- Boost-users - lists.boost.org

RE: [Boost-users] Serialization problem loading a vector of items
by Foster, Gareth 25 Jan '05

25 Jan '05

I seem to remember being told that std::string was not meant to be inherited from, could it be the same in your case? -----Original Message----- From: boost-users-bounces(a)lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Bill Lear Sent: 24 January 2005 13:43 To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] Serialization problem loading a vector of items On Friday, January 21, 2005 at 12:29:37 (-0600) Bill Lear writes: >I am curious why loading a vector of items from an input stream fails >using one method but works using a slightly different method. >... I have not seen a response to this post. Along similar lines, I am having problems with sub-classing the std::vector class. I've tried multiple ways, but can't get it to load (de-serialize) properly. I've used private inheritance (my first choice), public inheritance. Neither work. Here is my attempt at public inheritance: template <class T> class RingBuffer: public std::vector<T> { public: RingBuffer() : _first_ind(0), _last_ind(0) { } double first() { return (*this)[_first_ind]; } double last() { return (*this)[_last_ind]; } void add(T v) { _last_ind = (_last_ind + 1) % size(); (*this)[_last_ind] = v; if (_last_ind == _first_ind) { _first_ind = (_first_ind + 1) % size(); } } private: int _first_ind; int _last_ind; friend class boost::serialization::access; template<class Archive> void serialize(Archive& ar, const unsigned int) { ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(std::vector<T>) & BOOST_SERIALIZATION_NVP(_first_ind) & BOOST_SERIALIZATION_NVP(_last_ind); } }; As before, I can save this to a stream, but cannot get it to load from a stream. I am using boost 1.32, with gcc 3.2. Bill _______________________________________________ Boost-users mailing list Boost-users(a)lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

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[string_algo] replace repeated char with single instance?
by Jeff Flinn 25 Jan '05

25 Jan '05

Am I required to use regex_finder to replace repeated chars with a single instance? I'm trying to cleanup a string for use with filesystem::path, for example: C:\\abc///def\\ghi => C:\abc\def\ghi There may be mixed forward and back-slashes. These are from environment variables that apparently are required by our use of NutCracker to support legacy apps under windows. If I need to use regex_finder what are the benefits of the string_algo versus just using the regex library? Thanks, Jeff

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C++ Template Metaprogramming - factorial example
by Brad Austin 25 Jan '05

25 Jan '05

Aleksey Gurtovoy wrote: > > Also, the first argument to eval_if is supposed to be an integral > > constant, and T4 is an expression of the form mpl::equal_to<T7,T8>, > > which again is just a nullary function, not an integral constant. > > Not if T7 and T8 are Integral Constants, see > http://www.boost.org/libs/mpl/doc/refmanual/equal-to.html. Okay, I see that now. Sorry, my mistake.

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Re: C++ Template Metaprogramming - factorial example
by Brad Austin 24 Jan '05

24 Jan '05

I wrote: > I recently purchased David Abrahams' and Aleksey Gurtovoy's new book > on the MPL, "C++ Template Metaprogramming" (obviously recently since > it's only been out a couple of weeks), and am working through some of > the examples. I'm having trouble with the factorial example in section > 8.3.1, page 160: > > #include <boost/mpl/int.hpp> > #include <boost/mpl/multiplies.hpp> > #include <boost/mpl/equal.hpp> > #include <boost/mpl/eval_if.hpp> > #include <boost/mpl/prior.hpp> > #include <boost/static_assert.hpp> > > namespace mpl = boost::mpl; > > template <class N> > struct factorial > : mpl::eval_if< > mpl::equal_to<N,mpl::int_<0> > // check N == 0 > , mpl::int_<1> // 0! == 1 > , mpl::multiplies< // N! == N * (N-1)! > N > , factorial<typename mpl::prior<N>::type> > > > > > { > BOOST_STATIC_ASSERT(N::value >= 0); // for nonnegative N > }; > > There's a minor issue in that equal.hpp is (apparently) mistakenly > included instead of equal_to.hpp, but even after fixing that, I can't > get this to compile in the form in which it's written. Should it, or > is it broken? After spending some more time on this I now believe the code is broken. There's some uncertainty because mpl::multiplies<> has apparently been either renamed or replaced with mpl::times<>, and only the latter is documented in the MPL Reference Manual, so I'm not certain whether or not the two behave identically. However changing "multiplies" to "times" didn't seem to make any difference in terms of the compilation errors, so in the analysis that follows I'm making the assumption that if there is any difference, it isn't doesn't change anything relevant to the problem at hand. According to the MPL Reference Manual, in an expression of the form mpl::times<T1,T2>, T1 and T2 must meet the requirements of an integral constant, not merely the weaker requirements of a nullary metafunction. In this case T2 is an expression of the form factorial<T3>, so for this to be vaild factorial<> must model an integral constant, not merely a metafunction *returning* an integral constant. However factorial<> derives from an expression of the form mpl::eval_if<T4,T5,T6>, and doesn't add any nested types or a value of its own. Therefore factorial<> only models an integral constant if mpl::eval_if<T4,T5,T6> does, which it doesn't. mpl::eval_if<T4,T5,T6>::type models an integral constant (provided T5:type and T6::type do), but mpl::eval_if<T4,T5,T6> is merely a metafunction returning that constant. Also, the first argument to eval_if is supposed to be an integral constant, and T4 is an expression of the form mpl::equal_to<T7,T8>, which again is just a nullary function, not an integral constant. So technically this would appear to be wrong, even though eval_if doesn't seem to mind in this case. FWIW, here's the final version of factorial<> I came up with. This version models an integral constant, and accepts for its argument either an integral constant or a nullary metafunction returning an integral constant: template <class N> struct factorial : mpl::if_< typename mpl::equal_to< typename N::type, mpl::int_<0> >::type, mpl::int_<1>, mpl::times< typename N::type , factorial< typename mpl::prior<typename N::type>::type > > >::type::type {}; Anyway, is this mailing list an appropriate place to bring up issues like this? I know David and Aleksey are members, but I'm not clear on whether their book qualifies as an official Boost product.

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Re: [Boost-users] boost::tuple problem
by Victor A. Wagner Jr. 24 Jan '05

24 Jan '05

At Saturday 2005-01-22 08:22, you wrote: > hello everyone, >     what's the difference between "tuple<int> t;"  > and  " tuple<int> t();" >why > tuple<int> t; > cout<<t; >is ok. >But > tuple<int> t(); this declares a function named t which takes no arguments and returns a tuple<int> it does NOT define a variable named t. > cout<<t; >make a link error. >I'm using >vs.net2003__________________________________________________________________»¶ÓÊ¹ÓÃACMAIL >ÓÊ¼þÏµÍ³ > > > >_______________________________________________ >Boost-users mailing list >Boost-users(a)lists.boost.org >http://lists.boost.org/mailman/listinfo.cgi/boost-users Victor A. Wagner Jr. http://rudbek.com The five most dangerous words in the English language: "There oughta be a law"

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Serialization problem loading a vector of items
by Bill Lear 24 Jan '05

24 Jan '05

I am curious why loading a vector of items from an input stream fails using one method but works using a slightly different method. Given a load method: template <class T> T* load(std::istream& in) { boost::archive::xml_iarchive ia(in); T* t; ia & BOOST_SERIALIZATION_NVP(t); return t; } and use of it: vector<item>* v = load<vector<item> >(std::cin); I get: uncaught exception: stream error But, when I use this load method: template<class T> void load(std::istream& in, std::vector<T*>& v) { boost::archive::xml_iarchive ia(in); ia >> BOOST_SERIALIZATION_NVP(v); } and use it so: vector<item> v; load(std::cin, v); it works perfectly. Is there some reason the first method should fail? Bill

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serialization library problems with MFC support for OLE Controls
by Muruganathan Annamalai 24 Jan '05

24 Jan '05

hi, Iam using VC6. I had problems using boost serialization library classes with MFC support for OLE controls. This is what I have, #include <afxctl.h> // MFC support for OLE Controls #include <boost/archive/text_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> ............. .............. When I compiled the code I got errors like, :\boost\boost-1_32\boost/archive/basic_text_iprimitive.hpp(72) : error C2039: 'char_type' : is not a member of 'IStream' D:\Devstudio_6.0\VC98\INCLUDE\objidl.h(4049) : see declaration of 'IStream' D:\boost\boost-1_32\boost/archive/basic_text_iprimitive.hpp(121) : see reference to class template instantiation 'boost::archive::basic_text_iprimitive<IStream>' being compiled D:\boost\boost-1_32\boost/archive/basic_text_iprimitive.hpp(72) : error C2065: 'char_type' : undeclared identifier D:\boost\boost-1_32\boost/archive/basic_text_iprimitive.hpp(121) : see reference to class template instantiation 'boost::archive::basic_text_iprimitive<IStream>' being compiled D:\boost\boost-1_32\boost/archive/basic_text_iprimitive.hpp(73) : error C2039: 'traits_type' : is not a member of 'IStream' D:\Devstudio_6.0\VC98\INCLUDE\objidl.h(4049) : see declaration of 'IStream' I think, error is because MFC has class called IStream. And the same name IStream is used as template parameter in the boost class. Is there anything I can do to overcome this problem. annamalai

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implicit conversion
by Benjamin Schmeling 24 Jan '05

24 Jan '05

Hi, I am working on exposing a bigint class to python. Now I've got the problem that methods which take an bigint as an parameter do not accept Python longs. For example: import _PythonLiDIA x=123L; c=_PythonLiDIA.bigint(); _PythonLiDIA.gcd(c,x); Traceback (most recent call last): File "test.py", line 132, in ? _PythonLiDIA.gcd(a,x); Boost.Python.ArgumentError: Python argument types in _PythonLiDIA.gcd(bigint, long) did not match C++ signature: gcd(LiDIA::bigint, LiDIA::bigint) I don't know how to achieve implicit conversion at this point, turning an long automatically into an bigint. The other way round, turning an bigint into long can be realized by defining __long__. Can someone help me please? Benjamin

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program_options usage question
by John Eddy 24 Jan '05

24 Jan '05

Hello, I was wondering if it is possible to have an option for which supplying an argument is optional. For example, suppose I have an executable called myprog and an option "o" that does something. Is it possible to allow both of the following command line syntaxes? myprog --o arg myprog --o Where in the second case I can programatically supply some default value? So the first would instruct the program to take the action associated with the "o" option using the supplied arg and the second would instruct it to take that action using the default argument value. I have been fooling with the default_value and implicit methods but neither seems to do what I want. Thanks, John Eddy johneddy(a)eng.buffalo.edu

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MPL vs BLL
by Roman 24 Jan '05

24 Jan '05

Hi. Any suggestion about mpl vs bll? Will they merge someday, or go concurrently? I haven't found anything on the net about it. I'm using bll currently. Thanks. Roman.

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