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uBLAS Matrix and Vector IO
by Pascal Bauer 24 Jan '05

24 Jan '05

Hi Boost-Users, Does Anybody know, whether there is a routine to save / read (double) Matrices in a BINARY format? Thanx in Advance. Pascal Bauer

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Tiny bug in boost::threads documentation (bibliographic reference)
by Andreas Wachowski 24 Jan '05

24 Jan '05

Hello, ok, this is, how shall I say it, more of a Knuthish bug, but a bug it is, so I might as well report it: In the bibliography of the boost:threads documentation, a reference is erroneous. It says [Hansen73] ACM Computing Surveys. Vol. 5. No. 4. December, 1983. Per Brinch. "Concurrent Programming Concepts" but instead it should be [Hansen73] ACM Computing Surveys. Vol. 5. No. 4. December, 1973. Per Brinch. "Concurrent Programming Concepts" (1973 instead of 1983) Best regards, Andreas

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passing shared_ptr<> by_value or by-reference?
by Kosta 23 Jan '05

23 Jan '05

Hi! Don't know, if this is a FAQ, but I couldn't find an answer to this question: Is there a common sense about how a shared_ptr<> should be passed to functions/methods: by-value or by-(const-)reference? 1) void test(boost::shared_ptr<A> a); 2) void test(boost::shared_ptr<A>& const a);

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Re: [Boost-users] boost::tuple problem
by Peter Dimov 23 Jan '05

23 Jan '05

heroboy 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(); > cout<<t; > make a link error. Because tuple<int> t(); is a function returning a tuple<int>.

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RE: [Boost-users] boost::tuple problem
by Shriram V 23 Jan '05

23 Jan '05

Hi, Your problem is a basic C++ problem, nothing to do with tuple<>s! Aren't you declaring a function with "tuple<int> t()" ? Thanks, -Shriram. | -----Original Message----- | From: boost-users-bounces(a)lists.boost.org [mailto:boost-users- | bounces(a)lists.boost.org] On Behalf Of heroboy | Sent: Saturday, January 22, 2005 8:53 PM | To: boost-users | Subject: [Boost-users] boost::tuple problem | | 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(); | cout<<t; | make a link error. | I'm using | vs.net2003________________________________________________________________ | __欢迎使用ACMAIL 邮件系统 | | | | _______________________________________________ | Boost-users mailing list | Boost-users(a)lists.boost.org | http://lists.boost.org/mailman/listinfo.cgi/boost-users

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Re: boost::tuple problem
by Franz Schnyder 23 Jan '05

23 Jan '05

heroboy schrieb: > hello everyone, >     what's the difference between "tuple<int> t;"  and  " tuple<int> t();" "tuple<int> t;" creates an instance of the type tuple<int>. "tuple<int> t();" declares a function t() with return type tuple<int>. If the constructor takes no argument you must create the instance without the brackets or the compiler takes it as a function declaration > why > tuple<int> t; > cout<<t; > is ok. > But > tuple<int> t(); > cout<<t; > make a link error. the linker can't find the definition of the function "tuple<int> t()" > I'm using vs.net2003__________________________________________________________________欢迎使用ACMAIL 邮件系统

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C++ Template Metaprogramming - factorial example
by Brad Austin 23 Jan '05

23 Jan '05

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? I'm using gcc 3.3-23 on Linux. The first meaningful line in the error novel I get is: error: no type named `tag' in `struct factorial<mpl_::int_<0> >' I was able to get a modified version to work, but only by explicitly invoking the eval_if metafunction and wrapping the result in a constant wrapper, like so: template <class N> struct factorial : mpl::int_< mpl::eval_if< mpl::equal_to<N,mpl::int_<0> > , mpl::int_<1> , mpl::multiplies< N , factorial<typename mpl::prior<N>::type> > >::type::value > { }; But as this is a less-than-trivial departure from the book version, I don't feel comfortable moving on without first gaining a better understanding of what's going wrong. Thanks in advance to anyone who can offer some insight.

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[program_options] How do I read a vector of strings?
by Matthew P. Cashdollar 22 Jan '05

22 Jan '05

Hello, I have been using program_options for a while and it works great. However, I don't know how to make a program which behaves like this: programname -blah abc -blah def -blah ghi In my code I would read the option blah as a vector of strings, like: po::options_description desc("Configuration"); desc.add_options() ("blah", po::value<vector<string>>(), "the location of the blah device") ; po::store(po::parse_config_file(config_file, desc), vm); po::notify(vm); etc. When I try to compile the code under MSVC++ 7.0 I get this error (among others): error C2947: expecting '>' to terminate template-argument-list, found '>>' Is it possible for me to do what I am trying to with the program_options library? Thanks, -Matt

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date_time::microsec_clock questions
by Donato Petrino 22 Jan '05

22 Jan '05

Hello, 2 questions regarding the microsec_clock: - Why it just have 'local_time()' but not 'universal_time()' member? (Analogous to the second_clock. I know that it can be converted to UTC, but its inefficient and I have to know in which time zone the program runs.) - For what reason "::std::time(&t)" in "microsec_time_clock.hpp:58" is called? gettimeofday()'s "tv->tv_sec" already has the sec's since 1.1.1970, so there is no need for this extra call. Is it a bug? Thank you in advance! -- Donato Petrino Petrino EDV-Beratung Darmstädter Str. 29 64331 Weiterstadt T +49 6150 5418-11 F +49 6150 5418-18 email: dpetrino(a)petrino-edv.de

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date_time and negative time_durations
by Erik Thiele 22 Jan '05

22 Jan '05

hi the docs of time_duration say that minutes() returns 0..59 and seconds() return 0..59. this is not true, the correct answer is, minutes() returns -59..+59 and seconds() also. the handling of negative durations is not fully documented. i.e. is it true that the sign of hours(),minutes() and seconds() is always equal to each others sign? x=time_duration(anything...); y=x.invert_sign(); is the following true for all values of x: abs(x.hours()) == abs(y.hours()) abs(x.minutes()) == abs(y.minutes()) abs(x.seconds()) == abs(y.seconde()) but whatever way you document it, it should somehow be documented. to continue on my work i now make the assumption that in the following assertions are true for all values of x: if (x.is_negative()) x = x.invert_sign(); assert(x.hours()>=0); assert(0<=x.minutes()<=59); assert(0<=x.seconds()<=59); i hope this assertions are correct for all values of x !!!!! :) cya! erik

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