January 2012 - Boost-users - lists.preview.boost.org

Compile error when using program_options and lambda expression
by Jens Auer 23 Jan '12

23 Jan '12

Hi, I ran into a problem when I was replacing boost::bind expressions with lambda expressions. I could boil down the problem to the following code: #include <boost/program_options.hpp> template<typename T> void f(T t) {} void g() { using namespace boost::program_options; // each of the following lines produces the error: // Error 1 error C2871: 'validators' : a namespace with this name does not exist // Error 2 error C2871: 'program_options' : a namespace with this name does not exist f([]() {} ); auto x = []() {}; } When I try to compile this on my Microsoft Visual Studio 2010 using our Boost 1.45 library, I get a compiler errors: Error 1 error C2871: 'validators' : a namespace with this name does not exist Error 2 error C2871: 'program_options' : a namespace with this name does not exist To me, it looks like a compiler problem but I want to make sure that I am not running into a known issue in the boost libraries. I have search the bug database, but I have not found any issues like this one. It would be nice if someone could double-check this on another platform and boost version. If it is a compiler bug, I would then file a bug report to MS. Best regards, Jens

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FTP Server class
by Christer Borgqvist 23 Jan '12

23 Jan '12

Hello all, Im trying to make a multi threaded FTP Server class using boost asio. When in passiv mode, create a server listen on the data port and wait for a connection from the client, that thread need som event to trigg the thread to start send the file after the command RETR have received. is there some one that can help me. /Christer

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[units] Question about user-defined value types
by W Z 23 Jan '12

23 Jan '12

Hi, I am using boost units library for a project in which I need to define quantities using rational numbers. I have a rational number class but am having trouble integrating it with units library. There seems to be a lot of places where the units library implementation assumes that the conversion values are expressed as double type. Is there a good way to get around this to make units library support rational numbers? Thanks, WZ

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Iterating over vertices in a specific region in a graph
by David Doria 22 Jan '12

22 Jan '12

If I manually create a grid graph in BGL (using adjacency_list, not grid_graph), is there a way to iterate over vertices in a specified rectangular region? Say I make a 100x100 grid graph, how would I iterate over the the center 5x5 vertices? Thanks, David

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Multicast sender
by Carlos Guimarães 22 Jan '12

22 Jan '12

Hi, Is there any portable way (by using boost) to send multicast messages through all network interfaces available on the host? I have managed to do it by setting outbound_interface option on the socket. However, how can I know which if_index are available? Also, it only works for IPv6. If I set a IPv4 address it always use the same interface. Any suggestion? Next is the code I'm using: // DATA HERE... ip::udp::socket sock(io); sock.open(ip::udp::v6()); // Set socket flags sock.set_option(boost::asio::socket_base::reuse_address(true)); if (strcmp(dst_ip, "ff02::1") == 0) { boost::asio::socket_base::broadcast option(true); sock.set_option(option); } sock.bind(ip::udp::endpoint(ip::address_v6::any(), src_port)); for(int i = 1; i <= 5; i++) { try { sock.set_option(ip::multicast::outbound_interface(i)); sock.set_option(ip::multicast::enable_loopback(false)); ip::udp::endpoint ep(ip::address::from_string(dst_ip), dst_port); sock.async_send_to(boost::asio::buffer(sbuff, slen), ep, boost::bind((&send_handler), placeholders::error)); } catch(...) { return; } }

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[Units] Issue with user defined quantities
by Pieter B. 22 Jan '12

22 Jan '12

LS, I have some problems working with user defined quantities/units in combination with unitless quantities (such as the results of a sin() or cos() operations).Taking the example of the 'nautical mile', which is presented in the documentation: ---START CODE --- namespace nautical { struct length_base_unit : boost::units::base_unit<length_base_unit, length_dimension, 1> { static std::string name() { return "nautical mile"; } static std::string symbol() { return "nmi"; } }; typedef boost::units::make_system<length_base_unit>::type system; typedef unit<length_dimension,system> length; static const length mile,miles; } BOOST_UNITS_DEFINE_CONVERSION_FACTOR(nautical::length_base_unit, boost::units::si::meter_base_unit, double, 1.852e3); ---END CODE --- The following does not compile: ---START CODE --- typedef quantity<boost::units::si::plane_angle> TAngleInRad; typedef boost::units::quantity<nautical::length> TNauticalDistanceInNMI; TNauticalDistanceInNMI NauticalDistanceInNMI; TNauticalDistanceInNMI SumNauticalDistanceInNMI = NauticalDistanceInNMI + NauticalDistanceInNMI; // OK TNauticalDistanceInNMI ScaledSumNauticalDistanceInNMI = NauticalDistanceInNMI + NauticalDistanceInNMI*sin(AngleInRad); // Last line does not compile due to lack of a suitable operator+ ---END CODE --- It does work correctly when using the 'nautical mile' as it has been defined in the library itself in "nautical_mile.hpp" (as a scaled base unit related to the si::meter): ---START CODE --- namespace metric { typedef scaled_base_unit<boost::units::si::meter_base_unit, scale<1852, static_rational<1> > > nautical_mile_base_unit; } // definition of the nautical mile from "nautical_mile.hpp" typedef boost::units::metric::nautical_mile_base_unit::unit_type nautical_mile_unit; typedef quantity<nautical_mile_unit> TNauticalDistanceInNMI; ---END CODE --- However, I don't think I can specify my user-defined units/quantities in this manner as they use a scale factor represented by an arbitrary floating point value. My perception is that the example of the documentation does not work due to the mixing of quantities from the si system (the sin() returns a dimensionless quantity in that system) with user-defined quantities in another ('nautical') system, while the 'nautical mile' from 'nautical_mile.hpp' is a scaled version of the si::meter and thus defined within the realms of the si::system - but please correct me if I am wrong here. My problem can thus be summarized as follows: - the solution from the documentation does not compile - the solution from 'nautical_mile.hpp' uses a scaled base unit which is limited to scaling factors of the form scale<Base,Exponent> and my question is therefore: how can I define my user-defined units/quantities in such a way that they allow the required operations while being related to base units by an arbitrary scale factor? Help would be highly appreciated, Pieter ------------------- Nautical mile version #1 (from the included nautical_mile.hpp): namespace metric { typedef scaled_base_unit<boost::units::si::meter_base_unit, scale<1852, static_rational<1> > > nautical_mile_base_unit; } template<> struct base_unit_info<metric::nautical_mile_base_unit> { static const char* name() { return("nautical mile"); } static const char* symbol() { return("nmi"); } }; typedef quantity<boost::units::si::plane_angle> TAngleInRad; typedef quantity<boost::units::si::length> TDistanceInM; typedef boost::units::metric::nautical_mile_base_unit::unit_type nautical_mile_unit; typedef quantity<nautical_mile_unit> TDistanceInNMI; typedef boost::units::quantity<nautical::length> TNauticalDistanceInNMI; # this is OK: TAngleInRad Angle(0.5*radians); TDistanceInNMI DistanceInNMI; TDistanceInNMI SumDistanceInNMI = DistanceInNMI + DistanceInNMI; TDistanceInNMI ScaledSumDistanceInNMI = DistanceInNMI + DistanceInNMI*sin(AngleInRad); TNauticalDistanceInNMI NauticalDistanceInNMI; TNauticalDistanceInNMI SumNauticalDistanceInNMI = NauticalDistanceInNMI + NauticalDistanceInNMI; TNauticalDistanceInNMI ScaledSum NauticalDistanceInNMI = NauticalDistanceInNMI + NauticalDistanceInNMI*sin(AngleInRad); // DOES NOT COMPILE for lack of a suitable operator+

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[phoenix] [cmath] lazy pow not working in boost 1.48
by alfC 22 Jan '12

22 Jan '12

Hi, Is this a bug in phoenix? the boost::phoenix::pow lazy function doesn't seem to work. My version is Boost 1.48 or maybe 1.49 (after svn update) -- Thanks, Alfredo #include<iostream> #include <boost/phoenix.hpp> #include <boost/phoenix/stl/cmath.hpp> using std::clog; using std::endl; int main(){ using namespace boost::phoenix::arg_names; clog << boost::phoenix::sin(arg1)(1.) << " " << std::sin(1.) << endl; // ok clog << boost::phoenix::pow(arg1, arg1)(2.) << " " << std::pow(2.,2.) << endl; // ^^^^------ error: no matching function for call to ‘pow(const boost::phoenix::expression::argument<1>::type&, double) return 0; }

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Why does boost thread copy a functor?
by Chris Cleeland 22 Jan '12

22 Jan '12

I had code similar to the following... Functor object: struct Task { operator()() { // thread main } smartfd p; }; Note that smartfd is a wrapper around a file descriptor. In its dtor it closes the fd. Then, elsewhere I set up an instance of Task and spawn it with boost::thread... Task t; t.p = // open file descriptor boost::thread thr(t); The spawned thread gets an instance of Task, but it's not the same instance as from the main. What is the rationale? -- Chris Cleeland

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Vote Boost Up for SourceForge Project of the Month
by Dave Abrahams 20 Jan '12

20 Jan '12

Folks, I was just informed that Boost is a top contender for SourceForge's February Project Of The Month. The vote is happening on TwtPoll, here: http://twtpoll.com/7vt4lq It's pretty close, so if you could vote Boost up, it could be good for our profile and our future. Thanks! -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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Re: [Boost-users] Is there any functions that convert Chrono's time_point and duration to their Ptime equivalents?
by Iron Bug 20 Jan '12

20 Jan '12

I found such functions somewhere in boost's sandbox, in chrono development. There're some templates that can be used as examples and adopted for all such conversions. I think, they will be added to chrono, possibly. Look here: http://svn.boost.org/svn/boost/sandbox/chrono/boost/conversion/boost/

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