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The C++ Post-Processor
by Christian Schladetsch 02 Nov '09

02 Nov '09

Hello, This is a general post about C++. Why is it that the pre-processor (PP) is the source of so much disdain, and yet it is the first resource exploited to 'fix' problems with C++? Why has the PP received so little attention over the years, from its early use as M4? This is a message to the powers that be: the PP is a powerful tool. It provides a 'context-cutting' mechanism for creating and extending solutions. It is a true "meta-programming" system built right into C++. No other language I can think of has a PP. This is often viewed as being a good thing, but I wonder more and more as I get older that a good PP is in fact needed to span some otherwise very difficult boundaries. Other languages are "dynamic" inasmuch as they reflect classes and allow for runtime changes to types and instances. I think we all here agree that this ability is counter to building firm, safe and efficient software. But the PP is similar to that, allowing a degree of dynamicy not otherwise available. Specifically, by exposing concepts to the PP we can leverage reflection and synthesis while building on inheritance and conglomeration. I don't have a point as such; I just wanted to raise the idea of developing M4 and the PP past where it is. There is a lot of low-hanging fruit there. This is evidenced by the fact that a lot of other languages are or can be transliterated to C++. Rather than thinking of C++ as the output, we could be thinking of C++ as the input. Perhaps a way forward for C++ is a good PP and a standards-based implementation of C++ in C++ so it can embed itself. I've written a number of languages, and in each I've had to address the issue of pre-processing. The latest attempts have resulted in a system where it parses and executes via AST input to produce an output that is then parsed by the same system to produce an AST that is then walked to eventually produce machine code. I think this model is best, and would be delighted to see some similar movements in the PP/C++. We have Boost.Wave to start with... Why not give it real Expressions? Loops? Scopes? Classes? Templates? memory management? IO? Is there any interest in a Boost.C++ ? Regards, Christian

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[optional] layout
by Domagoj Saric 01 Nov '09

01 Nov '09

why is boost::optional laid out so that the bool comes before the object's placeholder/storage? this takes up to 7 extra bytes of storage with default alignement and, more importantly, it forces pointer offset adjustment/calculation when accessing a boost::optional<> through a pointer (and trying to access the actual contained object)... it also makes life harder for those of us keen to hackery ;) because it makes the address of an optional different from the address of the actual object within the optional... ps. it would be 'cool' if all of the functionality from boost::optional<> not related to the 'is initialized' bool (conditional destruction, etc...) could be extracted into a separate class (usefull for cases where you have to delay/in-place construct an object but are certain that you will construct it by the point where it needs to be used or destroyed...so you do not need the 'conditional' overhead)... -- "That men do not learn very much from the lessons of history is the most important of all the lessons of history." Aldous Huxley

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Re: [boost] loglite - A logging library (JD)
by Tan, Tom (Shanghai) 01 Nov '09

01 Nov '09

> Please have a look and let me know what you think could be improved. The first thing I notice is that it does not support std::wstring directly. It's a big problem in my case I use wide-character in all my applications, which simplifies dealing with UTF-16 adopted by Modern Windows platforms. If I need to any string info from my program, I'll have to convert from UTF16(represented as std::wstring) to UTF8 so that it could be working well with LOGLITE. That's inconvenient. Offtopic, I am expecting boost::filesystem V3 for this very same reason.

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[ANN] CLI command line interface compiler for C++
by Boris Kolpackov 29 Oct '09

29 Oct '09

Hi, I am pleased to announce the first public release of CLI. CLI is an open-source (MIT license), cross-platform command line interface compiler for C++. It allows you to specify the options that your program supports, their types, and default values. For example: include <string>; class options { bool --help; std::string --name = "example"; unsigned int --level | -l = 5; }; This specification can then be automatically translated to C++ classes that implement parsing of the command line arguments and provide a convenient and type-safe interface for accessing the extracted data. For example: #include <string> class options { public: options (int argc, char** argv); options (int argc, char** argv, int& end); bool help () const; const std::string& name () const; unsigned int level () const; ... }; int main (int argc, char* argv[]) { options o (argc, argv); if (o.help ()) print_usage (); if (o.level () > 4) cerr << "name is " << o.name () << endl; ... } It is easy to start using CLI in your application since there are no external dependencies. You can compile your command line interface to C++ and simply add the generated files to your project's source code. For a five minute introduction to CLI, see the "Hello World" example in the CLI Getting Started Guide: http://www.codesynthesis.com/projects/cli/doc/guide/#2 More information, documentation, and source code distributions are available from the project's web page: http://www.codesynthesis.com/projects/cli/ Enjoy, Boris -- Boris Kolpackov, Code Synthesis Tools http://codesynthesis.com/~boris/blog Open-source XML data binding for C++: http://codesynthesis.com/products/xsd XML data binding for embedded systems: http://codesynthesis.com/products/xsde

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Re: [boost] [Boost-users] at_thread_exit() never getting called
by vicente.botet 29 Oct '09

29 Oct '09

Hi, ----- Original Message ----- From: "cowwoc" <cowwoc(a)bbs.darktech.org> To: <boost-users(a)lists.boost.org> Sent: Wednesday, October 28, 2009 7:33 PM Subject: Re: [Boost-users] at_thread_exit() never getting called > > > I think https://svn.boost.org/trac/boost/ticket/2739 prevents it from > working. > > Gili > > > Steven Watanabe-4 wrote: >> >> AMDG >> >> cowwoc wrote: >>> I am registering boost::this_thread::at_thread_exit() against one of my >>> threads. When the main thread exits using "return 0" the at_thread_exit >>> hook >>> never gets invoked. Is this normal? >> >> It's supposed to work for the main thread... For me yes, but it dosn't works. The example attached to the ticket show the problem. >>> Is there a way to hook the main thread >>> shutting down? >>> >> >> On windows you can use on_thread_exit(). >> The patch worked when I summited it. Anthony, I've see that you have started to integrate the patch for the thread attributes. Do you plan to integrate this patch also? Thanks, Vicente

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what is the interest of In Place factory
by rodrigue pons 29 Oct '09

29 Oct '09

Hello, I was looking about the boost In Place Factory to resolve a problem i got, and there is something i don't understand: what is the advantage of this lib? For example: I get a class A, wich constructor is: A( int, const string& ); And an another class, C, that contains an A*. C provides a method to construct this A*: void C::BuildA( int i, const string & str ); wich will be called this way: instance_of_C.BuildA( 1, "test" ); If now i use the boost In Place Factory, the member function C::BuildA will become: template<class InPlaceFactoryT> void C::BuildA( InPlaceFactoryT const& factory ) wich will be called this way: instance_of_C.BuildA( 1, "test" ); We can see here that with or wothout the In Place Factory, the code is exactly the same. So i guess there is something i didn't understand. But what?

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boost.math
by rodrigue pons 29 Oct '09

29 Oct '09

Hello, i need to implement the computation of huges series. These series are made of floats, and thus the error propagates. The problem is that the main constrain is the execution time, thus i must use the more "native" type possible. Is boost.math offer a solution to minimize this error? Which type of float (float, double, any structure?) must i use? Thanks.

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[spirit][regex] rxstrlit/regex_p with wchar_t strings
by Adam Badura 29 Oct '09

29 Oct '09

Is it possible to use rxstrlit/regex_p with wide character strings (wchar_t based)? Or even better, with arbitrary char type/char traits pair? I tried this with suggested example (http://www.boost.org/doc/libs/1_40_0/libs/spirit/classic/example/fundamenta…) and after converting to wchar_t what was required and compiling it run successfully. But it generated a lot of warnings about converting wchar_t to char in headers that looked like regex headers. So I guess it worked only because the wchar_ts in the example are actually chars. If I changed the example to use wchar_t which have no corresponding char values the example would likely fail. In the end I have a string with templated char type and traits type (just like with string and iostream library). And I want to match it against grammar build from (among others) strings with the same char type and traits type. Can I force regex in Spirit to do that? Adam Badura

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Why BOOST_HAS_DECLSPEC is not defined under MingW?
by Artyom 29 Oct '09

29 Oct '09

Hello, I've noticed following lines under boost/config/platform/win32.hpp #if !defined(__GNUC__) && !defined(BOOST_HAS_DECLSPEC) # define BOOST_HAS_DECLSPEC #endif Why? GCC provides support of declspec, Why it is specifically undefined? It can auto-export symbols but it does not work when static members involved. Thanks, Artyom

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Re: [boost] New boost packaging suggestion for windows
by Julian Bangert 29 Oct '09

29 Oct '09

Hello, > Sadly, the only point being discussed so far is the online registration. > What I find to be at least as annoying is the size of the package. And > by that I'm not (only) referring to the memory or bandwidth. The most > important issue is the burden of having to deal with such an amount of > data, even if I'm only interested into a relatively small part of boost. > My package contains everything in one archive. These 37MB offer quite good compression and you can choose what you wish to extract. > I wonder whether there is still any thought or even effort spent on > breaking boost up into individual components that can be built, tested, > and ultimately also packaged separately. Any news on that ? > > Thanks, > Stefan > Well, a lot of Linux distributions already have this ( all the libboost- packages in debian for examples ) . In W32 it is possible even with BoostPro and in my distribution you can selectively extract libs. Tell me if this is wanted/appreciated and I can write a GUI frontend to automatically install components. I just uploaded the files to 2 sites for distribution, at least one of which should be up at any given time: 1) ( the mirror, but the preferred location ) http://boost-win-bin.googlecode.com/files/boost_1_40_0-vc9-preview.7z* 2) ( main site, but not on a good machine) https://obliviononline.com/pub/boost/ *After a few people confirm that this works for them they should be considered stable and I would build for other C versions as well. Then they could also be mentioned in getting started. * *Thanks, Julian Bangert __________ Information from ESET NOD32 Antivirus, version of virus signature database 4553 (20091028) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com

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