June 2010 - Boost-users - lists.boost.org

boost::regex - I do not understand why this test fails.
by Mauricio Gomes 23 Jun '10

23 Jun '10

Hi, Below it is a self contained example and the output it produces. I thought I would get a match for REGEX2 but not for REGEX1 in string s. However REGEX1 matches and produces weird (for me) results. I would expect REGEX1 only matches for strings with 6 terms (3 words and 3 numbers). I know this probably is just a regex (lack of ) knowledge problem on my part and not a boost::regex problem but I could not find a better forum than this one to ask for help. Thank you in advance for your attention ! Mau. #define BOOST_TEST_MODULE test_module_example #include <boost/test/included/unit_test.hpp> #include <boost/lexical_cast.hpp> #include <boost/regex.hpp> #include <string> BOOST_AUTO_TEST_SUITE(example_suite) BOOST_AUTO_TEST_CASE(example_test) { boost::cmatch res; std::string s = " JETIX 2,957,081 643,225.51 0.00"; // tabs separating the terms. static const std::string& REGEX1 = "\\s*(\\w+)\\s+([\\d,\\.]+)\\s+([\\d,\\.]+)\\s([\\d,\\.]+)\\s*$"; static const std::string& REGEX2 = "\\s*(\\w+){1}\\s*(\\w+){1}\\s*(\\w+){1}\\s+([\\d,\\.]+){1}\\s+([\\d,\\.]+){1}\\s([\\d,\\.]+){1}\\s*$"; boost::regex rx(REGEX2); if (boost::regex_match (s.c_str(), res, rx)) { BOOST_CHECK_EQUAL ("JETIX" , res[1]); BOOST_CHECK_EQUAL ("2,957,081" , res[2]); BOOST_CHECK_EQUAL ("643,225.51", res[3]); BOOST_CHECK_EQUAL ("0.00" , res[4]); } else { BOOST_FAIL ("It was supposed to match."); } boost::cmatch res2; boost::regex rx2(REGEX1); bool match = boost::regex_match (s.c_str(), res2, rx2); for (unsigned i = 0; i < res2.size (); ++i) std::cout << res2[i] << std::endl; if (match) // IT FAILS HERE. BOOST_FAIL ("It was NOT supposed to match."); } BOOST_AUTO_TEST_SUITE_END() -------------------------------------------------------------------------------------- Output: Running 1 test case... JETIX 2,957,081 643,225.51 0.00 JET I X 2,957,081 643,225.51 0.00 C:/projects/test/main2.cpp(40): fatal error in "example_test": It was NOT supposed to match. *** 1 failure detected in test suite "test_module_example" Process returned 201 (0xC9) execution time : 0.250 s Press any key to continue.

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Re: [Boost-users] ptrdiff_t
by yushang 23 Jun '10

23 Jun '10

I've check crtdefs.h on my system . It defined ptrdiff_t here but not under std namespace . Is the right place that ptrdiff_t got defined ? If not in which file should ptrdiff_t be defined . Maybe I should search the file where size_t got defined ? thanks in advance > Message: 7 > Date: Wed, 23 Jun 2010 10:56:27 +0200 > From: Niels Dekker - address until 2010-10-10 > <niels_address_until_2010-10-10(a)xs4all.nl> > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] ptrdiff_t > Message-ID: <4C21CC3B.30408(a)xs4all.nl> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Stefan Strasser wrote: >> Zitat von yushang: >> >>> I'm using boost with VC , when using array.hpp compiler complain the >>> following error: >>> 'ptrdiff_t' : is not a member of 'std' >>> I searched ptrdiff_t definition in all files , found it defined in >>> crtdefs.h which is not in namespace std. But array class has this >> >> #include <cstddef> >> >> array should include it though, if it doesn't please file a bug report: >> http://www.boost.org/support/bugs.html > > > ptrdiff_t *is* a member of 'std'. And boost/array.hpp *does* #include > <cstddef>. At least at http://www.boost.org/doc/libs/1_43_0/boost/array.hpp > > So yushang, do you really think it's a Boost bug? > > Kind regards, > > Niels > -- > Niels Dekker > http://www.xs4all.nl/~nd/dekkerware > Scientific programmer at LKEB, Leiden University Medical Center > >

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[array] range check (at compile time)
by alfC 23 Jun '10

23 Jun '10

Hi, Lately I find myself using boost::array intesively, specially in small demo programs. Sometimes, when "manually" accessing the elements I type a index out of range. The library can detect these errors once the program is running but I found this a waste, also I was surprised not to see this kind of static check not implemented in the library. So I wanted to see if I could enforce range checking at compile time, and I come out with this solution. namespace boost{ //sorry about the namespace name template<size_t IDX, typename T, size_t N> const T& get(boost::array<T, N> const& arr){ BOOST_STATIC_ASSERT(IDX<N); return arr[IDX]; } template<size_t IDX, typename T, size_t N> T& get(boost::array<T, N>& arr){ BOOST_STATIC_ASSERT(IDX<N); return arr[IDX]; } } #include<iostream> void main(){ boost::array<double, 3> a = {1,2,3}; std::clog<<boost::get<2>(a)<<std::endl; // ok, (namespace specification needed, why?) std::clog<<boost::get<5>(a)<<std::endl; //does not compile return 0; } (I though about using enable_if instead of BOOST_STATIC_ASSERT but that would be too much overengineering.) Is this implemented already in some other way? Alfredo

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Best libraries for a Boost workshop
by José Tomás Tocino García 23 Jun '10

23 Jun '10

Hi, I'm going to be teaching a four hours workshop about getting started with Boost, and I'm wondering which libraries would be the most representative and interesting to show. I was thinking about doing a quick review of the boost libraries that were accepted for the C++ Technical Report 1, quickly saying what each is about, and showing one example. That would be the first part of the workshop. For the second part, I'm making a selection of the most interesting libraries. I'd thoroughly explain each of them, showing several examples and maybe giving some time for the students to fiddle with their computers and the libraries. And here's where I need your help. So far, the libraries I'm sure I'm going to teach are: smart pointers, lexical_cast, bind and function, ref, hash and unordered containers. I'd also add strings algorithms, maybe regex and/or tokenizer. I'm not sure about «program options». Anyway, what's your advice? What are the 12~15 boost libraries you find essential? Thanks in advance. -- José Tomás Tocino García

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[multi-index] looking for "not greater than"
by Igor R 23 Jun '10

23 Jun '10

Hello, I've got a container with an ordered non-unique key. I have to find an element, which is not greater than X. [1, 3, 3, 5, 7] myIndex.not_greater_than(4) --> 5 myIndex.not_greatet_than(7) --> 7 myIndex.not_greatet_than(8) --> 7 IUUC, neither lower_bound(), nor upper_bound() can help here. Is there a simple way to do this? Thanks.

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[BGL] Stoer–Wagner min-cut algorithm
by Daniel Trebbien 23 Jun '10

23 Jun '10

> The usual idiom for that in BGL algorithms is to use an > iterator_property_map on the graph's vertices, built using a vector and > indexed by the vertex_index property map of the graph. You can also use a > shared_array_property_map, which manages its storage internally. If you > are doing a generic algorithm, the logic to manage these maps correctly is > somewhat difficult. One place to look for a template of what to do is the > distance map handling at the bottom of > <boost/graph/dijkstra_shortest_paths.hpp>, particularly > dijkstra_shortest_paths() and detail::dijkstra_dispatch1(). The basic > logic is to look at the named parameter structure that the user passes is > and see if there is an assignment map there. If so, use it; otherwise, > look for a vertex_index map in the named parameter structure, defaulting > to get(vertex_index, g), then use the found vertex_index map to create an > iterator_property_map or shared_array_property_map. Now that compilers > are more compliant, there are probably simpler ways to implement the logic > than to use multiple dispatch functions, but the approach in > dijkstra_shortest_paths.hpp is known to work. > > When you get this algorithm done, you may want to contribute it to BGL to > be added to Boost. We are always interested in new algorithms. > > -- Jeremiah Willcock Hello Jeremiah, I would very much like to contribute my implementation of the Stoer–Wagner min-cut algorithm to BGL. In preparation for this, I have attached a "pre-release" version to this e-mail which has everything needed to build the test case with g++ and GNU Make. Before I add in all of the template code to support "default" template parameters and other niceties, I figured that it would be good to have a review of the code to make sure that I am headed in the right direction. Also, I have tested my code against the example from Stoer & Wagner (1997). It appears to be working correctly, but there might be bugs. I think that it would be good to have more testing. Would someone please review my code? Also, is anyone aware of good examples for testing min-cut implementations? Daniel

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Re: [Boost-users] boost-io streams building with zlib/bzip2 again
by Filip Konvička 23 Jun '10

23 Jun '10

Hi Sean, > Bjam toolset=msvc stage –SZLIB_SOURCE=”c:\progrma files\zlib\” > > This still doesn’t find the zlib.h file which is in c;\program files\zlib. Are you sure you don't have any typos in your path? :-) I don't know what the official way is, but I use something like this (guessing your actual zlib path): set "ZLIB_SOURCE=C:\Program Files\zlib" bjam ....... I'm not sure whether the space in the zlib path could be an issue.... Cheers, Filip

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Boost Graph - Get the vertex based on the
by Muthuveerappan Alagappan 23 Jun '10

23 Jun '10

Hi, I am a newbie to boost graph library (BGL). 1) To build a graph with vertices with unique ids - Able to do this 2) To get the vertex containing a specific idsI have created a graph with vertices that have a custom property. - how can I do this ? The way I have tried to do is to iterate through all the vertices and checked each vertex's property value. Is there a better way to do this ? Note - This field is a unique Id field Can it be indexed based on the unique id, so that it can be accessed directly ? I have attached the cpp file which shows a small example. It would be great if someone can help with this. Thanks, Muthu

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ptrdiff_t
by yushang 23 Jun '10

23 Jun '10

Hi dear all, I'm using boost with VC , when using array.hpp compiler complain the following error: 'ptrdiff_t' : is not a member of 'std' I searched ptrdiff_t definition in all files , found it defined in crtdefs.h which is not in namespace std. But array class has this declaration: typedef std::ptrdiff_t difference_type; which cause compiler's complaining , a work arround is to get rid of the std namespace typedef ptrdiff_t difference_type; but I found there are a lot of files to change , apparently this is a tough task , any good suggestion ? thanks in advance

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[iterator] lazy container
by alfC 23 Jun '10

23 Jun '10

Hi, I am implementing a lazy container/iterator that represents the results of certain iterative algorithm. I have a class (call it solver) that should look like an interator. First I was using boost.operators to make it look like a pointer but then I found boost.Iterator. Because of the nature of the algorithm it can be only traversed forward. I am using it in this way: class solver : //public boost::dereferenceable<solver, result const*>, //replaced with boost::iterator public boost::iterator_facade<solver, result const, boost::forward_traversal_tag, result const /*noref*/ >{ ... result dereference() const{ //was result operator*() const ... } void increment() {...} //was operator++ } note that tipically the last argument is intended to be a reference but in this case, since there in no underlying data the return can't be a reference but a new element generated by the algorithm. Question: is this the intended use of boost::iterator_facade is there an alternative base class for lazy operators? Thank you, Alfredo

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