as storage types this should not be the case) std::chrono::seconds sec = std::chrono::seconds { 10 }; std::chrono::nanoseconds nsec = sec; [1] https://gcc.godbolt.org/z/0sTHQQ Regards, Carel

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Forcing boost to build zlib
by Simon Michalke 12 Jan '19

12 Jan '19

Hello, what is needed to force bjam to build zlib? Is the zlib.h enough? Also is there a way to make bjam fail compiling if I set "NO_ZLIB=0" and it does not find the zlib.h / source? It is really inconvenient that bjam silently switches off zlib without any error or warning why zlib is not being build. My commands are: ./bootstrap.sh --without-libraries=python --prefix=/home/simon/code/cfs/release_mingw_openblas/cfsdeps/boost/install --with-toolset=gcc --without-libraries=context --without-libraries=coroutine target-os=windows architecture=x86 address-model=64 release and ./b2 target-os=windows architecture=x86 address-model=64 release --user-config=user-config.jam toolset=gcc-mingw -s ZLIB_BINARY=\"/home/simon/code/cfs/release_mingw_openblas/lib64/MINGW_X86_64/libzlibstatic.a\" -s ZLIB_INCLUDE=\"/home/simon/code/cfs/release_mingw_openblas/include\" -s NO_ZLIB=0 threading=multi install (this is cross compiling, but I have the same problem building for Linux) Regards, Simon

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Possible Boost.Variant issue with JSON AST
by Michael Powell 11 Jan '19

11 Jan '19

Hello, I've got an AST I am developing to support JSON parsing using the latest VC++ (15.9.5), however, I am having difficulty persuading the compiler with my forward declarations. i.e. 1>d:\dev\boost.org\boost_1_69_0\boost\mpl\sizeof.hpp(27): error C2027: use of undefined type 'kingdom::json::object_t' In terms of JSON AST modeling, the rub appears to be in a couple of places: defining the JSON AST Array, and making the JSON AST Object available to Value. Re: semantic terminology, Value is interchangeable with Element, in view of the JSON grammar. Here's my attempt at a flattened single source example: https://wandbox.org/permlink/83c3VXZ4W1DHoEBc I seem to recall there being future issues with C++ forward declarations, but this seems to be like a bad language design decision to restrict this, especially in light of this kind of approach. I'm not sure how better to sort this out. At minimum, at least Value needs a forward declaration depending on how I arrange my headers, includes, etc. But then I still run into Value forward declaration undefined type issues. I'm not sure it's as much a language issue as much as it is possible a Boost.Variant issue, per se. Suggestions? Thanks! Michael Powell

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