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[C++ Template Metaprogramming] Selected Answers Posted
by David Abrahams 28 Mar '05

28 Mar '05

Ariel Badichi has generously established a wiki page containing his answers to many of the exercises in the book "C++ Template Metaprogramming: Concepts, Tools, and Techniques from Boost and Beyond" by me and Aleksey Gurtovoy. Please see the book's home page at http://www.boost-consulting.com/metaprogramming-book.html for details. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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[comp.lang.c++.moderated] question about dynamic_any
by David Abrahams 28 Mar '05

28 Mar '05

FYI. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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Cleaning delete
by Igor Smirnov 28 Mar '05

28 Mar '05

Hi All, What do you think about optional set of new/delete operators which clean memory in delete() by filling it with zeros. I mean an implementation with the standard syntax, so that any old program using the standard new/delete can be linked with the modified version of new/delete without any change in the program text and even without its recompilation. I have never heard whether this simple idea was implemented anywhere. In fact, these operators are useful for sequre aplications, which are not expected to leave significant information in the dynamic memory. This is also useful for debug of any program that uses direct allocations with raw pointers, the style which it known to be prone to errors. The use of already deleted information is more likely to be detected, if this information is physically deleted. The cleaning new/delete operators might be made very simple (almost trivial, except exception safety) and perhaps completely portable. Does this idea look useful? Regards Igor Smirnov

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size limit on files in Sandbox File Vault
by Eric Niebler 28 Mar '05

28 Mar '05

I just tried to upload a new version of xpressive to the Boost Sandbox File Vault, and I received this error: "A file with the name xpressive.zip exceeds maximum allowed size (256 Kb)!" This seems pretty restrictive. The PDF version of xpressive's docs by itself exceeds this limit! I want to include the source code, the regression and perf tests, PDF and HTML documentation, and samples in a single download, but my .zip weighs in at 444 Kb. Can the limit be increased? -- Eric Niebler Boost Consulting www.boost-consulting.com

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Re: [boost] [mpl] float representation
by Cromwell Enage 28 Mar '05

28 Mar '05

--- Andy Little wrote: --- > What is the rationale for the 4 different types > representing rational fractions? Presumably you mean fraction, fraction_c, rational, and rational_c? The fraction_c struct template is simply a metafunction that returns a fraction type, and the rational_c struct template returns a rational type. (Or was it the other way around?) The fraction struct template covers a smaller range of numbers than the rational struct template, but the rational struct template models the concept of a mixed number, which consists of a whole number part and a fraction part, so I figured both the fraction and rational representations were essential. It certainly made implementation simpler. > What is the rationale for making the numerator and > denominator types in fraction_c? In an earlier version, the numerator and denominator were defined by BOOST_STATIC_CONSTANT. Looking through the Integral Constant Guidelines and the MPL source code, I read that certain compilers were likely to complain about the very code I used to have: BOOST_STATIC_CONSTANT before typedef statements, fraction_c<long,7,8>::value inside macros, etc. Not that I have these compilers on hand, but I figured I wasn't making this sub-library just for myself, either, so I searched for a better representation. Lo and behold, Aleksey Gurtovoy created a set of arithmetic metafunction classes that do the dirty work for me. I simply built on top of his work. Thanks for your interest! Cromwell D. Enage __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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Binary files in CVS
by Peter Dimov 27 Mar '05

27 Mar '05

The following files in the main CVS are binary but do not appear to be marked as such: M libs/program_options/test/ucs2.txt M libs/program_options/test/utf8.txt M libs/ptr_container/doc/cboost.gif The sandbox CVS also contains such files: M boost/ptr_container/ptr_container.tgz M libs/numeric/bindings/doc/c++boost.gif M libs/ptr_container/doc/cboost.gif M libs/sequence_algo/doc/cboost.gif These are corrupted by the Windows CVS clients on every checkout via CR insertion. The easiest way to avoid this is to just not check in binary files in the CVS. -- Peter Dimov http://www.pdimov.com

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Serialization issuses under MS VC++ 7.1 ....
by jason 27 Mar '05

27 Mar '05

I'm all new to C++, let alone Boost, so do excuse me if this is a dumb post, I've only been using C++ for a few weeks now, and come froma web design background. Anyway, I am getting a Error C2780 .\boost_1_32_0\boost\serialization\split_free.hpp(45): error C2780: 'void boost::archive::save(Archive &,const T &)' : expects 2 arguments - 3 provided message when I use STL containers in Boost and the BOOST_SERIALIZATION_SPLIT_MEMBER() macro in my class. I have found when I don't split the serialize method into load / save methods it works fine. However, I need separate load / save methods as some of the members in my class are not serializable (they are SDL resources, and therefore uploading I need to do some other work to restore these members). Here is a chunk of example code that fails... class P { private: int qw; friend class boost::serialization::access; template<class Archive> void serialize(Archive& ar, const unsigned int version) { ar & qw; } public: P() : qw(0) {} P(int Qw) : qw(Qw) {} }; typedef std::list<P*> pList; class Test { pList p; friend class boost::serialization::access; BOOST_SERIALIZATION_SPLIT_MEMBER() template<class Archive> void load(Archive& ar, const unsigned int version) { ar & p; } template<class Archive> void save(Archive& ar, const unsigned int version) const { ar & p; } public: Test() {} }; Using Test t; std::ofstream ofs("frameTest"); boost::archive::text_oarchive oa(ofs); oa << t; ofs.close(); creates this error. To me it seems like this might be a library issue. However could someone point out what I am doing wrong if it is me, and if it is a lib issue, could they hint /suggest some sort of cleanish workaround. I am going to mess about and hack together a workaround by not splitting the serialize method into load/save methods in the class affected for now, however I'm sure other people on this list will be able to suggest better solutions than mine. And yes, I am including the list.hpp file incase anyone thinks I'm not including it. Jason.

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[date_time] missing includes?
by Russell Hind 27 Mar '05

27 Mar '05

I'm just trying date_time on OS X. I've included #include <boost/date_time/posix_time/ptime.hpp> #include <boost/date_time/posix_time/conversion.hpp> This fails to compile with the following error. Including posix_time.hpp rather than ptime.hpp or a gregorian header solves the problem. posix_time/conversion.hpp:33: error: 'to_tm' undeclared in namespace 'boost::gergorian' posix_time/conversion.hpp:45: error: 'date_from_tm' undeclared in namespace 'boost::gregorian' Should the appropriate header be included by posix_time/conversion.hpp? Cheers Russell

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rational variants/alternatives
by Andras Erdei 26 Mar '05

26 Mar '05

i've started to work on the variants that were brought up in a previous discussion about boost::rational<> the current code can be found at www.ccg.hu/pub/src/rat atm it is only for getting the calculations right, so no templates, optimizations, boostification, nice interface etc, and i only tested it with MSVC 7.1 there is also no implementation yet geared towards an unlimited precision representation the variants are: - legacy boost (no rounding, silently gives wrong results) - exceptions are thrown if the result overflows or cannot be represented - rounding - rounding & maintaining an exactness indicator is there anything missing from the list? there is also a simple test-bed, it runs the four basic operations 10000 times on random inputs, and collects some statistics: addition and substraction overflowed 0 times, and the result was exactly representable 44 times; the average error of the legacy code is 475%, and of the rounding code is 0.005% (the exception-throwing variant throws, so there is no error figure for that) multiplication and division overflowed once, and the result was exactly representable 79 times; the average error of the legacy code is 2025%, and of the rounding code is 0.01% it would be nice to get some advice on how the final interface should look like (and of course regarding everything else, including whether there is a point to continue the work): - any ideas for naming the variants? - how should the parameters of rational<> look like? my favourite would be rational<prec,method> where prec is the maximum absolute value allowed for numerators and denominators, and method is one of the variants from above, e.g. rational<10000,round> would be a rounding rational with four decimal digits for the numerator and denominator. of course this would cripple rational<> to be int-based, so maybe specifying the number of bits to be used instead of the maximum value is a sensible approach. (still don't know though how would user-defined types be selected based on this, so maybe the original boost approach is the only workable one.) br, andras ps: i have tried to search the archive for past discussions about rational<> to avoid repeating old stuff, but with very limited success (only the latest posts seem to be accessible) -- any hints?

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boost::is_convertible failure on abstract classes
by Me here 26 Mar '05

26 Mar '05

Hello, The code below does not compile, when, I believe, it should. Compiler says that you can't instantiate abstact class. I'm really surprised - it is trivial use case, but I did not find a problem report. Do I miss something? Regards, Alexander --------------- sample code ------------ #include <boost/static_assert.hpp> #include <boost/utility/enable_if.hpp> #include <boost/type_traits.hpp> struct Data { virtual foo() =0; }; int main(int argc, char* argv[]) { BOOST_STATIC_ASSERT((boost::is_convertible<Data,Data>::value)); return 0; } --------------- sample code ------------ __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new resources site! http://smallbusiness.yahoo.com/resources/

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