June 2011 - Boost-users - lists.boost.org

Using function operator in lambda expression
by Alexander Khomyak 03 Jun '11

03 Jun '11

Hi. According lambda documentation <http://www.boost.org/doc/libs/1_38_0/doc/html/lambda/le_in_details.html #lambda.operator_expressions> there is a possibility to use function call operator in lambda expression. But I can't compile following code using MS Visual Studio 2003.NET compiler: #include <boost/lambda/lambda.hpp> using namespace boost::lambda; int foo(int i) { return i; } Somewhere in main function: (_1(1))(foo); Could you give me example of using function call operator in lambda expression? In advance thank you very much.

3 2

boost::assign::list_of and C++0x
by Travis Gockel 03 Jun '11

03 Jun '11

I'm moving a fairly large project over to C++0x, since it is about to be published (crosses fingers) and we need to stay up with the times. In this project, we use the wonderful boost::assign::list_of to assign collections (since initializer lists don't exist yet). We are using g++ 4.5.1 and Boost 1.46.1. When switching to C++0x, bits of code like this break: std::vector<int> vec; vec = boost::assign::list_of(1)(2)(3); with the following error: break_list_of.cpp:7:41: error: ambiguous overload for ‘operator=’ in ‘vec = ((boost::assign_detail::generic_list<int>*)boost::assign::list_of(const T&) [with T = int]().boost::assign_detail::generic_list<T>::operator() [with T = int, boost::assign_detail::generic_list<T> = boost::assign_detail::generic_list<int>, boost::assign_detail::generic_list<T>::Ty = int](((const boost::assign_detail::generic_list<int>::Ty&)((const boost::assign_detail::generic_list<int>::Ty*)(&2)))))->boost::assign_detail::generic_list<T>::operator() [with T = int, boost::assign_detail::generic_list<T> = boost::assign_detail::generic_list<int>, boost::assign_detail::generic_list<T>::Ty = int](((const boost::assign_detail::generic_list<int>::Ty&)((const boost::assign_detail::generic_list<int>::Ty*)(&3))))’ /usr/include/c++/4.5/bits/vector.tcc:156:5: note: candidates are: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = int, _Alloc = std::allocator<int>] /usr/include/c++/4.5/bits/stl_vector.h:336:7: note: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(std::vector<_Tp, _Alloc>&&) [with _Tp = int, _Alloc = std::allocator<int>, std::vector<_Tp, _Alloc> = std::vector<int>] /usr/include/c++/4.5/bits/stl_vector.h:357:7: note: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(std::initializer_list<_CharT>) [with _Tp = int, _Alloc = std::allocator<int>, std::vector<_Tp, _Alloc> = std::vector<int>] The problem is that there are now multiple ways to assign to vectors (and all the other collection types). Ideally, I would replace all usage of boost::assign::list_of with C++0x initializer lists, but, alas, I am lazy. Furthermore, I think I know how to fix this (see example below) and think the Boost community would benefit from having boost::assign::list_of work in C++0x and C++. template <typename T> struct is_initializer_list : boost::false_type { }; template <typename T> struct is_initializer_list<std::initializer_list<T> > : boost::true_type { }; template <typename T> struct wrapped_type { wrapped_type(const T& val) : _val(val) { } template <typename TOut, // use new support for default template arguments in functions typename TPhony = typename boost::disable_if<is_initializer_list<TOut> >::type > operator TOut() const { return _val; } private: T _val; }; I was wondering if anybody has solved this problem (or a similar one) already. I would patch it myself, but I only have g++ and clang to test it on. Also, there is a high probability that my solution is flawed in some way. Thanks for the help! And, as always, thanks for the wonderful library. -- - Travis Gockel

3 4

Re: [Boost-users] [range] cannot use lambda predicate in adaptor with certain algorithms
by Michel MORIN 03 Jun '11

03 Jun '11

Hi Daniel, Daniel Walker wrote: > At some point, BOOST_RESULT_OF_USE_DECLTYPE may be defined by default, > probably when there's enough user interest, so thanks for cc'ing me. > The reason it is currently not defined by default is that it is > possible that it could introduce breaking changes to some C++03 > function objects; e.g. if a function object defines result_type to be > some type other than the type of a call expression, then in C++03 > result_of would give the user-specified result_type rather than the > actual result type, whereas in C++0x result_of always gives the actual > result type. For example: > > #include <boost/type_traits.hpp> > #include <boost/utility/result_of.hpp> > > struct f { > typedef int result_type; > double operator()(double); > }; > > int main() > { > using namespace boost; > typedef result_of<f(double)>::type type; > #ifdef BOOST_RESULT_OF_USE_DECLTYPE > static_assert(is_same<type, double>::value, ""); > #else > static_assert(is_same<type, int>::value, ""); > #endif > } Thank you for explaining the problem. And yes, backward compatibility is always problematic. IMO, this use case is not the intended use of boost::result_of, so is it reasonable to deprecate this? And how about adding a "Note" that warns this kind of codes will break in the future to the documentation? Regards, Michel P.S. Eric just completed a patch for BOOST_NO_DECLTYPE_N3276: http://permalink.gmane.org/gmane.comp.lib.boost.devel/219979

2 2

[asio] custom baud rates?
by Frank 02 Jun '11

02 Jun '11

Hello, I need to use a 500000 baud rate with the serial port. When I attempt to set this baud rate I get an EINVALID. How can I use custom baud rates with asio? I'm running on Mac OS X 10.6. Note that I can use the 500000 baud rate just fine on windows running .Net (i.e. not asio). Thanks, Frank

1 0

Solaris sparc always producing 32bit libs
by Manoj Jangid 02 Jun '11

02 Jun '11

Hi I am trying to build boost in Solaris sparc machine, its always produce 32bit libs. Here is the commend I am using ./bjam --build-dir=$HOME/boost_rel64 --with-thread --with-system --with-date_time --with-random link=shared --stagedir=$HOME/boost_rel64 --layout=tagged link=shared variant=release address-model=64 my compiler version CC -V CC: Sun C++ 5.8 2005/10/13 uname -a SunOS mjnew 5.10 Generic_118833-03 sun4u sparc SUNW,Sun-Fire-V890 How do I produce 64bit libs? Thanks

1 0

Query about warning messages
by Leo Carreon 01 Jun '11

01 Jun '11

Hi, When I built Boost 1.45.0, 1.46.0 and 1.46.1 on Solaris, I noticed that there were a lot of warning messages. Are these warning messages benign? Regards, Leo

1 0

Query on Boost 1.47.0
by Leo Carreon 01 Jun '11

01 Jun '11

Hi, Is support for stdcxx4 going to be included in Boost 1.47.0 for Solaris? If not, can you please include it. Regards, Leo

1 0

[iostreams] Auto link iostreams but not external dependencies
by Sebastian Karlsson 01 Jun '11

01 Jun '11

It seems to be impossible to auto link iostreams but not external dependencies unless you want to link using defines. This matters to us as we use premake where one can reference a project dependency by its premake project id for automatic handling of linking on that end, and that feature does not work through defines.

1 0

How to download latest Boost?
by The Novice Coder 01 Jun '11

01 Jun '11

I tried following the directions on the web site - http://www.boost.org/users/download/ Which states the following: > ACCESSING THE BOOST SUBVERSION REPOSITORY > > The Subversion repository can be accessed in several ways: > > * Anonymous, read-only access to the Boost Subversion repository is available at http://svn.boost.org/svn/boost [1]. To access the current Boost development code, for instance, one would check out from http://svn.boost.org/svn/boost/trunk [2]. For example, using the command-line svn, one might use: > > svn co http://svn.boost.org/svn/boost/trunk [3] boost-trunk > On Windows, TortoiseSVN [4] provides an > easy-to-use, graphical interface to Subversion. However it didn't work. It started to, it got part way through the download then asked for a password. Now that's all it does: > ~/boost $ svn co http://svn.boost.org/svn/boost/trunk boost-trunk > Authentication realm: Boost SVN repository Subversion Access > Password for 'user': > > svn: OPTIONS of 'http://svn.boost.org/svn/boost/trunk': authorization failed: Could not authenticate to server: rejected Basic challenge (http://svn.boost.org) What password is expected, and why is it not listed on the web page in the download instructions? http://www.boost.org/users/download/ Links: ------ [1] http://svn.boost.org/svn/boost [2] http://svn.boost.org/svn/boost/trunk [3] http://svn.boost.org/svn/boost/trunk [4] http://tortoisesvn.tigris.org/

1 0

Issue with Multicast
by Andre Zeps 01 Jun '11

01 Jun '11

Hi, I've found some issue with the multicast examples of boost asio. It seems that the first received package after starting the receiver is always ignored. Is this a boost problem ?

1 0