March 2007 - Boost-users - lists.preview.boost.org

Re: [Boost-users] boost::ref and boost:::function
by Ovanes Markarian 12 Mar '07

12 Mar '07

On Mon, March 12, 2007 15:44, Peter Dimov wrote: > Misiu wrote: >> Ovanes Markarian napisaÅ(a): >>> [...] >>> >>> You could also skip the compare_functions implementation and use >>> boost::lambda and placeholder library to write you code like this: >>> std::find_if(fun_list.begin(), fun_list.end(), _1==fun); >> >> When I tried this solution (really nice one) on MSVC 2003 I got this >> error: >> >> d:\boost_ref_test\main.cpp(18): error C2666: 'boost::operator`=='' : 4 >> overloads have similar conversions > > You can't compare two function<> objects with ==. What you can do is compare > a function<> with the actual contents. That is, My appologies. I wrote this without double checking the doc. Thought it would work, since I remembered that there was a comparison operator. With Kind Regards, Ovanes Markarian

1 0

[lamba] boost::lambda::function_adaptor<Func>::apply means what?
by Boris 12 Mar '07

12 Mar '07

struct sample { int i; sample(int i) : i(i) { } bool odd() { return i % 2; } }; template <class T, class U> std::basic_ostream<T, U> &operator<<(std::basic_ostream<T, U>& ostr, sample s) { return ostr << s.i; } std::vector<sample> from; std::vector<sample> to; from.push_back(sample(1)); from.push_back(sample(2)); from.push_back(sample(3)); std::for_each(from.begin(), from.end(), if_then(bind(&sample::odd, _1) == false, bind(&std::vector<sample>::push_back, to, _1))); VC++ 8 displays dozens of error messages with the first one: error C2665: 'boost::lambda::function_adaptor<Func>::apply' : none of the 2 overloads could convert all the argument types Can anyone tell me how I need to change the lambda expression? Thanks, Boris

1 1

Andy Little's Physical Quantities System
by Polder, Matthew J 12 Mar '07

12 Mar '07

Hi, does anyone know where I can get a copy of Andy Little's Physical Quantities System? I know it wasn't accepted, but I think it would be useful for a project I'm working on. It's no longer in the Boost File Vault and I can't find it via Google. thanks, matthew

2 1

[date_time] iso time with local time differential
by Mojmir Svoboda 12 Mar '07

12 Mar '07

hello, i have simple task: convert iso time 20051108095122.5+0500 to seconds from 1900/01/01 00:00 UTC the thing is that doing something like: ... stringstream ss; local_time_input_facet * input_facet = new local_time_input_facet(); input_facet->format(local_time_facet::iso_time_format_specifier); ss.imbue(locale(ss.getloc(), input_facet)); ss << "20051108095122.5+0500"; local_date_time my_date(not_a_date_time); ss >> my_date; ... seems to drop the +-hhmm specifier and sets the zone to Z automatically in my_date. otherwise it seems to be parsed correctly. what am i doing wrong, please? mojmir This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender. Thank you.

1 0

[Serialization, XML] Suppress generation of class_id, tracking_level and version?
by Gerrit Brehmer 12 Mar '07

12 Mar '07

Hi, is it possible to suppress the in the xml-output generated attributes for object types (class_id, tracking_level and version)? Because it is better human writable/editable and in my case i have tested the reading of files w/o these attributes and it was all successful. Thanks in advance for your help!

3 2

[Threads] Conditions and avoiding lengthy mutex locks (background loading for a game)
by Peter Mackay 11 Mar '07

11 Mar '07

Hello, I'm trying to use the Boost Threads library to help me implement a background loading system for a game I'm writing. I want to enqueue load requests while the main game thread is running, and have a separate thread load the data and pass back the appropriate objects. Currently when I enqueue a new request, I notify a 'something to do' condition, which my loading thread waits on. The trouble is, when I notify it, the loader could be loading in the background, and has a lock on the mutex connected with the condition. Would anyone be able to offer me any advice on how to solve this? Many thanks, Peter P.S. Please find attached my current implementation. begin 666 loader.cpp M(VEN8VQU9&4@(FQO861E<BYH<' B#0H-"B-I;F-L=61E(#QB;V]S="]B:6YD M+FAP<#X-"@T*;&]A9&5R.CIL;V%D97(H*0T*.B!T:')E861?<VAO=6QD7V5X M:70H9F%L<V4I#0I[#0H)=&AR96%D+G)E<V5T*&YE=R!B;V]S=#HZ=&AR96%D M*&)O;W-T.CIB:6YD*"9L;V%D97(Z.G1H<F5A9%]P<F]C+"!T:&ES*2DI.PT* M?0T*#0IL;V%D97(Z.GYL;V%D97(H*0T*>PT*"2\O(%-I9VYA;"!T:&4@=&AR M96%D('1O(&5X:70N#0H)>PT*"0EB;V]S=#HZ;75T97(a)Z.G-C;W!E9%]L;V-K M(&QO8VLH;75T97(a)I.PT*"0ET:')E861?<VAO=6QD7V5X:70@/2!T<G5E.PT* M"0ES;VUE=&AI;F=?=&]?9&\N;F]T:69Y7V%L;"@I.PT*"7T-"@T*"2\O(%=A M:70@9F]R('1H92!T:')E860@=&\@97AI="X-"@ET:')E860M/FIO:6XH*3L- M"GT-"@T*=F]I9"!L;V%D97(Z.G1H<F5A9%]P<F]C*"D-"GL-"@DO+R!792=R M92!L;V-K960@=6YL97-S('=E)W)E('=A:71I;F<@9F]R('-O;65T:&EN9R!T M;R!D;RX-"@EB;V]S=#HZ;75T97@Z.G-C;W!E9%]L;V-K(&QO8VLH;75T97@I M.PT*#0H)+R\@4G5N('5N=&EL('=E)W)E('1O;&0@=&\@97AI="XN+@T*"69O M<B H.SLI#0H)>PT*"0DO+R!786ET('5N=&EL('=E(&=E="!S;VUE=&AI;F<@ M=&\@9&\N#0H)"7-O;65T:&EN9U]T;U]D;RYW86ET*&QO8VLI.PT*#0H)"2\O M(%-H;W5L9"!W92!E>&ET/PT*"0EI9B H=&AR96%D7W-H;W5L9%]E>&ET*0T* M"0E[#0H)"0DO+R!%>&ET('1H92!T:')E860N#0H)"0ER971U<FX[#0H)"7T- M"@T*"0DO+R!T;V1O.B!$;R!A;&P@<&5N9&EN9R!L;V%D<R!H97)E("AC;W5L C9"!B92!A(&QE;F=T:'D@;W!E<F%T:6]N*2X-"@E]#0I]#0H` ` end begin 666 loader.hpp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`` ` end

4 6

[graph] edmund_karp_max_flow vs kolmogorov_max_flow color map
by François Duranleau 11 Mar '07

11 Mar '07

Hi! It seems there is an inconsistency (to me) between color tagging of vertices in edmund_karp_max_flow and kolmogorov_max_flow algorithms. In the documentation of kolmogorov_max_flow, it says: "If the color of a vertex after running the algorithm is white the vertex belongs to the source tree else it belongs to the sink-tree (used for minimum cuts)." In short, vertices linked to the source are white. However, for edmund_karp_max_flow, it says: "At the end of the algorithm, the white vertices define the minimum cut set." Thus in this case, it's the vertices connected to the sink that are white. Why the difference in color tagging between the two algorithms? -- FranÃ§ois Duranleau LIGUM, UniversitÃ© de MontrÃ©al

2 5

equals() from boost/algorithm/string.hpp in top namespace?
by Olaf van der Spek 10 Mar '07

10 Mar '07

Hi, Why is equals() in the top namespace in 1.33.1? #include <boost/algorithm/string.hpp> #include <boost/array.hpp> int main() { boost::array<char, 4> a = { 1, 2, 3, 4 }; equals(a, a); return 0; }

3 3

[Serialization] How to restore ref-counted strings
by Bill Lear 10 Mar '07

10 Mar '07

We have a massive amount of data to serialize, on the order of several gigabytes. Lots of strings involved, maybe hundreds of millions. We discovered that the data structure in memory would bloat enormously when read back in from disk (say, from 2 gig to 3.1 gig). We think we have tracked this down to (gcc implementation) string reference counts not being "restored". I think a solution for us is to do something like the following: static map<string, bool> string_map; template <class Archive> void read_string(Archive ar, string& a_string) { string s; ar >> s; // read from disk map<string, bool>::iterator i = string_map.find(s); if (i == string_map.end()) { i = string_map.insert(make_pair(s, true)); } a_string = i->first; } void destroy_map() { string_map.clear(); } Then, when the data structures have all been read, invoke the destroy_map() method to clear the string_map object, thus decremented all refcounts of strings by one. Has anyone else encountered this and found a solution? Also, if anyone has bright ideas on a better data structure than std::map to use for storing hundreds of millions of strings at once for the above purpose, that also might be nice. Thanks. Bill

2 8

[MPL?] generating functions for all fields in a struct
by Christoph Duelli 10 Mar '07

10 Mar '07

Given a struct like struct X { int a; char b; float c; } and some function-'template' f is it possible to 'generate' - preferably by means of templates, MPL or something of the kind - variations of some function f for each of X's fields? E.g. I'd like to have functions like int getA() { return a; } char getB() { return b; } float getC() { return c; } ... (The functions I have in mind are more complex, obviously, but the idea is to generate one such function for all the fields of X.) I would like to avoid writing a macro call or something per field, as I would like the code to work (after recompiling it) even if the definition of X is changed and some fields are added. So, is there some generic 'iterator' over the fields of a struct? Thank you and best regards Christoph

4 4