January 2012 - Boost-users - lists.preview.boost.org

problems with C++ integer types
by Robert Ramey 01 Feb '12

01 Feb '12

I'm very confused about a number of things related to C++ standard and boost libraries dealing with numeric types. Here are a few things that I'm not getting. a) The standard says in section 18.3.2.1 "Specializations shall be provided for each arithmetic type, both floating point and integer, including bool. The member is_specialized shall be true for all such specializations of numeric_limits." ... "Non-arithmetic standard types, such as complex<T> (26.4.2), shall not have specializations." and it section 18.3.2.4 numeric_limits members static constexpr bool is_bounded; "True if the set of values representable by the type is finite. [ Note: All built-in types are bounded. This member would be false for arbitrary precision types.-end note ]" So the question is: if one makes a "numeric type" like std::complex (or safe integer which I'm interested in right now). Should one define a specialization for this new type? The working is pretty specific, but then I can't see why "is_bounded" is in there since all built-in arithmetic types are bounded. Oh I see this now: Required by LIA-1. b) boost/type_traits/is_integral.hpp This file just specializes each arithmetic type supported by the implementation. question:Why isn't it just implemented in terms of numeric limits so that every thing is always consistent and never "out of sync" It's implementation returns true for only the built in types so it seems to me it should be repeating what ever happens to already be in numeric_types. c) my real interest is to implement a type "safe_integer" which can be used anywhere an integer is used but will trap errors which occur in the course of implicit conversions and assignements. If I don't specialize numeric_limits for my new "safe_integer" certain type_traits like is_signed won't work for it. If I do - them I"m out of sync with is_integral.hpp and likely out of conformance with the standard - though I'm not sure what the implications of that might be. I'm aware that there is related work going on here - bigint and arbitrary length integers. How do the authors of these libraries plan to address this. There are other cases applications where this would also come up such as modular integer<modulus> , safe_integer_range<max, min> and who know what else. Any useful information/insight would be appreciated. Robert Ramey

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Re: [Boost-users] Need help with Errors in boost MPL tutorials
by Linh Khanh ha 01 Feb '12

01 Feb '12

> There are far more than just two placeholders in Boost. AFAIK Phoenix, > Lambda and Bind come with their own. The mpl placeholder is different > though: It is a placeholder for a type (it's a meta-programming > library after all) and not for a value. Try to write a MPL lambda, > that might clear up some of the confusion. > -- Philipp Moeller, GeometryFactory That clears a lot of confusion from me. So again, mpl::lambda is also different from boost::lambda is that right (and also the lambda from c++11x) ? These are quite new terms for me. Would be great if someone could give me some references why they are different and should be implemented separately.

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Boost.Regex: Iterate over named captures/groups
by NoRulez 01 Feb '12

01 Feb '12

Hi @all, if I have a regex (e.g.: "^Subject: (Re: |Fw: )*(?<subject>.*)") I know I can access them with what["subject"] but is there a way to get a list or whatever of named captures/groups? Maybe something like the following: foreach(const std::string &str, what.namedGroups()) { std::cout << "Group Name: " << what[str] << std::endl; } Thanks in advance Best Regards NoRulez

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Boost::mpl vector product
by Allan Nielsen 01 Feb '12

01 Feb '12

Hi If I have two mpl vectors: v1 and v2 typedef boost::mpl::vector<char, short, int> v1; typedef boost::mpl::range_c<int,0,4> v2; Does boost then provide any tools for constructing the type: boost::mpl::vector< boost::mpl::pair< int_<0>, char >, boost::mpl::pair< int_<1>, char >, boost::mpl::pair< int_<2>, char >, boost::mpl::pair< int_<3>, char >, boost::mpl::pair< int_<0>, short >, boost::mpl::pair< int_<1>, short >, boost::mpl::pair< int_<2>, short >, boost::mpl::pair< int_<3>, short >, boost::mpl::pair< int_<0>, int >, boost::mpl::pair< int_<1>, int >, boost::mpl::pair< int_<2>, int >, boost::mpl::pair< int_<3>, int > > Best regards Allan W. Nielsen

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iterator: zipping and additional function
by MM 31 Jan '12

31 Jan '12

Hello, I have a list of historical datas of this form: Histodata1 Histodata2 ... Histodatan 1 Jan 1980 Data1 25 Jan 1980 Data2 2 Jan 1980 Datan 2 Jan 26 Jan 3 Jan 1980 ... 31 Dec 2004 29 dec 2004 1 dec 2004 This is implemented as class histodata { public: typedef std::vector<entry>::iterator iterator; private: std::vector<entry> data_; }; I need to obtain the union of all this data without duplicating the individual datas, so I wrote a class hisodataset { // contains a unique set of histodatas /// this contains the n datas /// Define the iterator }; The requirements of the iterator: bidirectional, but if RanAcc is possible, it would be good. . We want the union of datas, so that, if a date is present in at least 1, then the it should be present in the union. For those histodatas that don't have the date, it should simply duplicate the last available date for that histodata. . begin() on the set will return the earliest date available for all histodatas .end () will return the "one-after-last" last being the last date available in all histodatas. I'm not quite sure how to implement such an iterator. boost::zip_iterator over the underlying histodatas, but how to add to that the union part? only a const version of this union iterator is required, no writing needed. MM

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[random] saving state of generator
by Thomas Mang 31 Jan '12

31 Jan '12

Hi, Consider an application intended to run for weeks and where a deterministic sequence of random numbers is needed (deterministic in order to make results 100% reproduceable). For hardware-related reasons that application might get halted (killed). In order to smoothly restart the application I would like to regularly save the complete system state and can hence use that as restore point. That complete save works for everything except the random number generator - I am using boost::random::mt19937. The mt199937 class does not seem to offer such an option (full state save). Using serialization also does not sound great in my eyes as I am, of course, not familiar with the internal representation of mt19937. So what is the best option? Dissecting mt19937 (intrusive changes to class template mersenne_twister_engine) and making my own serialization routine? Any other / more straightforward ideas? thanks Thomas

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dijkstra-example.cpp
by fergie 31 Jan '12

31 Jan '12

I’ve been reviewing the dijkstra-example.cpp that is provided as part of boost Graph. I think I understand most of it and have been able to demonstrate the application working to my boss. I have one question about the code. When output the .dot file near the end of the program the results are shaded either grey or black. What is the significance of the black and grey lines? I’ve looked through the documentation and am also confused about the source and the target since we have an iterator going through the entire graph. What defines a source and target vertex? Thanks, D -- View this message in context: http://boost.2283326.n4.nabble.com/dijkstra-example-cpp-tp4334386p4334386.h… Sent from the Boost - Users mailing list archive at Nabble.com.

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MPL newbie : what is the difference between mpl::true_ and true_type
by Linh Ha 31 Jan '12

31 Jan '12

I'm a newbie for both boost and MPL. My question is regarding about the differences between mpl::true_ and true_type. While from my point of view they are both structure of constant boolean. Even in the implementation true_type is derived from mpl:true_. So why we need both data structure instead of only single one. When we should use mpl::true_ instead and true_type and vice versa Thanks

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ASIO: HTTP Client Issues with \r vs \n
by Fitzsimmons, Bo CIV SPAWARSYSCEN-PACIFIC, 81320 31 Jan '12

31 Jan '12

Hello, I'm trying to use the HTTP client example code (sync_cleint.cpp) to retrieve a jpg. I'm using VS2008 on a Windows XP machine and trying to access a Linux server. The resulting data I get back does not start the new lines at the same place as data I retrieve by simply downloading. I believe this is an issue with how windows interprets a new line, \r\n, versus how unix/linux interprets a new line, \n. The example code (http://www.boost.org/doc/libs/1_48_0/doc/html/boost_asio/example/http/clien…) uses \r\n, \n, and \r, so I'm a little confused on how to rectify the problem. Any suggestions to correct this for my case (hard code) or automatically detect would be greatly appreciated. P.S. I'm using boost 1.48.0 Thank you, Bo

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Raw sockets for Layer 2 communications
by Carlos Guimarães 31 Jan '12

31 Jan '12

Hi, I've been looking for any way to send L2 messages (with no transport protocol) using Boost. As long as I could find, Boost libraries support raw sockets, however it must have a transport protocol (like IP) associated. Is this right?There is any way to send a pure L2 packet? Best regards, Carlos Guimarães

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