August 2003 - Boost-users - lists.preview.boost.org

boost::shared_ptr and stl algorithms
by Bill Eidson 15 Apr '05

15 Apr '05

std::vector< boost::shared_ptr<T> > TVec; I want to write a function object to run std::for_each. to do somework against members of T and accumulate results in functor. My attempts have failed in VC7 with memory errors in my operator() method. struct fo { bool operator()( boost::shared_ptr<T>& t ) { return true; } }; Thanks in advance bille

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BGL and reversing / moving edges
by joshrose 17 Dec '03

17 Dec '03

G'day, I was hoping someone might be able to tell me if they've run into any situations using BGL where they needed to move (or reverse (i.e. flip the source and target)) an edge within a graph implemented as an adjacency_list. I'm working on an implementation of an algorithm for max. weight bipartite matching ("the assignment problem"), and one of the assumptions in the algorithm is that non-matched edges are directed from one subgraph, A, to the other subgraph, B, and matched edges are directed the other way. Over the course of growing the matching, a simple way to add and remove edges from the candidate set is just to reverse the edge, thus the need for some way to reverse the edge within BGL. I don't think I can just remove and then re-add the edge in the other direction, primarily because doing so will (I believe) invalidate any edge_descriptors referring to that edge. In particular, there are property maps keeping track of the weight of edges, the predecessors of certain nodes, etc. that use edge descriptors as keys. I've spent a fair bit of time reading the documentation and looking through the implementation of adjacency_lists (incl. edge_list_impl), and I'm not really sure of a way to either move an edge directly within a graph, or even to create a new edge from another s.t. they have the same edge_descriptor (in general a bad thing, probably). Anyone have any thoughts on this? Thanks, -Josh

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Bug in boost::format with 0 valued integer
by Simon Clift 15 Sep '03

15 Sep '03

Hi folks, There appears to be a bug in boost::format, an unitialized value problem spotted when I was using valgrind on a program of mine. The following test code illustrates the (admittedly minor?) problem: #include <boost/format.hpp> #include <iostream> using namespace std; int main() { int dummy = 5; cout << boost::format( "%05d" ) % dummy << endl; dummy = 0; cout << boost::format( "%05d" ) % dummy << endl; }; I compiled this with -g and when run with valgrind it seems that the put_last function in feed_args.hpp sends an uninitialized value into the standard library <<(int) operator when the integer to be printed is 0 and leading zeros are specified. Valgrind reports (clipped for size) on the second ::format call (but not the first) of the test code: ==28879== Conditional jump or move depends on uninitialised value(s) ==28879== at 0x40289470: (within /usr/lib/libstdc++.so.5.0.3) ... ==28879== by 0x4028F36B: std::ostream::operator<<(int) (in /usr/lib/libstdc++.so.5.0.3) ==28879== by 0x804CF8D: void boost::io::detail::(anonymous namespace)::put_last<char, std::char_traits<char>, int>(std::basic_ostream<char, std::char_traits<char> >&, int&) (feed_args.hpp:114) ==28879== by 0x804C9A2: _ZN5boost2io6detail31_GLOBAL__N_test00Fill.cppfx7Zjb3putIcSt11char_traitsIcERiEEvT1_RKNS1_11format_itemIT_T0_EERSbIS9_SA_SaIS9_EERSt19basic_ostringstreamIS9_SA_SE_E (feed_args.hpp:176) ==28879== by 0x804BF44: void boost::io::detail::distribute<char, std::char_traits<char>, int&>(boost::basic_format<char, std::char_traits<char> >&, int&) (feed_args.hpp:237) ==28879== by 0x804ABB6: _ZN5boost2io6detail4feedIcSt11char_traitsIcERiEERNS_12basic_formatIT_T0_EESA_T1_ (feed_args.hpp:246) ==28879== by 0x804A14B: boost::basic_format<char, std::char_traits<char> >& boost::basic_format<char, std::char_traits<char> >::operator%<int>(int&) (format_class.hpp:69) ... Hope this helps. Otherwise I'm enjoying using boost! Best regards --- Simon -- Simon Clift E-mail: ssclift at math dot uwaterloo dot ca Ph.D. Student Scientific Computation Group University of Waterloo Waterloo, Ontario, Canada N2L 3G1

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how to create fixtures in unit test framework
by Anders Moe 03 Sep '03

03 Sep '03

Hi all. The boost unit test framework seems to lack the xUnit buildUp/tearDown (whatever) methods meant to faciliate the creation of fixtures. Does that mean there is an alternative idiom to achieve the same effect ? Constructing new class-test-cases for each test seems a bit overkill. Regards, Anders.

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spirit list_p example
by Larry 02 Sep '03

02 Sep '03

From boost-1.30.2 I built the list_parser.cpp example using MSVC++7.1. In the CSV list I added ",,2" to the end of the line to be parsed. The program ran but the neither of the added elements were included in the output vector. Having used the tokenizer before I know it will generally gobble up adjacent delimiters without any output. You can get the empty token if you ask for the delimiters as well and then just discard the delimiters (sort of). But I was surprised that the 2 didn't make it to the output vector. I expected the empty list entry would not make the output vector. I tried adding ~anychar_p to the rule but that didn't help. If I change the input list to add ",\"\",2" I get "" and 2 in the output vector. Applications like spreadsheets do not put missing column values for numeric columns as "" items generally. Maybe I am missing something because it certainly isn't the behavior I would expect (either from the parser or the tokenizer).

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[BGL] Installing a property
by sashan 31 Aug '03

31 Aug '03

Hi I have a mass spring system where the particles are mapped to the vertex name property of the vertex. Now I've read (in the BGL red book) that one can install a custom property using an enumerated type. However it says that the enum must be a unique number. How do I enforce this in my code? Do I have to manually track the numbers myself? Thanks sashan [Non-text portions of this message have been removed]

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Given std::map<ID,struct>, efficient way to access std::vector<struct.member>?
by Chris Russell 31 Aug '03

31 Aug '03

Hello folks, I've got an interesting little design problem and I'm looking for some advice on how best to implement an efficient solution. [ I posted this message to comp.lang.c++.moderated yesterday. I'm reposting here because this _seems_ like a job for some type of iterator adaptor and I'm thinking that perhaps one of the Boost libraries might be useful in this context. But which (if any)? Would uBLAS help me here perhaps? Or am I way off base? ] Here's a simplified statement of the problem that I believe outlines the relevant details: I've got a class declared as follows: --- begin example class ---- class CFilter { public: typedef struct tag_sRow { A_t A; B_t B; C_t C; .. .. .. // some number of structure members... } sRow_t; typedef std::map<key_t/*type unimportant*/, sDataRow_t> mapData_t; typedef mapDataSet_t::iterator mapiterData_t; typedef mapDataSet_t::const_iterator mapconstiterData_t; private: mapData_t m_mapData; public: void ProcessRow(const sRow_t& sRow) { // process a single row of data } // end method ProcessRow void ProcessData(const mapData_t& mapData) { // algorithm needs fast access to: // std::vector<A_t>, std::vector<B_t>, std::vector<C_t> .... } // end method ProcessData }; // end class declaration CFilter --- end example class --- In English: CFilter declares some structure with some number of data members of arbitrary types. Internally CFilter allocates a std::map of these structures using some key_t. Effectively this defines a table of data whose rows are of type sRow_t, and whose columns can be conceptualized as std::vector<A_t>, std::vector<B_t> where std::vector<sRow_t.some_member>.size() == mapData<key_t, sDataRow_t>.size(). At runtime, CFilter.ProcessRow is called std::map<key_t, sRow_t>.size() times followed by a single call to CFilter.ProcessData. I'm trying to figure out how to _efficiently_ access the column vectors in the implementation of CFilter.ProcessData. Any suggestions would be greatly appreciated. Thanks in advance - Chris Russell

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Inconvenience in time_parsing.hpp - uninit variables
by Larry Knain 30 Aug '03

30 Aug '03

I was trying to use the date_time ptime functions with ISO syle input (boost 1.30.2 with MSVC++6 SP5). The function parse_undelimited_time_duration in time_parsing has three short variables hours, min, and sec that are uninitialized which lead to unpredictable results. These are at line 99. I stumbled on to this when I passed a string "20011027T0202" to ptime(from_iso_string()). To my surprise when I printed the value out it came back as 20011026T222345! The code works OK as is if you always pass a full HHMMSS. This must have been found in parse_delimited_time_duration as it has unsigned shorts that are intialized to zero.

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[BGL] adjancency iterators for property types
by sashan 30 Aug '03

30 Aug '03

Hi Is there an adjancency iterator for property types. You can get an iterator for property types like this: typedef graph_property_iter_range<GraphType, vertex_name_t>::iterator VNameIterator; .... tie(It, ItEnd) = get_property_iter_range(m_Graph, vertex_name); I'd like to know if there is something similar for adjacency iterators. Thanks -- sashan http://www.cs.auckland.ac.nz/~sgov008/

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boost::function syntax
by shyamemani 29 Aug '03

29 Aug '03

Hello everyone, I was looking at the boost::function preferable syntax. boost::funcion<float (int,int) > I also see that this has also been accepted by the standard for future STL implementation. The C++ grammar for template declaration is as stated below: template-argument-list: template-argument template-argument-list , template-argument template-argument: assignment-expression type-id id-expression None of the 'declaration' rules also seem to parse the tokens 'float (int,int) (I know I am missing something here). I could not figure out why the string 'float (int,int)' is accepted by the compiler and what type it is assigned? Is it just a extension of the standard by GCC? Can somebody help me figure this out? Thanks, Shyam

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