January 2019 - Boost-users - lists.preview.boost.org

C++Now 2019 Registration is Open
by Jon Kalb 24 Jan '19

24 Jan '19

Boosters, Registration for C++Nows 2019 (aka BoostCon) is now open: http://cppnow.org/announcements/2019/01/2019-registration-is-open/ Please help us to spread the word about this announcement. Thanks. Note that the Aspen Meadows Resort online registration link is also up on the lodging page. Because there will be another group in the hotel, we’ve been allocated fewer rooms this year. Please either reserve a room very soon or plan to stay at the Lamplighter or another hotel in town. See you in Aspen in May. Jon

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[Format] Formatting some string chars not encoding to hex
by Michael Powell 22 Jan '19

22 Jan '19

Hello, I've got some characters that are not formatting to hex properly. They are not being interpreted correctly by the strongly typed Format. For instance, consider the format string: const char x = '$'; // also, '_', for instance const auto s = (boost::format("\\x%1$02x") % x).str(); I would expect this to encode to: "\\x24", however, instead this encodes to "\\x0$". I would expect '_' to encode: "\\x5f", however, this encodes to "\\x0_". In a few words, the encoding is "seeing" the char as a literal char instead of as an "integer". Although I could possibly trap for this as being the case, I do not think that I should. Thoughts? Format authors? Best regards, Michael Powell

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Warnings from 1.69.0
by tim＠raisedbar.net 22 Jan '19

22 Jan '19

Hi, Whilst building my application using Visual Studio 2017 I get the following warnings that I wasn't getting prior to changing to 1.69.0: 1>c:\program files\boost\boost\pending\integer_log2.hpp(7): note: This header is deprecated. Use <boost/integer/integer_log2.hpp> instead. The identified header is not referenced in my own code, but is being included by the Boost logging code. Can anybody advise me as to my best way of dealing with this situation, please, as I'm trying for a warning-free build. Best wishes. Tim Burgess Raised Bar Ltd. E: <mailto:tim@raisedbar.net> tim(a)raisedbar.net M: +44 (0)7989 486976

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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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