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Iterator nesting
by Rodrigo de Salvo Braz 20 Nov '04

20 Nov '04

Hello, Suppose I have a container of containers and would like an iterator that goes through all of their elements as if they are coming from a single container. I thought I would see some Boost class helping me to do that but I couldn't find anything like that. Can someone please tell me if that is true, and if not, which class can I use to that effect? (In fact this concept is more general and interesting. The objects in the first-level containers may not be containers but have members which are containers and whose elements I want to iterate through. Or they could be iterators. The general case should allow a parameterizable way of obtaining an iterator to the elements inside the second-level objects. This could again be a nesting iterator, allowing for arbitraty nesting. Since this is a fairly common need in programming, I was expecting something that did that in Boost.) Thanks, Rodrigo

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Another weird boost::variant problem.
by Bo Peng 19 Nov '04

19 Nov '04

Dear list, I have a problem with apply_visitor of boost::variant. It seems to me that it can not accept a temporary variant variable that is returned from a function. Is this a bug? Here is a simple example: =================================== #include "boost/variant.hpp" using namespace std; #include <string> typedef boost::variant<double, string > Variable; #include <iostream> // a simple visitor that returns a variant. class variantPlusOne : public boost::static_visitor<Variable> { public: Variable operator()( double i) const { return Variable( i + 1 ); } Variable operator()( string str) const { return Variable( 0); } }; // apply_visitor in function form Variable func(Variable a) { return boost::apply_visitor( variantPlusOne(), a); } // a silly function. Variable me(Variable a) { return a; } int main() { Variable b("5"); cout << func(b) << endl; // OK cout << func(me(b)) << endl; // OK cout << boost::apply_visitor(variantPlusOne(), b ) << endl; // OK // cout << boost::apply_visitor(variantPlusOne(), me(b) ) << endl; // NO return 0; } ///////////////////////////// The error messages are: test.cpp:44: no matching function for call to `apply_visitor(variantPlusOne, Variable)' boost_1_31_0/boost/variant/detail/apply_visitor_unary.hpp:59: candidates are: Visitor::result_type boost::apply_visitor(Visitor&, Visitable&) [with Visitor = variantPlusOne, Visitable = Variable] boost_1_31_0/boost/variant/detail/apply_visitor_unary.hpp:75: Visitor::result_type boost::apply_visitor(const Visitor&, Visitable&) [with Visitor = variantPlusOne, Visitable = Variable] /////////////////////////////// Note that I can understand this behavior if the visitor takes reference arguments (and therefore expects a persistent variable) but my visitor pass argument by values. Thanks. Bo

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boost::filesystem::path - where are the attributes?
by Pete 19 Nov '04

19 Nov '04

I'm not sure if I'm missing something or not, but I couldn't find anything in the filesystem documentation that allows one to retrieve file/directory attributes such as: Date created/last accessed/last modified Hidden System Read Only Link Etc. I'm particularly interested in portable file date accessors (hoping to find methods in the path class returning boost::posix_time::ptime). Are there any known workarounds?

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function_traits of bind - functors possible?
by Roland Schwarz 19 Nov '04

19 Nov '04

Is it possible to use function_traits for functors that have been created with bind? I.e.: template<Function> foo (Function f) { typedef typename boost::function_traits<Function>::type fn_t; boost::signal<fn_t> sig; } .... foo(boost::bind(fobar, this, _1)); Apparently the above does not work, but I cannot figure out what I am missing. Roland

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FW: Leak when using boost threads under VC .NET using statically linked CRT
by alansa＠ati-uk.com 19 Nov '04

19 Nov '04

The following code leaks memory for each iteration of the loop for (;;) { boost::thread t(func); t.join(); } void func() { cout << "------" << endl; } If I replace func with func2 void func2() { try { throw 1; } catch {} } then it still leaks. But if I say fill up a vector with stuff or just return there is no leek. The interesting part is that it doesn't leak if use the version of threads built using the CRT as a .dll rather than static link. I also believe that the actual culprit is somewhere in boost.function since the code for boost.thread is so straight forward. I'm currently using boost 1.30 so it might have already been addressed in newer versions. Can anyone help?

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Signals & Slots
by Foster, Gareth 19 Nov '04

19 Nov '04

I think if you just follow through the different typical tasks you might undertake with the two libraries as Murray wrote: " 1. Create a signal 2. Connect a slot (callback function) to a signal. 2.2 For a member method. 2.3 For a non-member or static function. 3. Disconnect a slot. 4. Bind an extra parameter, so that e.g. a slot with 4 parameters can be used with a signal with 3 parameters. I don't personally find the more complex adaptors interesting. " Then write up a document where, in each case, the code needed for both libraries is given, and then I small discusion about any differences or similarities. Perhaps in each case, giving some approximate figure to indicate the similarity would be useful. Presumably, this could then end up in the appendix of, or being referenced by, a proposal for a standard signals/slots interface. I don't know what is involved to be honest. I suppose, it needn't be just the one person doing the comparison, there are four tasks in the list (and maybe a few more besides), so four people could spread the work load, and maybe a 5th could add final conclusions and draw together the others notes. Cheers all, Gaz -----Original Message----- From: libsigc-list-bounces(a)gnome.org [mailto:libsigc-list-bounces@gnome.org] On Behalf Of Carl Nygard Sent: 18 November 2004 19:20 To: Doug Gregor Cc: libsigc-list(a)gnome.org; boost-users(a)lists.boost.org; gtkmm-list(a)gnome.org Subject: Re: [sigc] Re: [Boost-users] Signals & Slots On Thu, 2004-11-18 at 14:09, Doug Gregor wrote: > On Nov 18, 2004, at 1:10 PM, Murray Cumming wrote: > I'm not in a position to do this at the moment, although possibly in > the future. It would be *wonderful* if someone went off and studied > both libraries in-depth to make this comparison, especially if that > person was not intimately familiar with either library beforehand. I'm in a reasonably sane position to do this, although only time will tell if what comes out is useful to anyone or not. Regards, Carl _______________________________________________ libsigc-list mailing list libsigc-list(a)gnome.org http://mail.gnome.org/mailman/listinfo/libsigc-list

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SV: [Boost-users] Manual in pdf?
by Daniel Lidström 19 Nov '04

19 Nov '04

) ) Daniel Lidström writes: ) > Hi, ) > ) > is the manual available in pdf or postscript? Or is there a way ) > to print it? The online manual is not very printer-friendly. ) ) Daniel, ) ) I assume you are talking about Boost-wide PDF (some of the Boost ) libraries/tools provide a standalone one on their own). In that case, ) it's not available for 1.31; we are working on making it available in ) the upcoming 1.32.0, which is due in a couple of days. ) How about the Spirit manual? Will it be available in printable format with 1.32.0? Thanks! -- Daniel

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Spirit help (again)
by Cory Nelson 19 Nov '04

19 Nov '04

Okay, I'm trying to learn Spirit and I've got the grammar down. I've tried looking at the documentation but still can not find out how to make a custom parser (that will let me use the [action] operator). Could someone give an example of a pascal string parser (one byte for length, string follows) to get me started? -- Cory Nelson http://www.int64.org

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MPL Library
by Edward Diener 18 Nov '04

18 Nov '04

I have bit the bullet and am attempting to get my head around the MPL library. I realize there is a book out by Messieurs Abrahams and Gurtovoy, I believe, but I thought I would tackle the boost documentation first. A few questions: 1) Is the documentation up to date ? 2) There are three separate documents to study, it seems, all giving information about the MPL library, a white paper circa 2002, a reference, and a mini-tutorial. Is the information in these in sync with each other ? The reason I ask is that the white paper/mini-tutorial mentions if_<> and apply_if<> but the reference does not mention them at all.Are they just understood intrinsic metafunctions that need no reference, or what ? If the former, are there more of these intrinsic metafunctions and, if co, what are they and what do they do ? 3) A number of the topics in the reference documentation mentioned in generalized overviews of the various sections have no specific links. Does this mean that they were never implemented ? Seems dubious in a number of cases. I would seriously like to figure out how MPL works and play around with it, but I feel stymied with what is in the boost docs.

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Key iterators
by Chris Goller 18 Nov '04

18 Nov '04

I'm just getting into boost and I really like it. I would like to iterate over keys of a multimap. so it would look like this: std::multimap<type, type>::key_iterator i = map.beginkey(); i != map.endkey(); i++ at each i++ it would move to the next key. -or- for_each(map.beginkey(), map.endkey(), whatever); Is this possible with the boost iterators? Thanks, Chris

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