February 2010 - Boost - lists.preview.boost.org

[transact] code in sandbox
by strasser＠uni-bremen.de 11 Feb '10

11 Feb '10

Hi, I haven't had much time lately, and that's not going to change to next couple of weeks, so I've uploaded what I have so far to the sandbox: https://svn.boost.org/svn/boost/sandbox/transaction/boost/transact/ what's new: *** basic_transaction_manager: - now supports all kinds of combinations of commits, like we've discussed, including one-phase/transient two-phase, persistent two-phase. no logging/recovery yet. - lazy and non-lazy transaction construction, user-configurable *** simple_transaction_manager: a transaction manager supporting only one resource. basic_tranaction_manager includes a lot of MPL/fusion and the logging infrastrucure, none of which is needed for only one resource. this is intended to be the default transaction manager when one of our libraries is used on its own. *** logging infrastructure: to be used by basic_transaction_manager for its distributed transaction log, and optionally by resource managers that need logging (so it is part of the public interface!) - olog_files: maintaining log files without knowing its contents, manual log rolling - otransaction_log_files: same as olog_files, but automatic log rolling based on transactions - olog: writes to olog_files, aware of log entries - olog_buffer: same interface as olog, but buffers log entries locally and only accesses the log when the internal buffer overflows. - TODO: ilog_files/ilog to read/recover from logs. code is there, but not migrated to "transact". - TODO: interleaved_ologs/..., providing multiple olog interfaces so different resource managers can share a log, as we've discussed. *** new syntax for transaction scopes: syntax changed from: atomic{ ... }retry; to do atomic{ }commit(); I prefer that syntax because it resembles the do{}while(...) syntax. downside is that it conflicts with transaction::commit() if the user chooses to define BOOST_TRANSACT_COMMIT to "commit" (as is done above). *** TODO object_access not migrated to "transact" yet. utility functions for resource managers to serialize/clone/compare/... objects. regards, Stefan

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Re: [boost] Iterator facade example could use some changes/documentation adjustments
by Jacob McIntosh 11 Feb '10

11 Feb '10

> From: Jeffrey Hellrung <jhellrung(a)ucla.edu> > To: boost(a)lists.boost.org > Subject: Re: [boost] Iterator facade example could use some > changes/documentation adjustments > > I think this is a valid concern, though I'm guessing this would cause > problems at most infrequently. I'm having difficulty coming up with a > use case where this would be a problem. Did you stumble upon this while > writing "real" code? It just came to mind while I was writing some of my own iterators. I wasn't even using iterator facade to do it, as I ended up using raw pointers for iterators in my use case, but I started looking at the documentation for is_convertible to figure out why they chose that conversion, and noticed the other behavior. And, though I personally haven't used that in real code, I could imagine a developer having the bright idea of converting a derived iterator into a base one thinking it will _only_ remove his need to explicitly cast the value provided by the derived iterator for whatever purpose. But, even disregarding that, on a more basic level... using is_convertible to allow conversion from non-const to const iterators is really doing more than just that. It's letting you do a host of other things as well... and though my example involved derived classes, The same would happen in cases like converting an integer iterator into a double iterator, as is_convertible returns true in that case as well. Any time the size of the types is different, it could cause problems. This is arguably a very stupid usage of iterators, but if we can enforce proper usage via compile time errors rather than runtime errors... why not? > > Would this motivate the existence of an is_iterator_convertible > metafunction, which is identical to is_convertible except for pointers? > > - Jeff > I'm not sure what there is to gain from this, would have to see what functionality is_iterator_convertible would provide. IMO, it doesn't make a whole lot of sense to convert an iterator<A> to iterator<B> unless A == const B. Converting a const iterator to non-const iterator wouldn't enforce the access of the const iterator, and doing so in a copy constructor removes the need to const_cast for clarity. And converting an iterator<derived> to iterator<base>... or iterator<int> to iterator<double> doesn't seem to make much sense, to me. - Jacob

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Iterator facade example could use some changes/documentation adjustments
by Jacob McIntosh 10 Feb '10

10 Feb '10

My example here: http://codepad.org/pH3pXAvb As mentioned in the comment block at the codepad page: http://www.boost.org/doc/libs/1_41_0/libs/iterator/doc/iterator_facade.html… The above link demonstrates in a linked-list scenario, using is_convertible to handle the conversion from non-const iterators to const iterators. This works fine in the example's linked list scenario, but it's likely than many users of iterator_facade will more generally copy this usage to their own container, from the example. However, as my example demonstrates, in the case where the data lives in contiguous memory locations, or perhaps other scenarios, using is_convertible is very bad for this purpose. It lets you convert from a derived class pointer to a base class pointer, and this is problematic if sizeof(base) is less than sizeof(derived) See the below, very minimal example to illustrate my point. Look at CFixedTest for my proposed replacement for is_convertible to prevent this undesirable behavior. Seems to me that noting such behavior, or simply changing the example code to not allow the conversion (as my example does), would remedy the misunderstanding/problem. Just thought I'd contribute that - thanks, nacitar

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[iterator] Interest in abstract iterator?
by Andrey Semashev 09 Feb '10

09 Feb '10

Hi, Quite a few times I needed a type-erased iterator, that is somewhat similar to boost::function and boost::any with regard to functors and other objects. I've crafted a simple abstract_iterator that is capable to adopt other iterators. Main features are: * A quite small and simple implementation. * Small objects optimization. By default, adopting iterators with size of a pointer or smaller will not result in dynamic memory allocation. * The abstract_iterator is capable to adopt other abstract_iterators of the same or more relaxed iterator category without increasing the adoption level. * Most operations on the iterator introduce a virtual function call overhead. Operations involving two iterators also require a dynamic_cast. The code is in the Vault: http://tinyurl.com/yhxbkl3 Tested on MSVC 9. Is there any interest?

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[1.3.9][thread]:nm: libboost_thread-gcc40-mt-1_39.sl: no symbols
by gopal haldar 09 Feb '10

09 Feb '10

Hi I have built the boost thread library locally in hpux 11.23 system. But when I try to check the symbol in the library using nm it displays the following message. nm: libboost_thread-gcc40-mt-1_39.sl: no symbols. Please let me know how to check the symbols in boost library. Regards Gopal

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[rfc] sized_array
by Tim Blechmann 09 Feb '10

09 Feb '10

hi all, i have a small class, something between std::vector and boost::array. if others find it useful, i could submit it as an extension to the boost.array libray. it basically implements a dynamically sized array, similar to boost::array, but its size can be defined at run-time, rather than compile-time. in contrary to std::vector, which is only required to support random-access iterators (which are implementation-defined), my class guaranties to allocate the data in one consecutive memory area. it can basically be used like boost::array, the only difference is its constructor, which takes either an integer size or a container. boost::array<float, 5> ba; sized_array<float> sa(5); // initialize to size 5 assert(sa.size() == ba.size()); // container size ba.assign(pi); sa.assign(pi); // assignment sized_array<float> sa2(ba); // construct from container the code is available at [1], would be interested to hear, if other people find it useful .. thanks, tim [1] http://tim.klingt.org/git?p=nova-server.git;a=blob;f=source/utilities/sized… -- tim(a)klingt.org http://tim.klingt.org Art is either a complaint or do something else John Cage quoting Jasper Johns

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[website] Move guidelines and developer documentation to Trac?
by Daniel James 09 Feb '10

09 Feb '10

Hello all, The guidelines and developer documentation on the boost site are getting a bit old, and no one's really updating them. Meanwhile new developer documentation is being written on the Trac wiki. It seems confusing to split the documentation over two sites, and most developers find it easier to update the wiki so it might be a good idea to move all the developer documentation over to the wiki and the Trac would become the 'developer's site'. This could also help improve the main boost site. It could be simpler and more focussed towards users. Some developer pages would probably have to remain on the site for technical reasons (such as test results) and some articles might not be appropriate, or we might not have the author's permission to put them on a wiki. The developer section would be replaced by a page suggesting how to contribute to boost (along the lines of http://lists.boost.org/MailArchives/boost-docs/2010/01/3960.php) We'd also keep the calendar on the main site in some form, as it can be useful for users. Any thoughts? Daniel

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TMP runtime access problem
by Willy Liu 09 Feb '10

09 Feb '10

Hi, I wonder that how to access metadata in runtime. If I pre-compute something and save them into a template ARRAY<int N>, how can I random access the metadatas in runtime? What I can only do is binary searching. Is it possible to do in constant time, or there exist some functions in MPL doing this? #include<cstdio> using namespace std; template<int N> struct ARRAY { static const int a = ARRAY<N - 1>::a * 2; }; template<> struct ARRAY<0> { static const int a = 1; }; template<int LOWER, int UPPER> struct BS { static const int MID = UPPER + LOWER >> 1; typedef BS<MID + 1, UPPER> GREATER; typedef BS<LOWER, MID> LESS; static inline int binary_search(int n) { if(n > MID) return GREATER::binary_search(n); else return LESS::binary_search(n); } }; template<int N> struct BS<N, N> { static const int MID = N; typedef ARRAY<MID> result; static inline int binary_search(int n) { return result::a; } }; int main() { int n; printf("2^n n:"); scanf("%d", &n); printf("ARRAY<%d>::a = %d\n", n, BS<0, 30>::binary_search(n)); main(); return 0; }

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[GGL][Polygon][Union] Union returns hole (inner ring) of the expected result as the output polygon (outer ring)
by Mohammad Morshed Alam Helal 09 Feb '10

09 Feb '10

Hi, Union of two polygon_2d returns a hole (inner ring) as result. Where - Input polygons - Polygon 1: A big rectangle with a hexagonal hole inside Polygon 2: A triangle that intersects the hole from inside leaving portion of it in the hole Output polygon - The hexagonal hole without the triangle-portion. Expected output polygon - The big rectangle with current output polygon as hole (inner)as described in this picture. The Union of a rectangle with a hexagonal hole and a triangle intersecting the first polygon ***************************** ***************************** ***************************** ******** ********* ******* **X***** ****** XXX***** ***** XXX****** **** XX ***** ***** ****** ****** ******* ******* ******** ******** ********* ***************************** ***************************** ***************************** returns this polygon, instead of the correct result. ++++++++++++ ++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++++++++ +++ ++++++++++++++++++ ++++++++++++++++ ++++++++++++++ ++++++++++++ You can use the code bellow to generate the case and some PPM images. You may use a WSQ Viewer to see the polygons. Please let me know any workaround or anything thats I am missing. Thank and regards, Helal // the code void uniontest() // Your main should call it { double L = 200.0; const double outloop[][2] = { {L, L}, {L, -L}, {-L, -L}, {-L, L}, {L, L} }; double R = 100.0; double H = R * sqrt(3.0) / 2; const double inloop[][2] = { {R, 0}, {R/2, -H}, {-R/2, -H}, {-R, 0}, {-R/2, H}, {R/2, H}, {R, 0} }; polygon_2d BIGpoly; //A rectangle with a hexagonal hole in it assign(BIGpoly, outloop); //the rectangle BIGpoly.inners().resize(1); linear_ring<point_2d>& inner = BIGpoly.inners().back(); assign(inner, inloop); //the inner hexagon correct(BIGpoly); //correct the order iff not double a = 20.0; double h = a * sqrt(3.0) / 2; const double t1[][2] = { { 30+0, 10+0}, { 30+a/2, 10+h}, { 30+a, 10+0} }; const double t2[][2] = { { 0, 0}, { a/2, h}, { a, 0} }; const double t3[][2] = { {-10+0, -10+0}, {-10+a/2, -10+h}, {-10+a, -10+0} }; const double t4[][2] = { { 0, -15+0}, { a/2, -15+h}, { a, -15+0} }; const double t5[][2] = { {-50, -40}, {-110, 0}, {-100, 30}, {-50, -40} }; polygon_2d T1, T2, T3, T4, T5, T6; //the triangles assign(T1, t1); correct(T1); assign(T2, t2); correct(T2); assign(T3, t3); correct(T3); assign(T4, t4); correct(T4); assign(T5, t5); correct(T5); std::vector<polygon_2d > P_list, P_union, P_tmp; //the outer shape P_union.push_back(BIGpoly); DumbPPMPrint("c:\\BIGpoly.ppm", P_union.begin(), P_union.size()); //Case 1: floating triangle in hole P_union.clear(); ggl::union_inserter<ggl::polygon_2d >(BIGpoly, T1, std::back_inserter(P_union)); DumbPPMPrint("c:\\case1.ppm", P_union.begin(), P_union.size()); //Case 2: three solid triangle creating a small hole P_union.clear(); P_tmp.clear(); ggl::union_inserter<ggl::polygon_2d >(T2, T3, std::back_inserter(P_tmp)); DumbPPMPrint("c:\\case2_i.ppm", P_tmp.begin(), P_tmp.size()); ggl::union_inserter<ggl::polygon_2d >( (*(P_tmp.begin())), T4, std::back_inserter(P_union)); DumbPPMPrint("c:\\case2.ppm", P_union.begin(), P_union.size()); //Case 3: floating holed-polygon in hole //P_union.clear(); //contains result of case 2 P_tmp.clear(); ggl::union_inserter<ggl::polygon_2d >(BIGpoly, (*(P_union.begin())), std::back_inserter(P_tmp)); DumbPPMPrint("c:\\case3.ppm", P_tmp.begin(), P_tmp.size()); //Case 4: a triangle intersecting the hole from inside P_union.clear(); P_union.push_back(BIGpoly); P_union.push_back(T5); DumbPPMPrint("c:\\case4_pre.ppm", P_union.begin(), P_union.size()); P_union.clear(); ggl::union_inserter<ggl::polygon_2d >( BIGpoly, T5, std::back_inserter(P_union)); DumbPPMPrint("c:\\case4.ppm", P_union.begin(), P_union.size()); P_union.clear(); ggl::union_inserter<ggl::polygon_2d >( T5, BIGpoly, std::back_inserter(P_union)); DumbPPMPrint("c:\\case4_rev_order.ppm", P_union.begin(), P_union.size()); } void DumbPPMPrint(char *name, std::vector<polygon_2d >::iterator it, unsigned int n) { //WSQ Viewer can be of help //http://www.cognaxon.com/index.php?page=wsqview //the holes are black. //the more number of polygons are present at a pixel the brighter the pixel is. unsigned int imgwidth = 512; //pixel width of image unsigned int imgheight = 512; //pixel height of image float width = 400.0; //width of image: 10 units (e.g. meters) float height = 400.0; //height of image: 10 units (e.g. meters) //float width = 6000.0; //width of image: 10 units (e.g. meters) //float height = 6000.0; //height of image: 10 units (e.g. meters) //header FILE *signal = fopen(name, "wt"); fprintf(signal, "P3\n"); fprintf(signal, "# %s\n", name); fprintf(signal, "%d %d\n", imgwidth, imgheight); fprintf(signal, "255\n"); unsigned int x, y, i; float xpos, ypos; // PPM images carry red, green, blue color channels. int val0, val1, val2; std::vector<polygon_2d >::iterator poly; for (y = 0; y < imgheight; y++) { ypos = height/2 - height * y / imgheight; for (x = 0; x < imgwidth; x++) { xpos = width/2 - width * x / imgwidth; val0 = val1 = val2 = 0; //black ggl::point_xy<float> point(xpos, ypos); poly = it; for (i = 0; i < n; i++, poly++) { if( ggl::within( point, (*poly) ) ) { val0 += 255/n; val1 += 255/n; val2 += 255/n; } } //fi_poly // clamp to allowed range if (val0 < 0) val0 = 0; else if (val0 > 255) val0 = 255; if (val1 < 0) val1 = 0; else if (val1 > 255) val1 = 255; if (val2 < 0) val2 = 0; else if (val2 > 255) val2 = 255; fprintf(signal, "%3d %3d %3d ", val0, val1, val2); if (x%16 == 15) fprintf(signal, "\n"); } //fi_x } //fi_y fclose(signal); } //@End_of_Code

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C++ Networking Library Release 0.5
by Dean Michael Berris 09 Feb '10

09 Feb '10

Good day everyone, and I apologize in advance for the shameless plug. That said though, I'd like to announce the availability of version 0.5 of the C++ Network Library (cpp-netlib) on both Github and Sourceforge. For those interested in trying out a header-only being-developed-for-boost-inclusion networking library collection, you can download the latest release from: http://github.com/cpp-netlib/cpp-netlib/downloads or https://sourceforge.net/projects/cpp-netlib/ Active development happens on Github where the official repository is http://github.com/cpp-netlib/cpp-netlib (or via git) git://github.com/cpp-netlib/cpp-netlib.git While the cutting edge "clearing house" repository is the one I host also on Github http://github.com/mikhailberis/cpp-netlib (or via git) git://github.com/mikhailberis/cpp-netlib.git The latest release contains: * An HTTP 1.1 client * An embeddable HTTP 1.0 server template If you're interested in joining in on the development, please join the discussion at the cpp-netlib-devel mailing list at: https://lists.sourceforge.net/mailman/listinfo/cpp-netlib-devel or just fork my Github hosted repository -- then send pull requests when you feel like submitting your work "upstream" to me. We're currently in the process of moving on to implementing an HTTP 1.1 server template (looks like a Java Servlet Container), more efficient HTTP 1.1 client implementations, and other goodies. You can find documentation about cpp-netlib over at http://cpp-netlib.github.com/ Thanks in advance everyone and I hope this helps! -- Dean Michael Berris cplusplus-soup.com | twitter.com/deanberris linkedin.com/in/mikhailberis | facebook.com/dean.berris | deanberris.com

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