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

Why don't smart pointers have the same semantics as plain pointers?
by Pierre THIERRY 17 Jan '06

17 Jan '06

I use more and more BOOST smart pointers instead of plain pointers in my C++ code, and it is incredible how it saves time and prevent bugs! But I was wondering why one couldn't just change the type of a pointer a keep all code as it is, instead of having to change affectation to reset(), for example. E.g., the following code: Foo* ptr_foo; ptr_foo = new Foo; Has now to be changed to: shared_ptr<Foo> ptr_foo; ptr_foo.reset(new Foo); But I'd like it to be: shared_ptr<Foo> ptr_foo; ptr_foo = new Foo; Is there a problem to have shared_ptr<T>::operator=(T*)? Curiously, Nowhere man -- nowhere.man(a)levallois.eu.org OpenPGP 0xD9D50D8A

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boost::spirit block of C++ code
by elviin 17 Jan '06

17 Jan '06

I created this parser and it is working for me except the detail: //------------------ //the body of the block cpp_code_block_text = *(anychar_p-ch_p('{')-ch_p('}')); //the code begins with '{' cpp_code_block_begin_p = ch_p('{'); //the code ends with '}' cpp_code_block_end_p = ch_p('}'); //parser: cpp_code_block_p = cpp_code_block_begin_p >> repeat_p (0, 100)[(cpp_code_block_p|cpp_code_block_text)] >> cpp_code_block_end_p; ---------------------- Here is the text I'm using for tests: {asas {bbbbbb bbb b b { asa}bb bbb b bb } as {aaaa} {aaaacc} asasa {} aaa } And the problem is in repeat_p (0, 100). I'd like to use * instead but it does not work for me because the parser runs forever. 100 means the number of blocks cpp_code_block_p or cpp_code_block_text. Where is the problem? Thank you very much for reply.

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Boost has a function to const-qualify?
by MB 16 Jan '06

16 Jan '06

Hi, Does boost has anything like : template< class T > inline const T& const_(const T& x) { return x; } I guess that boost::cref is different... Regards, MB p-stade.sourceforge.net

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lvalue error
by Fredrik Wikström 16 Jan '06

16 Jan '06

Hi! I have a polymorphic class in c++ like: class Example { public: void do_something() = 0; void do_something_more {} } This is wrap like: #include <boost/python.hpp> using namespace boost::python; struct ExampleWrap : Example, wrapper<Example> { void do_something() { this->get_override("do_something")(); } }; and finally: BOOST_PYTHON_MODULE(test) { class_<ExampleWrap, boost::noncopyable>("Example") .def("do_something", pure_virtual(&Window::do_something)) .def("do_something_more", &Window::do_something_more) ; } This compiles fine, the python code that work looks like: class Example(test.Example) def do_something(self): ...some code... e = Example() e.do_something_more() The python code that doesn't work looks like: class Example(test.Example) def __init__(self): ..some code... def do_something(self): ...some code... e = Example() e.do_something_more() This generates the error: e.do_something_more() Boost.Python.ArgumentError: Python argument types in Example.do_something_more(Example) did not match C++ signature: do_something_more(Example {lvalue}) How can I fix this? I really need to define a constructor in python class that inherit from the c++ Example class. /Fredrik ----------------------------------------------- This mail was sent through www.lulea.cc

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Re: [Boost-users] Pyste/Pyplusplus/Boost documentation problems
by Drumheller, Michael 16 Jan '06

16 Jan '06

(Sorry for the lateness of this response to the notes of Dave Abrahams, Tony Kirke, Stefan Seefeld & Roman Yakovenko.) I asked whether anyone out there gets anything done using Boost.Python *without* using Pyste or pyplusplus, and I said >> It does not seem like a practical thing to do--but maybe I'm missing >> something...? Dave replied: >> Why do you say that? Similarly, Stefan replied: >> I have been using boost.python for a number of projects but I never >> used pyste for any of them. What's wrong with that ? What do you >> think *I* am missing ? (By the way, Stefan: Does your above remark mean you have not tried Pyste, or you tried it and decided to use Boost.Python directly?) To answer your questions: Maybe I *would* just be using Boost.Python directly if I had spent a more time getting used to it at the beginning. But I found that getting even the simplest class hierarchies with virtual functions to work was an error-prone pain in the rear, not to mention a lot of typing. I discovered Pyste at the same time, and tried it, and looked at its output and said, "Wow, I'm glad I didn't have to write all that myself. Who has time for that?" I mean, Pyste's output is by definition a mechanical transformation of my C++ header files--why would I want to perform such a transformation by hand? That's how I got hooked on Pyste. It occurs to me that maybe the reason you do not seem bothered by writing Boost.Python code manually is that you're doing it "minimally," i.e., you're exposing that part (and only that part) of your C++ interface that really needs to be exposed at the Python level. I think I need to revisit my code with this in mind, and I will do that. And/or maybe I can/should just use Pyste as a "bootstrap" mechanism--to generate the *first version* of my Boost.python files, but maintain them manually thereafter. Roman indicates, with this message, <<http://mail.python.org/pipermail/c++-sig/2006-January/010030.html>>, that this is what a lot of people do, but I'm not sure it has really been substantiated. Of course, there is at least one excellent reason for writing Boost.Python wrappers by hand: The longer your tool chain, the more complicated your life. A longer tool chain (i.e., a tool chain with Pyste *and* GCCXML in it) makes it harder for me to sell the hybrid Python/C++ approach to my organization--or even to myself. It is not clear to me what the right balance is between automatic Boost.Python code generation & tool-chain complexity. I'm sure it is project-dependent. I suppose my main suggestion is that the Boost documentation might provide more guidance in making this trade-off. (There is a link to Pyste and that's it. There is no discussion about trade-off or how to address it.) Thanks, Michael

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date_duartion <-> months
by Oliver.Kowalke＠infineon.com 16 Jan '06

16 Jan '06

Hello, how can I extract the months from a date_duration? Thx, Oliver

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Cast boost::shared_array<T> to boost::shared_array<const T>?
by Joseph Turian 16 Jan '06

16 Jan '06

Is it possible to cast boost::shared_array<T> to boost::shared_array<const T>? If so, how can I do that? Thanks, Joseph -- http://www.cs.nyu.edu/~turian/

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shared_ptr with template class
by Pooyan McSporran 15 Jan '06

15 Jan '06

I'm in the process of converting a large pile of legacy code which uses raw pointers to instead use boost::shared_ptr exclusively. I've got almost all of it converted and working, with one exception. Normally, given a type of Foo I define a smart pointer FooPtr, for example: class Foo; typedef boost::shared_ptr<Foo> FooPtr; But some code uses a templated type, for example: template<typename T> class Foo; Ideally, I'd use a templated typedef, for example: template<typename T> typedef boost::shared_ptr<Foo<T> > FooTPtr; but that is currently illegal in C++. Has anyone found a clean workaround? For now, I'll just do without a typedef in this case :)

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Detect ICU support in Regex?
by Joseph Turian 15 Jan '06

15 Jan '06

Hi, A program I'm writing requires that the Boost Regex library was compiled with ICU support. How can I determine at configure/compile time whether the Regex library has ICU support? I'd like to prevent the user from shooting him/herself in the foot. Joseph -- http://www.cs.nyu.edu/~turian/

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Pyste/Pyplusplus/Boost documentation problems
by Drumheller, Michael 15 Jan '06

15 Jan '06

This gmane entry <<http://article.gmane.org/gmane.comp.python.c++/9049/match=pyplusplus+m ature>> says, among other things, the following """If you can, use pyplusplus over pyste. I say that for ALL users of pyste, pyplusplus is now mature enough to be useful as well as being actively developed. It can also do quite a few tricks pyste cannot.""" If this is really the case, I think the Boost documentation needs to say so. For example, the doc page <<http://www.boost.org/libs/python/pyste/>> does not give any warning that Pyste is essentially deprecated (which it apparently is, if the above quote is true). Further, as far as I can tell there are no clues at <<http://www.boost.org/libs/libraries.htm#Inter-language>> indicating that users might want to check out pyplusplus, whereas the official Boost.Python page <<http://www.boost.org/libs/python/doc/index.html>> explicity directs users to Pyste. The end result is that an innocent user who is new to integrating Python and C++ (like, um, say, me) could reasonably come away with the impression that the most state-of-the-art approach to use is Boost.Python+Pyste. As a side question, does anyone use Boost.Python *without* an automatic code generator such as Pyste or Pyplusplus? It does not seem like a practical thing to do--but maybe I'm missing something...? Thank you. Michael D.

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