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

~optional<int> generates unnessesary code
by Hite, Christopher 25 Jan '12

25 Jan '12

The problem is that m_initialized is checked and set during deconstruction. This generates a bunch of useless code for types with trivial deconstruction: if(m_initialized){ // do nothing m_initialized = false; } The code is more than useless since it contains a branch. In my case I've got a big object I would expect to die without peep, branching and writing to memory for no reason. The steps below show what gcc 4.6.0 generates. You'd expect the function to do nothing. Boost optional has no obligation to maintain state during deconstruction (otherwise you'd need states for deconstructing,constructing). It's not responsible for the bytes left behind after deconstruction. By the way boost::variant does do this correctly. Chris ------------------ #include <boost/optional.hpp> typedef boost::optional<int> optional_int; void deconstruct_boost_optional(optional_int& o){ o.~optional_int(); } ------------------ objdump -f -d -C -l boost_optional_deconstruction.o |c++filt 00000000 <deconstruct_boost_optional(boost::optional<int>&)>: deconstruct_boost_optional(boost::optional<int>&)(): /home/eh2hite/chris/src_root/src/test/boost_optional_deconstruction.cpp:5 0: 8b 44 24 04 mov 0x4(%esp),%eax boost::optional_detail::optional_base<int>::destroy()(): /usr/local/include/boost/optional/optional.hpp:407 4: 80 38 00 cmpb $0x0,(%eax) 7: 74 03 je c <deconstruct_boost_optional(boost::optional<int>&)+0xc> boost::optional_detail::optional_base<int>::destroy_impl(mpl_::bool_<false>)(): /usr/local/include/boost/optional/optional.hpp:434 9: c6 00 00 movb $0x0,(%eax) c: f3 c3 repz ret

2 2

BGL defining my own iterator?
by Anders Wallin 24 Jan '12

24 Jan '12

Hi all, For traversing the faces of a planar BGL graph I store 'next' pointers in a bundled property for each edge. I can go round a face of the graph like this: BGLGraph g; edge_descriptor current,start; // initialize these! do { // do something with current current=g[current].next; } while(current!=start); Now I was thinking that a lot of 'boilerplate' code would be eliminated if I could do these loops with BOOST_FOREACH. Following the tutorial for iterator_facade I am trying something like this: https://github.com/aewallin/sandbox/blob/master/bgl_iterator/main.cpp However as commented in the code it doesn't quite work. I get either no iterations, one iteration, or all but one edge. Also, holding a pointer to an edge_descriptor in the iterator class doesn't strike me as very elegant, could I store an edge_descriptor directly? suggestions? thanks, AW

2 3

Boost MSM: No transition from submachine to external state
by stetkas 24 Jan '12

24 Jan '12

Using the following example as a template: http://svn.boost.org/svn/boost/trunk/libs/msm/doc/HTML/examples/CompositeTu… http://svn.boost.org/svn/boost/trunk/libs/msm/doc/HTML/examples/CompositeTu… I am trying to create a state machine that consists of an alarm state and a composite state (submachine). When an alarm event is posted while in the composite state, the state machine is supposed to transition to the Alarm state; however, the machine complains that no transition from the composite state on the alarm event exists. This is similar to the example where the player is in playing and a stop event is received. Below is a dumbed-down version of my state machine: http://boost.2283326.n4.nabble.com/file/n4300991/StateMachine.gif Here is the implementation: Here is the output: See anything that could be causing my problem? -- View this message in context: http://boost.2283326.n4.nabble.com/Boost-MSM-No-transition-from-submachine-… Sent from the Boost - Users mailing list archive at Nabble.com.

2 6

Simple example program builds but hangs when I run it. (Ubuntu).
by vincegata 24 Jan '12

24 Jan '12

Hello, I run Ubuntu 11.04. I downloaded Boost 1.48.0, then I followed the instructions from Getting Started on Unix variants to build the libraries into /usr/local/include and /usr/local/lib. Now, I build the Simple example program without any errors, however when I run the program it just hangs indefinitely on std::for_each() line. Could someone help me with this please? $: g++ -g -lboost_filesystem main.cpp #include <boost/lambda/lambda.hpp> #include <iostream> #include <iterator> #include <algorithm> int main() { using namespace boost::lambda; typedef std::istream_iterator<int> in; std::for_each(in(std::cin), in(), std::cout << (_1 * 3) << " " ); int stop = 1; }

3 3

Re: [Boost-users] Need help with Errors in boost MPL, tutorials
by Linh Ha 24 Jan '12

24 Jan '12

> Just on a first glance, looks like you're mistaking ::_1 (placeholder from > Boost.Bind) for boost::mpl::_1 (placeholder from Boost.MPL). They're > incompatible; try using the latter...? > > - Jeff Thanks, Jeff ! It works. But then my next question is why they are different and somehow incompatible even-though are both placeholders. Why we keep two different place holder if they do exactly a same functionality.

2 1

license
by Kraus Philipp 24 Jan '12

24 Jan '12

Hello, I would like to create a PHP plugin that uses the Boost UBlas datatypes. The plugin will be use the GPLv3 license. Can I use the bcp utility to extract the UBlas structures and can I include them into my plugin without any license problems? The plugin should store all needed parts into its own directory. Thanks Phil

1 0

Need help with Errors in boost MPL tutorials
by Linh Ha 24 Jan '12

24 Jan '12

Dear all, I try to learn Meta-programing but i got stuck with lambda meta-function and place holder. I try to compile very simple program #include <boost/bind.hpp> #include <boost/mpl/lambda.hpp> #include <boost/type_traits.hpp> template <class F, class X> struct twice : F::template apply<typename F::template apply<X>::type > { }; template <class X> struct two_pointers : twice<typename boost::mpl::lambda<boost::add_pointer<_1> >::type, X> {}; int main(int argc, char** argv) { return 0; } It is from the boost tutorial http://www.boost.org/doc/libs/1_48_0/libs/mpl/doc/tutorial/the-lambda-metaf… . But it can not be complied. The error messages are main.cpp:21: error: type/value mismatch at argument 1 in template parameter list for ‘template<class T> struct boost::add_pointer’ main.cpp:21: error: expected a type, got ‘<unnamed>::_1’ main.cpp:21: error: template argument 1 is invalid main.cpp:21: error: template argument 3 is invalid main.cpp:21: error: template argument 1 is invalid main.cpp:22: error: expected ‘::’ before ‘{’ token main.cpp:22: error: expected class-name before ‘{’ token I use g++ (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5 I have no idea what happened. Any inside would be appreciated. It is important I think since lambda is used all over place with MPL. Thanks, Linh Ha

2 1

[Spirit][karma] Generating Pascal string like output
by Olaf Meeuwissen 23 Jan '12

23 Jan '12

Hi all, While I had no trouble getting the parsing part for this to work, I'm stuck on the generator part. Specifically, I'm stuck on getting the size into the output. The goal is a rule that takes a std::vector<byte> and outputs it in such a way that it is preceded by its size (in a custom encoding) and padded by zeroes to align on a four byte boundary. I want to reuse this rule in several other rules and prefer to break it up into smaller pieces. A minimalistic example of what I have come up with so far is attached. What I can't seem figure out how to get at and store the vector's size in pascal_string_size_. There also seem to be problems with refering to the stored size_ in pascal_string_payload_ and pascal_string_padding_ that I don't understand. Note that the signed/unsigned distinction is on purpose. I am aware of the side effects of assigning to size_ and that that is not threadsafe. Any help would be appreciated. Thanks in advance, -- Olaf Meeuwissen, LPIC-2 FLOSS Engineer -- AVASYS CORPORATION FSF Associate Member #1962 Help support software freedom http://www.fsf.org/jf?referrer=1962

2 4

grid_graph vertex properties
by David Doria 23 Jan '12

23 Jan '12

Since there is no VertexProperties template parameter on grid_graph, is it correct that you cannot use interior properties, but must use exterior properties? Thanks, David

2 5

Building boost_1_48_0 with specified version of msvc...
by JIA Pei 23 Jan '12

23 Jan '12

Hi, all: I strictly followed "Getting Started" on Boost documentation, although I'm using a Visual Studio 2008 Command Prompt, it seems it always produce all boost libraries using VC10. Is it possible to produce boost libraries built by VC9? Please help...Thank you very much. Best Regards Pei -- Pei JIA Email: jp4work(a)gmail.com cell: +1 604-362-5816 Welcome to Vision Open http://www.visionopen.com

2 1