September 2004 - Boost - lists.boost.org

lambda: missing result deduction
by David Abrahams 02 Sep '04

02 Sep '04

I had to add this to get some tests for the TMP book to pass: namespace boost { namespace lambda { template<int N> struct plain_return_type_2<arithmetic_action<plus_action>, char[N], std::string> { typedef std::string type; }; }} // namespace boost::lambda Obviously this could be generalized for basic_string and for the reversed arguments. I assume it's not in the library because it forces you to #include <string>? Maybe there should be a special lambda header for each std:: type that needs deduction help? -- Dave Abrahams Boost Consulting http://www.boost-consulting.com

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Get/set state in Mersenne Twister
by Neal D. Becker 02 Sep '04

02 Sep '04

In order to serialize, it would be helpful to add an interface to mersenne_twister to get/set the state. I don't think there is any I/F to get the state.

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Fw: Boost in Software 2.0 Extra! magazine
by John Maddock 02 Sep '04

02 Sep '04

This one may be of interest to a some our continental developers: > Hello, > > We are currently working on an issue of our Software 2.0 Extra! magazine > devoted exclusively to C/C++ programming using crossplatform libraries. > The Boost project is widely known and its constituent libraries are used > by many programmers all over the world, so it would be great if we had > something about it in our magazine. > > Would you or anyone else from the Boost development team be interested > in writing an article on C/C++ programming with Boost for our magazine? > We can agree on a specific subject later on. > > Our magazine appears in four language versions: Polish (Poland), French > (France, Belgium, Canada), German (Germany, Austria, Switzerland) and > Spanish (Spain, Portugal) with a total circulation of about 30000. Each > issue is devoted to a different area of IT. > > Please let me know if you are interested in cooperating with us on this > issue. > > Best regards, > > Zbigniew Banach > > -- > Software-Wydawnictwo Sp. z o.o. > ul. Lewartowskiego 6, 00-190 Warszawa > tel.: +48 22 860-17-60 > fax.: +48 22 860-17-71 > www: http://www.software20.org > e-mail: zbyszek(a)software.com.pl > >

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another bjam question
by Robert Ramey 02 Sep '04

02 Sep '04

When I build and run config_info using msvc-stlport I get the output below which doesn't seem correct. I get no reference to stlport. When I investigate the bjam output I find (for another test) I find that the following is being used for the command line: "cl" /Zm800 -nologo /EHsc -c -D_STLP_DEBUG=1 -D_STLP_DEBUG_UNINITIALIZED=1 -D_STLP_USE_DYNAMIC_LIB=1 /Z7 /Od /Ob0 /EHsc /GR /MDd -I"C:\BoostMainCVS" -I"c:/Program Files/microsoft visual studio\vc98\include" -I"c:\STLport-4.5.3\stlport" -Fo"..\..\..\bin\boost\libs\config\test\no_ded_typename_fail.test\msvc-stlpo rt\debug\threading-multi\no_ded_typename_fail.obj" -Tp"..\..\..\libs\config\test\no_ded_typename_fail.cpp" This indicates that the Microsoft native include is specified BEFORE the STLPort one. This would explain why the config_info doesn't reflect the STLPort usage. Can someone tell me what I should be doing differently? Robert Ramey Microsoft Visual C++ version 6.0 _CPPUNWIND =1 __cplusplus =1 _M_IX86 =500 _WIN32 =1 _WCHAR_T_DEFINED [no value] _CPPRTTI =1 _DLL =1 _MSC_EXTENSIONS =1 _MSC_VER =1200 _MT =1 __BOOL_DEFINED =1 ********************************************************************* Dinkumware standard library version 1.x ********************************************************************* Detected Platform: Win32 Type char is signed Type wchar_t is unsigned byte order for type short =0 8 byte order for type int =0 8 16 24 byte order for type long =0 8 16 24 sizeof(wchar_t) =2 sizeof(short) =2 sizeof(int) =4 sizeof(long) =4 sizeof(size_t) =4 sizeof(ptrdiff_t) =4 sizeof(void*) =4 sizeof(void(*)(void)) =4 sizeof(float) =4 sizeof(double) =8 sizeof(long double) =8 CHAR_BIT =8 CHAR_MAX =127 WCHAR_MAX =((wchar_t)-1) SHRT_MAX =32767 INT_MAX =2147483647 LONG_MAX =2147483647L ********************************************************************* Boost version 103100 BOOST_USER_CONFIG =<boost/config/user.hpp> BOOST_COMPILER_CONFIG ="boost/config/compiler/visualc.hpp" BOOST_STDLIB_CONFIG ="boost/config/stdlib/dinkumware.hpp" BOOST_PLATFORM_CONFIG ="boost/config/platform/win32.hpp" BOOST_BCB_PARTIAL_SPECIALIZATION_BUG [no value] BOOST_DEDUCED_TYPENAME [no value] BOOST_FUNCTION_SCOPE_USING_DECLARATION_BREAKS_ADL [no value] BOOST_HAS_DECLSPEC [no value] BOOST_HAS_FTIME [no value] BOOST_HAS_MACRO_USE_FACET [no value] BOOST_HAS_MS_INT64 [no value] BOOST_HAS_THREADS [no value] BOOST_HAS_WINTHREADS [no value] BOOST_MSVC =1200 BOOST_MSVC_STD_ITERATOR =1 BOOST_MSVC6_MEMBER_TEMPLATES [no value] BOOST_NESTED_TEMPLATE =template BOOST_NO_ARGUMENT_DEPENDENT_LOOKUP [no value] BOOST_NO_ARRAY_TYPE_SPECIALIZATIONS [no value] BOOST_NO_CV_VOID_SPECIALIZATIONS [no value] BOOST_NO_DEDUCED_TYPENAME [no value] BOOST_NO_DEPENDENT_TYPES_IN_TEMPLATE_VALUE_PARAMETERS [no value] BOOST_NO_EXPLICIT_FUNCTION_TEMPLATE_ARGUMENTS [no value] BOOST_NO_FUNCTION_TEMPLATE_ORDERING [no value] BOOST_NO_HASH [no value] BOOST_NO_INCLASS_MEMBER_INITIALIZATION [no value] BOOST_NO_INTEGRAL_INT64_T [no value] BOOST_NO_INTRINSIC_WCHAR_T [no value] BOOST_NO_LONG_LONG_NUMERIC_LIMITS [no value] BOOST_NO_MEMBER_TEMPLATE_FRIENDS [no value] BOOST_NO_MEMBER_TEMPLATES [no value] BOOST_NO_MS_INT64_NUMERIC_LIMITS [no value] BOOST_NO_PRIVATE_IN_AGGREGATE [no value] BOOST_NO_SFINAE [no value] BOOST_NO_SLIST [no value] BOOST_NO_STD_ALLOCATOR [no value] BOOST_NO_STD_ITERATOR [no value] BOOST_NO_STD_ITERATOR_TRAITS [no value] BOOST_NO_STD_MIN_MAX [no value] BOOST_NO_STD_OUTPUT_ITERATOR_ASSIGN [no value] BOOST_NO_STD_USE_FACET [no value] BOOST_NO_STDC_NAMESPACE [no value] BOOST_NO_SWPRINTF [no value] BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION [no value] BOOST_NO_TEMPLATE_TEMPLATES [no value] BOOST_NO_TEMPLATED_ITERATOR_CONSTRUCTORS [no value] BOOST_NO_USING_TEMPLATE [no value] BOOST_NO_VOID_RETURNS [no value] BOOST_STD_EXTENSION_NAMESPACE =std BOOST_UNREACHABLE_RETURN(0) [no value] EXIT STATUS: 0

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Compilation problem of ublas
by Matthias Troyer 02 Sep '04

02 Sep '04

Hi, Doing a cvs update of the Boost CVS I encountered a compiler bug in ublas: ...boost/boost/numeric/ublas/matrix_sparse.hpp:2556: error: no matching function for call to `boost::numeric::ublas::unbounded_array<size_t, std::allocator<size_t> >::unbounded_array() Is there a problem in the constructor of matrix_sparse, or is the missing default constructor of unbounded_array the problem? Could one of the ublas developers look into this problem? Matthias

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name mangling scheme for tru64cxx65
by Markus Schöpflin 02 Sep '04

02 Sep '04

Hello! Currently, the name mangling scheme used on this platform is the default one selected by the compiler. It turns out that this is a bad choice when compiling boost. The problem is illustrated by the following example: ---%<--- #include <iostream> using namespace std; template <typename T> void foo(T const &x) { cout << "1" << endl; } template <typename T> void foo(T * const &x) { cout << "2" << endl; } int main() { foo("abc"); return 0; } --->%--- This prints out "2" with the default name mangling scheme. When manually selecting "ansi" as the name mangling scheme, the correct result "1" is printed. Therefore I propose to explicitely set the name mangling to ansi in the tools file for this compiler. Does anyone have any strong feelings or arguments against such a change? Markus

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C++ random container
by AngleWyrm 02 Sep '04

02 Sep '04

A proposal for inclusion into the boost libraries: ----------------------------------------------- The hat container derives it's name from the act of pulling names from a hat. It is a container which provides random selection of it's contents, where the items can have differing probabilities, and can either be removed like cards from a deck, or come up again like rolling dice. Rationale ======= There are easy ways to generate uniform chance containers. If one wishes to roll a die, it's a simple matter of scaling a random number to the appropriate range, and then picking from an ordered set. If one wishes to draw cards from a deck, then it is also easy to place all the cards in a container and perform a random_shuffle, then take as many as desired from one end. In 1977, A.J. Walker published a method for the non-uniform first case, in "An Efficient Method for Generating Discrete Random Variables with General Distributions" to the ACM, and Donald Knuth, in his second volume of The Art Of Computer Programming, "Seminumerical Algorithms" presents an implementation of Walker's alias algorithm. This alias technique is very efficient when the probability distribution is fixed before selection, and answers a large subset of uses. It performs in constant time, once a table has been set up, which requires linear time. But there is still one class of problem left out. In the case where the distribution changes dynamically as choices are added to or removed from the set, the above technique must recalculate a lookup table for each insert/delete operation, a linear-time operation. Examples of this problem space are: Drawing lottery balls, random selection from a changing client list, or situations where a random sample is taken before all data is gathered. The hat container provides a solution for all four of the above scenarios: uniform and non-uniform distributions, both with and without replacement. Furthermore, it performs these functions with a time complexity of O( log n ). -:|:- AngleWyrm hat container and documentation at http://home.comcast.net/~anglewyrm/hat.html

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RE: Serialization questions
by Robert Ramey 02 Sep '04

02 Sep '04

> Hello again, > > I have started using your serialization library. It is working pretty > well, but I have run into a few small problems: > > 1) No serialization for bitset: No big deal, because I can just > convert to ulong, but I was surprised it wasn't there. Feel free to add it in along with a test. I would like to see people adding serialization bit by bit to the existing data structures as the need becomes apparent. We're coming to the view that these things should be added to the data structures themselves rather than the serialization library. I'm trying to get myself out of the business of serializing things. > > 2) I have a text archive with a bunch of pairs of strings. I want to > append another pair. There doesn't seem to a way to append items > to an archive. LOL - an interesting question that only recently - (in the last couple of months) occurred to me. There is no reason that you can't create an archive and just append to it as many times as you see fit. Oa << t; ... Oa << t; EXCEPT that the t (and its constituents) should have its serialization trait set so that memory tracking is turned off. Otherwise, copies subsequent to the first one won't copy any data - just a pointer to the original. I have considered making and testing an example of such a thing, but I've been busy. To support this and make a good example what is really needed is: a) another archve construction flag - "no_tracking" to suppress memory tracking for the archive regardless of the setting for each individual type. b) serialization added to boost::any and/or boost::variant. Probably doable but maybe a little tricky. In this way one could just save willy-nilly anything to the archive and load later. This would be very interesting for things like database transaction logs which want to implement rollback/rollforward and things like that. It would also make a dynamite log for debugging. Again, feel free to explore this at your leisure. > 3) similarly, if I'm reading items from an archive, there is no simple > way to keep reading until the end of the file. I have to catch the > exception, which seems wrong for such an unexceptional > circumstance. Setting a fail bit as with streams would be nicer. Checking the fail bit on the stream before reading the next archived item should work. It's intended to anyway. If it doesn't work it's a bug. There might be a little tweaking required as I didn't test for this specifically. If you try this and it doesn't work and you find the oversight let me know and I'll add the fix. Better yet, make and test a small test and submit it to me and I'll add it into the test suite. > However, you could take the view that you should always know what > is in the archive, and to have a method of failure that does not > throw an exception would invite errors. That suggests that a > constructor flag might work (e.g. throw_on_eof default to true). I recently discovered that one can set a flag on an input stream so that an attempt to read past eof will throw an exception. This would leave all options open. After learning ths I'm considering removing the code that checks the fail bit as I would like to leave the flexibility for the user and make the serialization library smaller. BTW the fail bit means - "the next operation is expected to fail", NOT "the last operation failed". This confused me for quite a while until I actually carefully read the documentation for stream rather than presuming what I thought was obvious. > 4) A minor point: It would be nice to be able to construct an archive > with a boost::filesystem::path, instead of creating an fstream and > then using that to create the archive. It is certainly nice that I > can attach an existing stream to an archive, but directly using a > path would reduce some clutter. It would also make it a little > safer, because I couldn't accidently insert something into the > stream that was not serialized. Feel free to make your own - it should be trivial exercise. It should be easy to do deriving from any of the current archives. Polymorhphic archive works this way. Its one template that "adapts" any archive it's applied to. Also the current setup is specifically designed to permit serialized data to be embedded within some other data stream if the user requires it. I haven't specifically tested this either. > I have read large parts of the discussions when you were submitting > your library, but not all. If I have missed something, you can just > point me to it. Seems like you've pretty much got it. The thing that takes special care is the serialization of pointers through abstract base pointers. This works fine but there are a couple of non-intuitive aspects that can trip you up. The manual is pretty complete. This is mostly because I kept adding to it as questions kept coming up on the list. So I would hope that one can understand and use the package without going back and trolling through the list. If you don't mind, I'm posting this to the list. Your questions are interesting, good grist for the list, and help diminish the frequency of the same questions getting asked multiple times. Robert Ramey

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IOStream mmap too restrictive?
by Neal D. Becker 01 Sep '04

01 Sep '04

"Files must exist before being opened, and are never truncated; attempting to write past the end of a file results in an error. " This is quite restrictive, compared to the capabilities of posix mmap. Are these restrictions really necessary?

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lambda; ->*
by Goran Mitrovic 01 Sep '04

01 Sep '04

Is it normal that boost lambda's member pointer operator fails on member functions that have throw() modifier? Compiler is VC7.1. Is there a solution?

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