November 2006 - Boost-users - lists.preview.boost.org

Boost:ASIO mailing list/group
by Stas 10 Nov '06

10 Nov '06

What is a right group/ mailing list ot ask ASIO related questions? Regards Stas

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locale for lexical_cast?
by Amin Kharchi 10 Nov '06

10 Nov '06

Hello! Is it possible to set a locale for the lexical_cast? It looks like that it is only possible to convert english/us numbers to a string? Example: float a = boost::lexical_cast<float>("12,3"); This would be in english 12.3. But I get a bad_cast exception for german numbers. A locale would be very helpful. Best regards Amin Kharchi

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Lambda, how difficult should it be?
by Martin Young 10 Nov '06

10 Nov '06

Hi, I've just started trying to use the Boost lambda library and I'm finding that I can't get anything much to work how I'd expect. I've read the docs and I'm none the wiser. I'm running on Cygwin using GCC 3.4.4 if that makes any difference. My problem is pretty nebulous - I can't get the non-workingness nailed down a specific issue - whenever I try something different I get several screenfulls of different error messages. So, previously I had a alot of code in the form below which performs linear searches of a vector. Clearly this is not the Right Thing, especially as I will want to change the vectors to different containers at a later point. typedef struct { int a; void* b; } foo; vector<foo*>* v = buildAndPopulateVector(); for( int i=0, iL=v->size(); i<iL; i++ ) { foo* thisFoo = (*v)[i]; if( thisFoo->a == 0 ) { thisFoo->a = 1; *(int*)(thisFoo->b) = 42; } } Instead, I'd like to use the for_each algorithm to iterate over the contents of the vector like this: foreach( v->begin(), b->end(), ### ) Where the ### would normally be a function pointer (or relative thereof). I'd like to use lambda so I can put my code inline. At first I thought I could do something like: foreach( v->being(), b->end(), if_then( _1->a == 0, ( _1->a = 1, *(int*)(_1->b) = 42 ) ) I quickly discovered that the placeholders don't work like that and a pile of bind and/or ->* operators are required to extract any interesting information. I think I've got this bit sorted now though. What I'm getting stuck on now is constructing a working version of the if/then construct. The condition expression seems okay... if_then( bind(&foo::a,_1)==0, but I just can't get the "body" part to compile. I have to enclose it in round brackets so it appears as one expression to the compiler, but then it's not a lambda expression so I need to wrap it in something to make it a lambda. I should then pass _1 in as the single parameter of my new nested lambda because the previous _1 won't be in scope anymore - is this right? Is there another (better) way to include multiple expressions in an if_then construct without making a nested lambda and thus losing the bindings from the original lambda? What should I wrap my expression in to make it a unary lambda into which I can pass _1 from the main lambda? It's not getting automatically picked up as a lambda expression because the use of _1 is in the middle of one of the comma separated sub exprssions. Can I even pass _1 into a nested lambda like that or does it need massaging first? I've found dealing with the placeholders to be very painful so far... Are there any examples of this kind of thing anywhere? All the examples I've found are incomplete or for very trivial cases, or have not been answered. Even the "Beyond the std lib/boost" book has only very simple examples and esoteric gotchas. It seems to me this ought to be a very simple thing - am I going about it in the wrong way? I've had a good Google and a read through this list's archives and there seems to be very little discussion about the lambda library. Is it moribund or am I the only person who can't make it work? Sorry for all the rather vague questions and thanks for any pointers. -Martin.

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binary_to_base64 example
by Kervin L. Pierre 10 Nov '06

10 Nov '06

Hello, Does someone have an example of how to use the base64_from_binary class to convert a 'char *' buffer to base64 text in a local buffer? I believe this is probably one of the simplest uses of the function but I can't make sense of the documentation. Best regards, Kervin

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no output from BOOST_MESSAGE
by Kervin L. Pierre 09 Nov '06

09 Nov '06

Hello, I wrote a few simple test cases using Boost test, and things seem to work ok except done of my BOOST_MESSAGE() calls output anything. If the predicate fails for BOOST_REQUIRE_MESSAGE() I do get the message outputed to the screen, but not for regular BOOST_MESSAGE() Is there a setting that I should tune to output BOOST_MESSAGE, or may suppress BOOST_MESSAGE? Also I saw in a message somewhere that these functions can output to other targets than the screen. If that is the case, how do I go about doing this? Best regards, Kervin

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[program_options] define precedent options?
by Rui Maciel 09 Nov '06

09 Nov '06

I've just discovered boost's program_options and at first glance it looked exactly what I was searching for, which was a easy to use library which was capable of handling the command line arguments parsing in a fast and efficient way. Unfortunately one of the things which I had my mind set to was the possibility of defining precedent options. To put it in other words, enable the parser to accept some options only if they were casted in a particular order and complain if that order wasn't respected. For example, accepting something like: app --add --file but complain if the arguments are like: app --file --add or app --add One other thing that I was hoping that boost's program_options was capable of handling was some sort of semantic interpretation according to the option's orders. Take this case for example: app --add --file --remove --file What I was hoping for was that program_options was capable of interpreting the first invocation of --file as relating to --add and the second invocation relating to --remove, instead of intepreting as two distinct invocations of --file. So, is it possible to accomplish that with boost's program_options? If so, could anyone be so kind to provide a simple example? Thanks in advance Rui Maciel -- Running Kubuntu 6.10 with KDE 3.5.5 and proud of it. jabber:rui_maciel@jabber.org

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efficient string to numeric conversion (and vice-versa)
by Maitre Bart 09 Nov '06

09 Nov '06

Is there a Boost lib that offers efficient string to numeric type conversion ? What about numeric to string conversion ?

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Ann: Alpha release of Boost.TR1-1.34
by John Maddock 09 Nov '06

09 Nov '06

I've placed an alpha release of the TR1 subset of Boost on the sourceforge download page: https://sourceforge.net/project/showfiles.php?group_id=7586&package_id=1893… Eventually, this package will track Boost-1.34 releases, but until that happens, I wanted to test the water and see how a subset like this would be received, and how best to organise it's packaging etc. So any feedback you have would be most welcome! The subset includes: TR1 Reference Wrappers Shared_ptr result_of mem_fn Function Object Binders Polymorphic Function Wrappers Type Traits Random Numbers Tuples Array Hash Functions Regular Expressions Complex Number Algorithms Enjoy! Regards, John Maddock.

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Add library to link against in Jamfile (building a Boost.python extension)
by Alexander Eisenhuth 09 Nov '06

09 Nov '06

Hello, I'm writing a Boost.python extension, that needs the Boost.thread library. I use the Jamfiles from Boost.python example (works, except of linking), and need to add the thread library. How can I do that? Jamfiele: ---------------------------------------------- # This is the top of our own project tree project-root ; # Include definitions needed for Python modules import python ; # ----- getting_started1 ------- # Declare a Python extension called getting_started1 extension getting_started1 : # sources getting_started1.cpp # requirements and dependencies for Boost.Python extensions <template>@boost/libs/python/build/extension ; ------------------------------------------------- Thanks a lot Regards Alexander

2 1

undefined reference to `boost::read_graphviz
by Teodora Miteva 09 Nov '06

09 Nov '06

Hi, i got this problem when i tried to compile the graphviz.cpp: ------------------------- undefined reference to `boost::read_graphviz(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, boost::subgraph<boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, boost::property<boost::vertex_attribute_t, std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, boost::no_property>, boost::property<boost::edge_attribute_t, std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, boost::property<boost::edge_index_t, int, boost::no_property> >, boost::property<boost::graph_graph_attribute_t, std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, boost::property<boost::graph_vertex_attribute_t, std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, boost::property<boost::graph_edge_attribute_t, std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, boost::property<boost::graph_name_t, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::no_property> > > >, boost::listS> >&)' --------------------------------- i saw the explanation and some previous mails but still i have the problem... i built the lib libbgl-viz.a following the instructions ( http://www.cs.brown.edu/~jwicks/boost/libs/graph/doc/read-graphviz.html<http://www.cs.brown.edu/%7Ejwicks/boost/libs/graph/doc/read-graphviz.html>) , but still doesnt work ......... could you tell me what i could i do to salve it? thanks best teodora

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