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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 30 Aug '03

30 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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Broken link on boost.org/libs page
by Sam Partington 29 Aug '03

29 Aug '03

http://www.boost.org/libs/hdr_depend.html Is giving a HTTP 404 error. Cheers Sam

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Re: Lambda shortcut?
by Daryle Walker 27 Aug '03

27 Aug '03

On Tuesday, August 26, 2003, at 10:05 AM, Jaakko Jarvi wrote: > In our last exciting episode Stephen Love wrote: >> operator-> *is* overloadable. > > It is, but not freely. The return type cannot be arbitrary, say a > lambda_functor type, making it not very useful for the LL. Specifically, the right side of "->" must be the NAME of a class' member or member function. It cannot be any kind of actual object (including pointers-to-member). This restricts the left side to: 1. A pointer to a (class/struct/union) data object (conventional C usage) 2. A class object with an "operator ->()" that returns a pointer to a data object 3. A class object with an "operator ->()" that returns an object that follows rules [2] or [3]. No matter what, "operator ->()" eventually leads to the standard C usage. All you can do is delay the event and build proxy objects to obtain the data. Daryle

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Link errors
by Ken Crismon 26 Aug '03

26 Aug '03

To all, I am a new user to the BOOST community and am putting together some test code to get a handle on what BOOST is and how it works. Am using .NET 2003 and am getting the following link errors. error LNK2019: unresolved external symbol "__declspec(dllimport) public: class std::_Ptrit<char,int,char *,char &,char *,char &> __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::end(void)" Thanks in advance for the help, Ken Crismon

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First Boost installation under Windows and Borland
by Matías Nicolás Bossa 26 Aug '03

26 Aug '03

Hello, I'm a new Boost user and I need to install it (v. 1.30.0) under Windows 2000, with Borland C++ Builder 6. I've succeed in correctly installing and using it under linux, but I couldn't install it under Windows. I downloaded and unpacked boost_1_30_0.zip. I set the following variables: BOOST_ROOT=d:\proyect\boost_1_30_0 TOOLS=borland BCCROOT=c:\archiv~1\borland\cbuilder6 PYTHON_ROOT=c:\win\python I compiled bjam.exe by running tools\build\jam_scr\build.bat, and put it somewhere in the path. (but I also tried downloading a precompiled version) I run bjam from the boost_1_30_0 directory and the following message appeared: /****************************************************/ /****************************************************/ ...found 5339 targets... ...updating 573 targets... borland-C++-action libs\python\build\bin\boost_python.dll\borland\debug\runtime-link-dynamic\numeric.obj libs\python\build\../src\numeric.cpp: Error E2401 D:\project\boost_1_30_0\boost/python/object/inheritance.hpp 69: Invalid template argument list Error E2040 D:\project\boost_1_30_0\boost/python/object/inheritance.hpp 69: Declaration terminated incorrectly Error E2231 D:\project\boost_1_30_0\boost/python/object/inheritance.hpp 130: Member cast_generator<Source,Target>::is_upcast cannot be used without an object Error E2401 D:\project\boost_1_30_0\boost/python/object/inheritance.hpp 131: Invalid template argument list Error E2040 D:\project\boost_1_30_0\boost/python/object/inheritance.hpp 132: Declaration terminated incorrectly Error E2228 D:\project\boost_1_30_0\boost/python/object/inheritance.hpp 132: Too many error or warning messages *** 6 errors in Compile *** /****************************************************/ /****************************************************/ For the moment I just need ublas and random libraries, I need boost in order to compile another library which use it, called Bayes++. I wil be very grateful if someone could help me, and I'm sorry for the length of the mail. Regards, Matías ___________________________________________________ Yahoo! Messenger - Nueva versión GRATIS Super Webcam, voz, caritas animadas, y más... http://messenger.yahoo.es

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Lambda shortcut?
by Hurd, Matthew 26 Aug '03

26 Aug '03

Hi, Is there a short cut for bind(&class::method_name, this, _1)? I could wrap it in a macro, as I use it enough, but is there something nicer I'm missing? I often just do the for loop as it is a little more readable, maybe... For example, for( some_collection::iterator i = check_list.begin(); i!= check_list.end(); ++i ) { turn_off_calcs(*i); } Is hopefully the same as for_each( check_list.begin(), check_list.end(), lambda::bind(&instrument_store::turn_off_calcs,this,lambda::_1) ); Regards, Matt.

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How to use boost::bind
by Darren Cook 26 Aug '03

26 Aug '03

Hi, I have a project with many occurences of while loops iterating through a container, and operating on the data. I'd like to use for_each() and turn them into one-liners, but I don't like writing one-off functor classes. I was hoping boost::bind could help, but I've read the docs, scratched my head, and failed to work out how the examples apply to my case. Maybe they don't and I'm trying to use it for something it cannot do? See an example below. My function currently looks something like grab_keys() and I want it to look like grab_keys2(). Could some kind soul show me how to write this? (or explain why it cannot be written). Thanks, Darren ------------------------- class Info{ public: int key; std::set<int> points; }; class InfoContainer{ public: Info* get(int); }; void grab_keys(const InfoContainer &cs,const Info *c){ std::set<int> list; std::set<int>::const_iterator i=c->points.begin(); while(i!=c->points.end()){ Info *ec=cs.get(*i++); list.add(ec->key); //Previous two lines could be written: list.add(cs.get(*i++)->key); } //Do something with list here. } void grab_keys2(const AllInfo &cs,const Info *c){ Points list; std::for_each(c->points.begin(),c->points.end(), boost::bind( /* what goes here? */ ) ); //Do something with list here. }

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