September 2010 - Boost-users - lists.preview.boost.org

Boost & Pthreads
by ef 13 Sep '10

13 Sep '10

Hello, I want to build a bunch of different graphs at once,and it looks like the best way to do this is with pthreads. I need to be able to communicate information between the graphs (sadly in real time). Is Boost pthread friendly? I am just thinking of calling read_graphviz per thread, and when a vertex is waiting for data from another graph it just sits and waits. Communication should be easy and done by shared memory. I dont see any problems with this. I am just curious before I take this path that Boost is pthread friendly, or atleast in the way that I described? Thanks, EF

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Re: [Boost-users] MSM & serialization
by Christophe Henry 13 Sep '10

13 Sep '10

>>> I'm planing to use the new MetaStateMachine library for a game. But i >>> want to create savegames with boost::serialization so i would need to >>> serialize the state machine. >>> There shouln't be too much to safe (the current state basically), but I >>> can't see how I can do this. >>> So, how can I do this? >> >> Hi, >> >> For the moment, unfortunately not at all, though it is something I >> want to do since a while and pretty high on my internal priority >> queue. >> How urgently do you need it? >> In the worst case, it would be easy to temporarily add a setter for >> the current state (we have a getter). >> >> Regards, >> Christophe > > Hi, > for the current project i just need 2 small state machines, so i can > hardcode them. But in the future it would really like to use MSM, at > thats impossible for me as long as i can't safe them. > So it's not very urgent, but if i could use it in 2 month, it would be > great. Hi, No, it won't be said so easily that MSM forces its users to hardcode state machines ;-) I just put something together and committed (without guarantee ;-) ) into the trunk. I also added into libs/msm/doc/HTML an example (Serialize.cpp) where you can serialize a state machine and even optionally states themselves (using a do_serialize typedef). It's not tested thoroughly in the little time I spent on it tonight and there are a few things I need to think about more but I hope it'll help you. Please keep me informed about your experience with this brand new feature ;-) Regards, Christophe

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MSM & serialization
by Christophe Henry 13 Sep '10

13 Sep '10

> I'm planing to use the new MetaStateMachine library for a game. But i > want to create savegames with boost::serialization so i would need to > serialize the state machine. > There shouln't be too much to safe (the current state basically), but I > can't see how I can do this. > So, how can I do this? Hi, For the moment, unfortunately not at all, though it is something I want to do since a while and pretty high on my internal priority queue. How urgently do you need it? In the worst case, it would be easy to temporarily add a setter for the current state (we have a getter). Regards, Christophe

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[Interprocess] Compile error when simply including managed_mapped_file.hpp in 1.44 using VC10
by Phil Ratzloff 13 Sep '10

13 Sep '10

Simply including managed_mapped_file.hpp in an empty project will generate an error in boost 1.44 using VC 2010. This doesn't occur in 1.43 and is a showstopper to me. Any ideas to work around this? I created a Console App using the New Project wizard. Here's the whole program: #include "stdafx.h" #include <boost/interprocess/managed_mapped_file.hpp> int _tmain(int argc, _TCHAR* argv[]) { return 0; } The following output log is generated: 1>------ Build started: Project: boost144Err, Configuration: Debug Win32 ------ 1> boost144Err.cpp 1>c:\lib\boost_1_44_0\boost\interprocess\detail\move.hpp(342): error C2440: 'return' : cannot convert from 'boost::interprocess::mapped_region' to 'boost::interprocess::mapped_region &&' 1> You cannot bind an lvalue to an rvalue reference 1> c:\lib\boost_1_44_0\boost\interprocess\mapped_region.hpp(159) : see reference to function template instantiation 'boost::interprocess::mapped_region &&boost::interprocess::move<boost::interprocess::mapped_region&>(T)' being compiled 1> with 1> [ 1> T=boost::interprocess::mapped_region & 1> ] 1>c:\lib\boost_1_44_0\boost\interprocess\detail\move.hpp(342): error C2440: 'return' : cannot convert from 'boost::interprocess::detail::file_wrapper' to 'boost::interprocess::detail::file_wrapper &&' 1> You cannot bind an lvalue to an rvalue reference 1> c:\lib\boost_1_44_0\boost\interprocess\detail\file_wrapper.hpp(63) : see reference to function template instantiation 'boost::interprocess::detail::file_wrapper &&boost::interprocess::move<boost::interprocess::detail::file_wrapper&>(T)' being compiled 1> with 1> [ 1> T=boost::interprocess::detail::file_wrapper & 1> ] 1>c:\lib\boost_1_44_0\boost\interprocess\detail\move.hpp(342): error C2440: 'return' : cannot convert from 'boost::interprocess::file_mapping' to 'boost::interprocess::file_mapping &&' 1> You cannot bind an lvalue to an rvalue reference 1> c:\lib\boost_1_44_0\boost\interprocess\file_mapping.hpp(62) : see reference to function template instantiation 'boost::interprocess::file_mapping &&boost::interprocess::move<boost::interprocess::file_mapping&>(T)' being compiled 1> with 1> [ 1> T=boost::interprocess::file_mapping & 1> ] ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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[fusion] Non-default initialisation of sequence components.
by Hugh Dickinson 13 Sep '10

13 Sep '10

Hi Everyone, I'm wondering if there is a (built-in) way in boost::fusion to instantiate a sequence of heterogeneous elements while passing an identical set of arguments to the constructor of each element? It seems like the only options are to default construct the elements or to supply references to previously constructed elements. As a semi-concrete example, is there a way to achieve the equivalent of the following? template <int Label> struct TestType { TestType(int i, double d, string s):I(i), D(d), S(s){} int I; double D; string S; }; int main(int argc, char* argv[]){ typedef vector<int, double, string> ArgVector; typedef vector<Type<1>, Type<2>, Type<3> > TypeVector; ArgVector args(1, 2.5, "hello"); // Want to pass the elements of Args as constructor arguments to each element of vec. TypeVector vec(args); } Any help much appreciated, Hugh

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[Unordered] No operator[] const?
by Hossein Haeri 13 Sep '10

13 Sep '10

Dear all, Is there any specific reason why there is no operator[] const for boost::unordered_map? Or, is that only an oversight? TIA, --Hossein

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MSM & serialization
by Jonathan 13 Sep '10

13 Sep '10

I'm planing to use the new MetaStateMachine library for a game. But i want to create savegames with boost::serialization so i would need to serialize the state machine. There shouln't be too much to safe (the current state basically), but I can't see how I can do this. So, how can I do this? Greetings Jona

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g++ compilation is slow with Boost's constructs
by Ilya Murav'jov 13 Sep '10

13 Sep '10

Hello, I've been using several Boost libraries since 1.33 and now I have a situation that it takes over 4 seconds to compile for some files <= 40Kb (not so big!), with gcc. I've upgraded my machine recently (AMD X3 425, 2700MHz, 2GB memory) and hoped that things would change but it is still somewhat a blocker to developing. So I began to investigate and found out each invocation of known Boost constructs has its non-zero cost. I chose a source file(*), commented out all and then incrementally uncommented functions from beginning, compiled and measured times. Here is my results (compile time, not run time!): - BOOST_FOREACH costs 0.1 sec - boost::function<> invocation costs 0.05 sec - boost::lambda::bind() with placeholders costs 0.1 sec - Boost.Range adaptor transformed() costs ~0.1 too As you can see, 10 boost::lambda::bind() slow down your compilation for whole 1 second! All that is measured against gcc 4.4, Ubuntu 9.10, with the most light options I picked up: "g++ -g -O0 -pipe" (I need -g for debugging anyway). Also I found out that gcc 4.2 is the quickest from 4.1, 4.2, 4.3, 4.4 version of gcc, and gcc 4.4 is the most slow one of them (~28% slower than gcc 4.2). :( Therefore, I have a few questions. 1) Are there more means/tricks for faster compilation with g++ I miss? (what a quickest gcc version?) 2) What compiler is known to be much more speedy for now, if any (icc, clang, msvc)? 3) Did someone try to investigate (and maybe fix) that gcc bottleneck(s)? Regards, Ilya Murav'jov (*) I did measures on a source file select.cpp from my project, Bombono DVD (http://gitorious.org/bombono-dvd/bombono-dvd/blobs/master/src/mgui/editor/s…)

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how could I output the data of matrix(ublas) to txt file faster?
by Samurai Deeper 13 Sep '10

13 Sep '10

Example /***********begin**************/ void testMatrixRow() { matrix<double> m(1920, 1080); clock_t begin,end; begin = clock(); for(unsigned int i = 0; i < m.size1(); ++i) for(unsigned int j = 0; j < m.size2(); j++) { m.insert_element(i, j, i*3 + j); } end = clock(); cout<<"time of inserting data : "<<(double)(end-begin)/CLOCKS_PER_SEC<<" "<<endl; ofstream ob1("testing.txt",ios::out,ios::binary); begin = clock(); for (unsigned i = 0; i < m.size1 (); ++ i) { for(unsigned int j = 0; j < m.size2(); j++) ob1<<m(i, j); } end = clock(); cout<<"time of regular output : "<<(double)(end-begin)/CLOCKS_PER_SEC<<" "<<endl; begin = clock(); for (unsigned i = 0; i < m.size1 (); ++ i) { matrix_row<matrix<double> > mr(m, i); ob1.write((const char*)&mr(0), mr.size()); ob1<<endl; } end = clock(); cout<<"time of nonregular output : "<<(double)(end-begin)/CLOCKS_PER_SEC<<" "<<endl; ob1.close(); } /***********end**************/ As expected,ob1.write is much more faster than ob1<< But the results are not I want(ob1<< is) Do I have any way to solve this problem? Thanks a lot -- View this message in context: http://old.nabble.com/how-could-I-output-the-data-of-matrix%28ublas%29-to-t… Sent from the Boost - Users mailing list archive at Nabble.com.

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follow to "[regex] Perl regex special characters"
by DBW 13 Sep '10

13 Sep '10

I found a thread from 2006-09-08 titled '[regex] Perl regex special characters' about whether ']' and '}' should be included in the documentation as characters that must be escaped. After spending quite some time today to discover that my '}' character did in fact need to be escaped, my opinion is that the documentation should be modified. Thanks, Brad

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Re: [Boost-users] [Polygon] Test among 3 libraries
by Angus Johnson 13 Sep '10

13 Sep '10

Simonson, Lucanus J <http://search.gmane.org/?author=Simonson%2C+Lucanus+J&sort=date> wrote: "I've never seen a comparison with clipper before, I've never heard of clipper and would like to learn more. Can you provide a link or reference? I found a sourceforge site with minimal description of clipper, but it left me with a lot of unanswered questions." Hi Luke. I'm the author of Clipper and am happy to answer your questions as best I can, but perhaps I can preempt some of them with a little background about Clipper and myself. Firstly, I've only recently created the Clipper library (ie within the last 3-4 months) and that may explain why you haven't heard of it. I originally wrote it in Delphi Pascal, but I've translated it into C++ too, and has been released with a Boost license. I wrote Clipper because I wanted a polygon clipping library (in Delphi) that wasn't encumbered with restrictive licensing. I'm still refining the library and have several updates in the pipeline (including polyline-polygon and polybezier-polygon clipping). Clipper is based on the Vatti clipping algorithm which places no restrictions on the types of input (subject and clipping) polygons. However, Vatti's original paper completely omits any discussion of 1. how to handle what I call 'complex' intersections - intersections involving more than 2 edges; and 2. how to handle overlapping horizontal edges. My Clipper library extends the Vatti algorithm by addressing both these issues. Clipper also extends the Vatti algorithm by implementing the NonZero polygon filling rule for input polygons (as well as Vatti's EvenOdd filling). I'm aware of one limitation of my Clipper library: because it uses floating point math it isn't 'robust' in the strict sense. However, errors (which are extremely rare) are properly trapped and reported as a failed clipping operation. In my testing ( see http://www.angusj.com/delphi/clipper.php#features ), Clipper has a number of advantages over GPC, a well known clipping library that's also based on Vatti's algorithm. Clipper - 1. is significantly faster; 2. properly handles complex intersections; 3. accepts both EvenOdd and NonZero filling input polygons; 4. doesn't require payment for commercial use. The SourceForge site for Clipper is: http://sourceforge.net/projects/polyclipping/ About myself: I've been writing computer code for 30yrs as a hobby. (I was a medical practitioner before I retired 15 yrs ago due to illness.) For the last 15 years I've been using Delphi (Object Pascal) and until now have never used C++. The C++ translation of my Delphi Clipper library is the first code I've written in C++ and should explain any unorthodoxy in my C++ coding style. (I'm aware that the C++ code is currently about 15% slower that the Delphi code so I suspect I'm not making the most of this language.) I'm very happy to receive constructive feedback and hope I can answer any questions too. Angus

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[Serialization] [Portable Binary]
by William Oquendo 12 Sep '10

12 Sep '10

Dear, In the documentation of boost::serialization, I read that there is still work needed to have a portable (32 and 64 bits) binary serialization implementation. The date of the TODO is 2008. Is still this a current TODO? is there a library implementing this? currently, It is not a matter of dead or live, but I would like to know. I have been trying to run a code in different (bits) systems, and I got the error "Incompatible native format - size of int" Best regards / Cordialmente, -- William Oquendo Phd Candidate Simulation Of Physical Systems Group Universidad Nacional de Colombia Linux User # 321481 ********************* Este correo puede carecer de tildes o eñes ya que el teclado no contiene estos caracteres. Presento excusas por eso. *********************

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[thread] boost::thread automatically detached when thread terminates?
by Boris Schaeling 12 Sep '10

12 Sep '10

Is a boost::thread object automatically detached when a thread terminates? I read in the Boost.Thread 1.44 documentation: "If the thread of execution represented by the boost::thread object has already completed, or the boost::thread object represents Not-a-Thread, then join() returns immediately." Is it really required to call join() or timed_join()? Or can I also call joinable() which would return false then? Boris

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[thread] basic question
by Sean Farrow 12 Sep '10

12 Sep '10

Hi: I am writing a cross platform application, I need to do the following: Firstly Launch a thread, which seems simple enough. Secondly, the thread function pols a port for input (midi, does assio support this?) Thirdly, I need someway of transferring data between the thread waiting for input and the main thread, what is the best way of doing this, in win32 I'd use Events. Finally, what is the best way of terminating the thread cleanly, in win32, I'd probably use a while loop of some sort.Any help appreciated! Regards Sean.

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fusion transform_view
by Hicham Mouline 12 Sep '10

12 Sep '10

Hello After I invoke the result_of::transform<Seq, UnaryFct> metafunction, the result type I get, printed out by typeid(...).name() gives transform_view< Seq, UnaryFct, void_ > is there a way to print out the actual resulting type, forcing the view to "evaluate" ? regards,

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[boost] [constrained_value] Constrained Value review results
by Gordon Woodhull 11 Sep '10

11 Sep '10

Greetings, Substituting for Jeff Garland, I am pleased to present the results from the constrained_value review. The library is available at http://rk.dl.pl/f/constrained_value.zip The documentation is at http://rk.dl.pl/r/constrained_value Enjoy! Gordon 1. History The idea for a constrained value library goes back to at least 2004; Christopher Diggins proposed a mini-library at that time. In 2007 Joe Gottman suggested that Jeff Garland's constrained_value.hpp in date_time could be a top-level library. Concurrently, Robert Kawulak (henceforth RK) was working on his own library for the purpose, which he also started in 2004, unaware of the others. RK announced his library on November 11, 2007. Discussion continued into 2008; on June 19, RK announced his library was ready for review and it was put in the queue. The review began on December 1 2008 and continued until around December 15 (with some trailing discussion of the definition of invariant and why exceptions should not be used to check invariants). Gordon Woodhull reviewed the thread's 260 messages in the summer of 2010 and produced this report, dividing the issues raised between those where there was consensus on a change, those where no resolution was found, and those where the author and requesters (mostly) agreed that no change was needed. 2. Votes Eight people voted for acceptance of the library; there were no "no" votes. However, many people stated conditions on acceptance. Thanks to Chris (indy271828(a)sympatico.ca) Vicente Botet, Zach Laine, John Maddock, Thorsten Ottosen, Stjepan Rajko, Daryle Walker, and Gordon Woodhull for providing reviews. (In addition, Paul Bristow provided a review which looks like a yes but does not explicitly say so.) Thanks also to David Abrahams, Kim Barrett, Neal Becker, Paul Bristow, Edward Diener, Jeff Flinn, Joe Gottman, Mathias Guanard, Mika Heiskanen, Giovanni Pierro Deretta, Thomas Klimpel, Michael Marcin, OvermindDL1, John Phillips, raindog, Ravi (lists_ravi(a)lavabit.com) Johan Råde, Sebastian Redl, Peter Simons, Steven Watanabe, Utku Yaman, and Deane Yang for participating in a very active discussion. 3. Issues to be Addressed Floating point By far the most contentious issue in the review was the statement in the library documentation that floating point is not supported, and a few reviewers made fixing this a condition on acceptance. The issue is that the x87 math instructions (which are the default for 32-bit Intel compiles) utilize 80-bit registers which are then rounded down to 64 bits when a double value is written to memory. This can cause two values which were not equal to become equal later, with fairly unpredictable behavior depending on optimization and what code intervenes between calculating a value and comparing it. One solution is simply not to use the x87 math instructions by enabling the SSE2 math instructions instead. However, users may want the extra precision, and there is no way for a library to control this option. A few reviewers confused this issue with the frequent need for fuzzy comparison with epsilon; it was shown that the bug can still appear with epsilon-based comparisons. Jeff Garland points out that the Boost Numeric Interval library, http://www.boost.org/doc/libs/1_42_0/libs/numeric/interval/doc/interval.htm has also dealt with the x87 and NaN problems. It uses the round-trip-to-memory approach for x87. There is potential to create constraints for constrained_value using numeric::interval, and perhaps any other fixes for floating point belong in that library. Many solutions were proposed; after debate there were four left standing: * Force the new value to be written to memory Kim Barrett suggested the following function, noting that it should not force a memory write unless the value is in a register. inline double exact(double const& x) { return *const_cast<double const volatile*>(&x); } Gordon Woodhull has tested this against example provided by Thomas Klimpel in a message titled "floating point FUD" of January 23, 2010 (http://article.gmane.org/gmane.comp.lib.boost.devel/198817) and it does work. However, many people objected to this solution because of efficiency concerns: it requires a round-trip to memory (or at least to cache) for every assignment. * Only allow >= or <= for floating point types, and make sure the bounds are truncated 80- to 64-bit truncation can cause two values to become equal, but if one of them is already truncated, it cannot cause them to swap order. Since it is likely that the value will be changed much more frequently than the bound, it would suffice to apply truncation just to the bounds when they are set, e.g. with the exact() function above. However it does not seem that this solution can work if the bounds are dynamically calculated; the library supports bounds being returned by an inlined function. Johan Råde also suggested that it might be possible to implement < and > in terms of <= and >= and the std::nextafter function. * Force the processor to use 64-bit precision Johan Råde mentions a floating point control register which could be used in http://article.gmane.org/gmane.comp.lib.boost.devel/183760 There were also mentions of possible assembly code solutions, but none were provided and this was generally unpopular because it requires someone very knowledgeable to maintain it. John Phillips argued that reducing the precision will "lose significance faster than expected". * Another interesting solution was suggested by Stjepan Rajko: that the test might not be the same as the invariant. This is what testing with epsilon would guarantee. If the value passes the test it is guaranteed to satisfy the invariant, but only the test and not the invariant is in code. So some values might be rejected which are okay, but no bad value is accepted. RK felt that any floating point solution should be implemented separately from constrained_value, because he does not have the expertise. But he should be willing to document the scope of the problem better, including the SSE2 compiler flags that avoid the problem altogether. The first solution (truncation of the value) does not seem to require any changes to the library. Truncating the bounds might require some extra customization points. NaN Another problem with floating point is NaN, which compares false with everything. It might be okay if the bounds inclusion test always returned false. But the closed range is implemented as !(x < lower) && !(upper < x). Stjepan Rajko suggested that it should always be compare(lower, x) && compare(x, upper) where compare is < for excluded bounds and <= for included. It seems like this solution would work well for floats but not necessarily for user-defined types, which might only define operator<(). Substitutability with the underlying type A few people requested the ability to set a compiler flag in order to substitute the constrained_value with the underlying type. This is not exactly possible, unless the user is willing to explicitly extract the value using static_cast<T>(cv). The library does provide unconstrained<> which in most cases optimizes away, but the interface is not perfectly compatible with the underlying type. Constraints not copied when operators used The use of operators invokes implicit conversion to the underlying type, which means that in a statement like constrained_value x(10, constraint(...)), y(-x); y ends up with uninitialized constraints. Steven Watanabe suggested that the operators could be overloaded, but RK argued that the behavior would be application-specific: "For some applications returning a constrained value would be OK (but again there is the problem that the constraint may reject the modified value) while for others it's better to return the underlying type." Constrained strings Jeff Garland offered that he has written constrained_string classes for allowing values from a set of strings, and for validation against a regex. RK said he might add a constraint type which validates against set<T>, and affirmed that a regex validator would be nice too. Bounding on only one side Utku Yaman and others requested a way to bound integers on only one side. RK noted that you could set one of the bounds to the maximum or minimum possible integer, but this is verbose. Default arguments would be confusing, and RK thought maybe he would supply lower_saturating_int and upper_saturating_int. Note that there is a more general problem, especially if floating point is allowed. (Also consider e.g. fixed point, rational.) Recoverable error policy - error policy changing the value There were some objections to the error policy taking three parameters - the new value, the member value, and the constraint. Does it really need to change the member value? Yes, RK explained, because this is a recoverable error policy. Vicente Botet asked that the concept be called RecoverableErrorPolicy. Serialization Neal Becker requested support for serialization. RK agreed this is worth looking into and pointed out a couple of difficulties. One, a way to not serialize empty (or static) policies is needed. Two, non-default constructible types such as odd_number might require use of load_construct_data() / save_construct_data() instead of serialize(). Rename bounded_int This class name does not convey the fact that the bounds are specified at compile time. Neal Becker suggested compile_time_bounded or static_bounded. RK says the first name is too long, and the second might imply that the bounds are static members (which is also a legitimate use case). sizeof static constrained types == sizeof underlying type Assuming that the empty base class optimization is being applied correctly, which seems to be the case, if the constraint and the error policy are empty, the size of the constrained value should be the same as the size of the underlying type. However, this was not the case on all platforms, at least at the time of the review. The library should include sizeof tests in its test suite so that potential users know if there is unexpected overhead on their platform. Specify static bounds as open<0>, closed<100> for bounded<> and bounded_int<> Requested by Vicente Botet. If possible, this would reduce the number of template arguments and would be more clear than the current bounds exclusion boolean parameters. Some default constructions may throw If zero does not satisfy the constraint, then a default-constructed constrained value may throw an exception. (There are other examples, like non-empty string.) Many reviewers requested a means to provide a default value, which can be done by wrapping the underlying type, but RK felt a default value class was out of scope. At the very least this should be documented and probably an example given. Examples Vicente Botet requested: * an example showing how to create a constrained class by derivation and/or containment which adds/removes methods from the constrained value interface * a date example where changing the month affects the bounds for the day. * example of static bounding on only one side * example of bounds calculated at runtime by a function ("runtime dynamic bounding") Others: * example of constraints with static members - allows shared mutable constraints with no overhead per instance. Tests! Many reviewers were offended that there were no tests in the review version. RK said he would write some. Documentation * document the concepts and provide tests with concept archetypes. It turns out that these are documented briefly in the doxygen documentation of constrained<> at http://tinyurl.com/39v8o6r, but many reviewers were expecting a section in the main document. * Stjepan Rajko pointed out that the constraint can't depend on mutable members of the underlying type, and wondered if there were other implicit requirements, such as the way copy construction or swapping works. He requested these be documented. * Gordon Woodhull suggests a section on space efficiency and which configurations should allow the size to be optimized to the same size as the underlying type, and spelling out in each example what the cost in space is. * Thorsten Ottosen requested benchmarks of non-checking unconstrained against just using the underlying type. RK offered that he had looked at the generated assembly on some platforms. 4. Unresolved debates Error policy is allowed to change constraint Vicente Botet objected to the "bounded object with memory" example, which tracks extremal values by setting the bounds to include any new values. And Thorsten Ottosen objected to the inefficiency of change_constraint using construct-and-swap: it's not necessary to swap the constraint unless it might be changed by the error policy. This seems to be an example of a monitored value, which RK does not want to write himself, so does it belong in this library? RK argued that it does no harm, so why not allow? Double-checking and disabling assertions A number of people were concerned with the inefficiency of first checking the constraint, and then also asserting that the constraint is satisfied after the assignment has happened or the error handler has been called. But RK argued that it was necessary to check the invariant to make sure that the assignment operator and the error handler are doing their job. Besides, it is possible to disable the asserts with either BOOST_DISABLE_ASSERTS or NDEBUG. There was some discussion of adding an assert policy or a specific macro (with no clear conclusion). Disabling checks There is unconstrained, which offers a way to replace one constrained type with an unconstrained type, but Chris (indy271828(a)sympatico.ca) requested a way to disable all checks with a single macro. It might not be good enough to use a single error policy and select between throwing version and an assign-anyway version, because the compiler won't always optimize this away. More members, less free functions Thorsten Ottosen thought that any functions which change the state of the object should be members, not free functions. In particular, change_constraint might be less efficient than possible because the construct-and-swap requires copying the constraint. This does seem to be partly an ideological debate. Specific classes instead of a general super-template Vicente Botet requested that the interface use specific classes instead of typedefs: currently many of the specializations, like bounded<>, are metafunctions that apply some parameters to the generic constrained_value and return a new type, and then the specific operations are free functions. Instead these could be full classes with member functions. RK argued that this would result in unnecessary duplication. Way to disable the arithmetic operators Vicente Botet requested a solution in code or in documentation for users who don't want the arithmetic operators defined. 5. Ideas not requiring any action Monitored Values Stjepan Rajko suggested (and Vicente Botet expanded on the idea) that constrained value is really a special case of a more general "monitored value" class, in which a monitor policy decides how to handle any assignment. So constrained value would be a monitored value where the monitor policy checks a constraint, possibly calls an error policy, and then asserts the constraint. RK did not want to implement this and resisted suggestions to allow the assertion to be disabled in order to allow this use case, because without an invariant, it's not really a constrained value. But he suggested that monitored value could be implemented by someone else and constrained value could be re-implemented in terms of it. "Monitored value" might not be the best name for the general class, because "monitor" suggests something passive, rather than something which controls the outcome of assignment. A way to run a function on a constrained value Stjepan Rajko requested a way to make a copy of the value, run a function on it, and then reassign back, preferring the syntax call_using_copy(f, x) to x = f(x). But he notes this could be written as a free function. Multiple ranges Edward Diener requested a way to supply multiple ranges, but agreed that the syntax would be unattractive. Assertions instead of exceptions Thorsten Ottosen requested a way to have only assertions and no exceptions, and RK pointed out that this can be done either by specifying an error policy which asserts, or even with an assign-anyway error policy, which leaves the invariant checking in place. Exclude bounds parameter Vicente Botet found it confusing that bounded_int takes false to mean include bounds and true to mean exclude the bounds. RK explained that this is an artifact of the way within_bounds is templated on a type which can be either a compile-time or a runtime value, e.g. mpl::true_ or bool; this technique means there can be no default argument to the constructor and thus the more common option must be false, the default constructed value of bool. Constraints between several variables. Vicente Botet suggested a sort of constrained_tuple where if you set one field it would affect the constraints for the other fields. E.g. a date object where the month and year would affect the valid range for the day. With the current interface you'd have to set the whole date at once. Constrained values as sets of instances Exploring the problem domain, Vicente Botet suggested another possible implementation of constrained value where the constrained value type keeps track of which instances satisfy the constraint. This class would offer a split operation which moves any instances which satisfy a more specific constraint into the new set. Changing the constraint would similarly return the set of instances which are now excluded. _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

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basic_file_source copy to filtering_streambuf
by Kraus Philipp 11 Sep '10

11 Sep '10

Hi, I have got a basic_file_source for reading a file. Can I copy the whole file into a filtering_streambuf, whithout closing the stream? I do this at this time with: std::ifstream l_file( "filename", std::ifstream::in | std::ifstream::binary ); std::copy( std::istream_iterator<char>(l_file), std::istream_iterator<char>(), std::ostreambuf_iterator<char>(&l_target) ) I would like to switch std::ifstream to basic_file_source. I can't use boost::copy because it close after writing my target stream. Do the basic_file_source hold a iterator, which I can use with std::copy? How can I do this? Thanks Phil

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Interaction between boost::timer and boost::thread
by Matthieu Brucher 11 Sep '10

11 Sep '10

Hi, I've decided to use boost::thread to run a background thread in my MPI application. Only one rank has a timer, and I only make some calls to elapsed(). Here is what I get if I print the values I retrieve from this single rank: 2.98 (...) 6.58 6.6 6.6 6.61 6.71 6.73 6.75 2.69 2.69 6.78 2.77 2.77 2.83 6.91 2.87 2.87 6.94 6.96 6.97 2.91 2.91 2.91 2.94 7.02 2.99 3.01 3.01 3.02 3.05 3.05 (...) You may notice that the values are not incresing, which leads to very bad total time in my case. Is there a known interaction between these two classes? I'm trying to create a simple example, but I can't get boost::timer to count sleep() time :| Matthieu Brucher -- Information System Engineer, Ph.D. Blog: http://matt.eifelle.com LinkedIn: http://www.linkedin.com/in/matthieubrucher

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[phoenix] function with reference implementation
by alfC 11 Sep '10

11 Sep '10

I noticed that in some contexts I have both the object class and the corresponding phoenix function class impl; ... impl f_impl; boost::phoenix::function<impl> f(f_impl); now to avoid the copying I could use: boost::phoenix::function<impl&> f(f_impl); which works. Although boost::phoenix::function<impl const&> f(f_impl); //doesn't work. (error below) Is there any problem with using references at all, in the first place? -- Thanks, Alfredo /home/correaa/usr/include/boost/spirit/home/phoenix/function/ function.hpp:31: error: conversion from ‘boost::phoenix::actor<boost::phoenix::composite<boost::phoenix::detail::function_eval<1>, boost::fusion::vector<boost::phoenix::value<gsl::interpolation::spline>, boost::phoenix::argument<0>, > > >’ to non-scalar type ‘boost::phoenix::actor<boost::phoenix::composite<boost::phoenix::detail::function_eval<1>, boost::fusion::vector<boost::phoenix::value<const gsl::interpolation::spline>, boost::phoenix::argument<0> > > >’ requested

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some problems about shared_ptr
by Samurai Deeper 11 Sep '10

11 Sep '10

I am a newbie of C++ and I have some question about the shared_ptr I think the best way to explain it is with an example: /*******beginning of CValue.h*************/ #ifndef TVALUE_H #define TVALUE_H template< typename tvalue > class CValue { public: CValue( tvalue value ) : value_(value) {}; private: tvalue value_; }; #endif /****end*************/ /*****Type.h***********/ #ifndef TYPE_H #define TYPE_H #include<boost/shared_ptr.hpp> /*template< typename tvalue > struct Type{ typedef boost::shared_ptr< CValue< tvalue > > pValue; };*/ template<typename T, template <typename> class Value> struct Type { typedef boost::shared_ptr< Value<T> > pValue; }; #endif /********end************/ what if I want to make it as a composition class? by example /***************example**********/ #include "Type.h" #include "CValue.h" template<typename T> class DIP //digital image processing { public: DIP(); virtual ~DIP(); shared_ptr < Type<T, filter> >createMediumFilter(); }; template<typename T> DIP<T>::DIP() {} template<typename T> DIP<T>::~DIP() {} template<typename T> shared_ptr< Type<T, filter> > DIP<T>::createMediumFilter() { typename Type<T, filter>::pValue c(new mediumFilter< T >); return c; } /*****************end**************/ I want to create the instance of mediumFilter like this in the main function int main() { Type<matrix<double>, Composition>::pValue C(new Composition<matrix<double> >); Type<matrix<double>, CValue>::pValue D; D = C->createCValue(); cout<<"system pause"<<endl; cin.get(); } how could I fix the problems? thanks -- View this message in context: http://old.nabble.com/some-problems-about-shared_ptr-tp29674340p29674340.ht… Sent from the Boost - Users mailing list archive at Nabble.com.

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How to manage the internal memory allocation in boost libraries?
by Tang Jiang Jun 11 Sep '10

11 Sep '10

Hello, I am seeking a way to manage the internal memory allocation in boost libraries, and it seems that most of boost libraries do not support allocator parameter, so they can not be handled like STL library. But for my project, our memory management need to control all the memory allocation even it happens in the third-party libraries. Could somebody give me some suggestions to accomplish that? Regards, Tang Jiang Jun

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[Unordered] Penultimate Iterator
by Hossein Haeri 11 Sep '10

11 Sep '10

Dear all, What is the quickest way to get hold of the penultimate iterator in an unordered_map? I'm aware of this one -- which is O(n), where n == container_.size(): container_type::const_iterator i = container_.begin(); advance(i, container_.size() - 1); Is there no O(1) solutions? TIA, --Hossein

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[Boost.Test] Understanding the correct use of BOOST_CHECK_CLOSE and BOOST_CHECK_CLOSE_FRACTION
by Torri, Stephen CIV NSWCDD, W15 10 Sep '10

10 Sep '10

I am trying to understand how to be use BOOST_CHECK_CLOSE and BOOST_CHECK_CLOSE_FRACTION for my problem. My problem is being able to check that two floating point values agree within 12 decimal digits. That is the difference between the two values is smaller than 1e-12. I see from the documentation that BOOST_CHECK_CLOSE requires a percent of agreement while BOOST_CHECK_CLOSE_FRACTION requires a fraction value. So when I used BOOST_CHECK_CLOSE_FRACTION to compare two value I got output that I didn't know how to read: /test_sgp4_orbit_data.cpp(52): error in "default_calculate_semi_major_test": difference{1e-12} between result{1.1219271770198256} and 1.1219271773271688{1.1219271773271688} exceeds 9.9999999999999998e-13 I used BOOST_CHECK_CLOSE_FRACTION as: BOOST_CHECK_CLOSE_FRACTION ( result, 1.1219271773271688, 1e-12 ); What I am intending is if 'result' and the value differ by more than 1e-12 then I have an error. If the difference is smaller than 1e-12 I wish to have the comparison succeed. From the output I don't know why the exceeds value is not written as '1e-12' since that is what I used. Where am I going wrong in my use of BOOST_CHECK_CLOSE_FRACTION? Stephen Stephen Torri, PhD NAVAL SURFACE WARFARE CENTER DAHLGREN 17214 Ave B Suite 121 Dahlgren, Va. 22448 540-653-1082 I am not a contracting officer. I cannot modify or initiate contracts, nor do I have the authority to financially commit the government in any way.

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[python] python 3 with boost 1.44, without using bjam
by Geoff Hilton 10 Sep '10

10 Sep '10

I'm working on a DLL that I would like to expose to Python as a module, but as I came into Python only when Python 3 was available, that's what I know and therefore would like to use. A while ago I took a stab at learning bjam, but for now I've reverted to regular msvc projects, I was able to compile boost.python initially with bjam when I updated to Boost 1.44, the result generated the following files of relevance: libboost_python3-vc90-mt-1_44.lib libboost_python3-vc90-mt.lib libboost_python3-vc90-mt-sgd-1_44.lib libboost_python3-vc90-mt-sgd.lib which is great.. but when I try to compile my project it looks for libboost_python-vc90-mt-1_44.lib or libboost_python-vc90-mt-gd-1_44.lib as appropriate. How can I make msvc compile it successfully? I know bjam is a compiler driver, so I imagine there's a way... (FYI, here are the compilation commands I use from a batch file when compiling a new boost release. I used to use the recommended commands but they stopped working when boost changed the naming conventions to use version-independent naming, probably because I hadn't modified project settings in some way, but a lot of projects would get effected, so after some fiddling this is what I came up with). start bjam --toolset=msvc variant=debug link=static threading=multi runtime-link=static stage start bjam --toolset=msvc variant=release link=static threading=multi runtime-link=shared stage Many thanks, Geoff Unrelatedly, a comment I think might be interesting (if only speculative): from what I recall, I think boost was partially influenced to switch to version-independent naming because (among other reasons) Microsoft was using the version-independence way of thinking via the .Net model with the GAC, but I found an article at one point (which I can no longer find) saying that they realized after much experience with .Net that it's actually still quite possible to get version/DLL conflicts as a result of the version-independence naming (I believe it had to do with GUID generation or some such thing, but don't quote me on that), and quite a lot harder to debug. As a result they would be rethinking .Net and/or changing to a model where version-dependence plays a more prominent role at some point in the future. I wish I could point out the article, but at any rate I know I remember thinking it was funny (if possibly unfortunate) that boost was switching to this new naming convention, a move partially influenced by Microsoft's current methodology in some capacity, after Microsoft had discovered this issue and would eventually be (as I understand it) reverting to what essentially equates to the traditional pre-.Net DLL where versioning can be a more important issue.

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Boost.accumulators : weighted_median
by Maximilian Matthe 10 Sep '10

10 Sep '10

Hi! I want to calculate the median color (along some other data) of the pixels of an image from its histogram: std::vector<int> m_Hist; // m_Hist[i] contains number of pixels with color i. using namespace boost::accumulators; accumulator_set<double, features<tag::weighted_mean, tag::weighted_median(with_p_square_quantile), tag::weighted_variance(lazy), tag::weighted_skewness >, double> acc; for(int i = 0; i < 256; i++) acc(i, weight = m_Hist[i]); float mm = weighted_mean(acc); float stdD = sqrtf(weighted_variance(acc)); float med = weighted_median(acc); float sk = weighted_skewness(acc); mean und stdD work correctly, but the median is too large. It gives me about 200, but the real value should be around 75 (I checked that manually). The skewness is around 11000 (which also seems quite large to me). So, what am I doing wrong with accumulators?

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