- Boost - lists.boost.org

Using Bind & Lambda
by Robert Jones 11 Jun '08

11 Jun '08

This is my first time posting to this list, so I hope you'll forgive me it my etiquette is awry. I'm new to the Boost libraries, and just learning my way around, guided mainly by Bjorn Karlson's book - any other book recommendations would be most welcome btw, and there a few things I just don't quite get! First - is "boost/lambda/bind.hpp" equivalent to "boost/bind.hpp"? Should it ever be necessary to include both? Second - Is it true that a lambda function is syntactically and semantically the same as a bind finction, eg Given:- int foo( int i ) { return i + 3; } Are these two expressions the same? bind( &foo, _1 ); _1 + 3; Finally (for now!) - why is this wrong? struct A { string identity( string ) const; } a; vector<string> v; for_each( v.begin(), v.end(), cout << bind( &A::identity, a, _1 ) << '\n' ); which is intended to output the return value of A::identity() for each element of v, separated by newlines. Thanks in advance for any guidance! Rob. -- ACCU - Professionalism in programming - http://www.accu.org

5 4

[python] working with raw const pointers
by Gennadiy Rozental 11 Jun '08

11 Jun '08

Hi, In our system there are a lot of pointers to const objects flying around. I've got several problems in this regard. They can be exhibited by the following code snippet: a.cpp : class A{}; void boo1( A const* ) {} void boo2( A* ) {} A const* make_const_a() { return (A const*)0; } A* make_non_const_a() { return (A*)0; } std::vector<A const*> make_vec() { return std::vector<A const*>( 1 ); } .... class_<A,boost::noncopyable>( "A", bp::no_init ); class_<std::vector<A const*> >( "AVec", bp::no_init ) .def( vector_indexing_suite<std::vector<A const*> >() ) ; def( "boo", &boo1 ); def( "boo", &boo2 ); def( "make_const_a", &make_const_a, return_value_policy<reference_existing_object>() ); def( "make_non_const_a", &make_non_const_a, return_value_policy<reference_existing_object>() ); def( "make_vec", &make_v ec ); Problem I. Access to mutable func Following python statement mymodule.boo( mymodule.make_non_const_a() ) seems to call incorrect function boo Problem II. Vector fails completely Following python statements vec = pytoolkit.make_vec(); for e in vec: pass produce TypeError: No to_python (by-value) converter found for C++ type: class A const * Any advise? Gennadiy

1 0

Threaded version
by albert meyburgh 11 Jun '08

11 Jun '08

Is there a threaded version of some of the boost components? For example, calling find on a container should be easily threaded. I realize the user could also easily thread this, but it seems like a trivial thing to just add support for in boost itself.

3 2

[python] frame corruption in python -> c++ -> python scenario
by Gennadiy Rozental 10 Jun '08

10 Jun '08

Hi, I am experiencing strange issue I can't find solution for. Sorry I'll need a bit lengthy explanation to describe it. I am using boost python for both automation and embedding the same time. I wrote trivial unit test module (can't use standard one). It has function check like this: def check( val ): check_impl( val ) def check_impl( val ): ... print "Error at line " + str(sys._getframe(2).f_lineno+1) ... ... This supposedly should produce error line location. And it does. Sometimes. test1.py: ... 8> check( False ) produces: Error in line 8: ... I've noticed though that in some cases line numbers are incorrect. I was able to narrow it down to the single function mymodule.foo() Before this function call line numbers are correct. After it incorrect. foo is a function implemented in c++ and exported using boost.python. I was able further to identify that the line at fault inside function foo implementation is the one invoking python function: void foo() { ... boost::python::object obj = ... obj(); ... } So. Finally the question: Is there way to fix/circumvent this somehow? Thanks, Gennadiy

1 0

boost::decimal ?
by Mårten Rånge 10 Jun '08

10 Jun '08

Is there some work been done on implementing a boost::decimal class? If there isn't my guess is that this would be very useful to C++ programmers out there if boost could provide this (we sure would dance with joy!). I would like to help but frankly I lack the competence on how to implement a decimal class efficiently and with the robustness it needs. A decimal class would be very useful for ERP and Financial systems as in many cases of the typical customers work with the decimal system instead of the binary system. It's hard to motivate for the customers why: 1 -0.2 -0.2 -0.2 -0.2 -0.2 doesn't add up to _exactly_ 0 when using double (windows calc.exe had this problem many years ago and it attracted lot of gleeful comments, so gleeful calc.exe uses infinite precision these days to represent rational numbers). In addition many sums are intended to become 0 at the end (the debit and credit should be balanced) so cancellation errors like above actually are quite common. The key issue is that common numbers such as 0.1, 0.2, and so on can't be exactly represented in a double. http://www2.hursley.ibm.com/decimal/ -- Mårten

4 3

[serialization] Base64 padding in basic_text_oprimitive
by Vyacheslav E. Andrejev 10 Jun '08

10 Jun '08

Hello, Code that pads base64 output with '=' looks in basic_text_oprimitive.ipp like following: std::size_t padding = 2 - count % 3; if(padding > 1) *oi = '='; if(padding > 2) *oi = '='; It will give the following transformations of a few simple strings: "012" -> "MDEy=" "0123" -> "MDEyMw" "01234" -> "MDEyMzQ" "012345" -> "MDEyMzQ1=" Which violates the principle of the base 64 that the encoded output length is multiple of 4 bytes. Right output for the samples above should be: "012" -> "MDEy" "0123" -> "MDEyMw==" "01234" -> "MDEyMzQ=" "012345" -> "MDEyMzQ1" The problem with the code above is that the condition (padding > 2) is never satisfied. I think that the proper code should look like std::size_t padding = 2 - count % 3; if (padding < 2) { *oi = '='; if (padding > 0) *oi = '='; } -- -- Vyacheslav Andrejev -- System Architect, Optech International, Inc.

2 3

[serialization] implementing class_name_optional_type
by Esteve Fernandez 10 Jun '08

10 Jun '08

Hi all, I'm working on the "YAML archives for Boost.Serialization" GSoC project and I've already implemented a working output archive. However, since YAML requires the class name to be always serialized, I had to implement the serialization of a new type called class_name_optional_type in basic_oarchive.cpp, which lets the archive decide if class names should always be written. It was discussed in the past [1], but never implemented, AFAIK. Cheers. PS: should I send the patch to this list or is it better to create a new ticket? 1 - http://lists.boost.org/boost-users/2006/06/20319.php

2 9

Request: RDTSC
by dherring＠ll.mit.edu 10 Jun '08

10 Jun '08

The CPU timestamp counter is a high-resolution clock source useful for profiling code or controlling tight timing loops. AMD/Intel CPUs support this via the RDTSC opcode, and other CPUs often provide similar functionality. Apparently MS compilers support an __rdtsc() intrinsic, but I couldn't find one for gcc. The code at http://www-unix.mcs.anl.gov/~kazutomo/rdtsc.html seems to do a good job for gcc; it avoids a couple bugs in code found at other sites. Any possibility of a raw boost::rdtsc() or boost::readTSC()? Something that doesn't compile on unsupported architectures would be good. Other code can worry about whether this is an accurate time source[1]; I just want a portable way to access the raw counter itself. Thanks, Daniel [1] Search "rdtsc site:boost.org"

4 3

[shifted_ptr] "new shifted<T>"
by Phil Bouchard 10 Jun '08

10 Jun '08

Hi, Firstly after defining my own sh::pool allocator new doors opened on their own and now I am able to replace the "new_sh<>()" function call with a much more neat C++ approach with "new shifted<>()". For example instead of: shifted_ptr<char[9]> u = new_sh<char[9]>(); Now we can write: shifted_ptr<char[9]> u = new shifted<char[9]>(); This will allows us defining STL container allocators more easily because of the distinct steps the constructor and allocator are called; new_sh<>() was mixing them altogether. Secondly I was able to drastically clean up "class shifted<>" (was: owned<>) by unifying the construction of the member object with the construction of the class itself. This was necessary to use "new shifted<>()" adequately. Last but not least the library now takes advantage of the fast_pool_allocator for objects such as "struct set" and "numeric::interval<int>". FYI I am using "numeric::interval<int>" instead of "numeric::interval<void *>" because of a compilation failure with the latter. I am casting the pointers to an "int" meanwhile because there is no lost of information by doing so according to the standards. The files are both on Vault and the Sandbox and is nearly the official release. Documentation will follow soon for those who got no clue what I'm talking about: http://www.boost-consulting.com/vault/index.php?action=downloadfile&filenam… Thanks, -Phil

3 14

[regex] cygwin compile errors
by Emil Dotchevski 10 Jun '08

10 Jun '08

Please see the relevant part from my build log below. gcc.compile.c++ ../../../../../bin/lib/re_0_02_0/impl/test/header-reno_config~pimpl~h.test/gcc-3.4.4/debug/link-static/header-reno_config~pimpl~h.o In file included from /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_traits.hpp:35, from /cygdrive/c/code/lib/boost-trunk/boost/regex/regex_traits.hpp:27, from /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:39, from /cygdrive/c/code/lib/boost-trunk/boost/regex.hpp:31, from /cygdrive/c/code/lib/re_0_02_0/re/reno_config.pimpl.h:10, from header-test.cpp:4: /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_traits_defaults.hpp: In function `ptrdiff_t boost::re_detail::global_length(const charT*) [with charT = wchar_t]': /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_traits_defaults.hpp:234: error: `wcslen' is not a member of `std' In file included from /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_traits.hpp:44, from /cygdrive/c/code/lib/boost-trunk/boost/regex/regex_traits.hpp:27, from /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:39, from /cygdrive/c/code/lib/boost-trunk/boost/regex.hpp:31, from /cygdrive/c/code/lib/re_0_02_0/re/reno_config.pimpl.h:10, from header-test.cpp:4: /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp: At global scope: /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp:104: error: ISO C++ forbids declaration of `wstring' with no type /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp:104: error: expected `;' before "string_type" /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp:122: error: `string_type' does not name a type /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp:123: error: `string_type' does not name a type /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp:126: error: `string_type' does not name a type /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp: In static member function `static size_t boost::c_regex_traits<wchar_t>::length(const wchar_t*)': /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp:110: error: `wcslen' is not a member of `std' /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp: In member function `wchar_t boost::c_regex_traits<wchar_t>::translate_nocase(wchar_t) const': /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/c_regex_traits.hpp:119: error: `towlower' is not a member of `std' In file included from /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:76, from /cygdrive/c/code/lib/boost-trunk/boost/regex.hpp:31, from /cygdrive/c/code/lib/re_0_02_0/re/reno_config.pimpl.h:10, from header-test.cpp:4: /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/sub_match.hpp: At global scope: /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/sub_match.hpp:186: error: `std::wstring' has not been declared /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/sub_match.hpp:186: error: `const_iterator' was not declared in this scope /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/sub_match.hpp:186: error: template argument 1 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/sub_match.hpp:186: error: ISO C++ forbids declaration of `wssub_match' with no type In file included from /cygdrive/c/code/lib/boost-trunk/boost/regex.hpp:31, from /cygdrive/c/code/lib/re_0_02_0/re/reno_config.pimpl.h:10, from header-test.cpp:4: /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:140: error: `std::wstring' has not been declared /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:140: error: `const_iterator' was not declared in this scope /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:140: error: template argument 1 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:140: error: template argument 2 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:140: error: ISO C++ forbids declaration of `wsmatch' with no type In file included from /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:151, from /cygdrive/c/code/lib/boost-trunk/boost/regex.hpp:31, from /cygdrive/c/code/lib/re_0_02_0/re/reno_config.pimpl.h:10, from header-test.cpp:4: /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_iterator.hpp:172: error: `std::wstring' has not been declared /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_iterator.hpp:172: error: `const_iterator' was not declared in this scope /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_iterator.hpp:172: error: template argument 1 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_iterator.hpp:172: error: template argument 2 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_iterator.hpp:172: error: template argument 3 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_iterator.hpp:172: error: ISO C++ forbids declaration of `wsregex_iterator' with no type In file included from /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex.hpp:154, from /cygdrive/c/code/lib/boost-trunk/boost/regex.hpp:31, from /cygdrive/c/code/lib/re_0_02_0/re/reno_config.pimpl.h:10, from header-test.cpp:4: /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_token_iterator.hpp:286: error: `std::wstring' has not been declared /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_token_iterator.hpp:286: error: `const_iterator' was not declared in this scope /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_token_iterator.hpp:286: error: template argument 1 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_token_iterator.hpp:286: error: template argument 2 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_token_iterator.hpp:286: error: template argument 3 is invalid /cygdrive/c/code/lib/boost-trunk/boost/regex/v4/regex_token_iterator.hpp:286: error: ISO C++ forbids declaration of `wsregex_token_iterator' with no type Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode

1 1