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[iostreams] How do you flush an entire filter chain?
by Adam Nielsen 05 Dec '10

05 Dec '10

Hi all, I have some code that uses standard C++ iostreams and I would like to use Boost iostreams to insert a filter in the process to provide transparent XOR encryption/decryption without needing to modify the existing code. I have written a filter that applies the algorithm, and I create a filtering_stream<io::seekable> "stack" which has the XOR filter pushed onto it, followed by the original iostream. I then pass this stack along to the original function and for the most part it works. However when the original code tries to flush() the changes back to disk, the filter only calls flush() on the first item in the stack. This means the XOR algorithm has its flush() function called, but the iostream (next in line on the stack) does not. If I remove the XOR algorithm (leaving the filter stack in place) then it does call flush() on the original iostream now that it is the first element in the stack. So I would like to know if there is a way to flush an entire filter stack, rather than just the top-most element in the stack. My XOR filter function doesn't actually perform any caching so its flush() function simply returns true, as this seems to be required from what I could make out in the docs about flushing. I was unable to find any mention in the docs of how flush() should behave in a filter (not even a function signature) so I am not sure if this is correct! I just copied it off some of the test code as that was the only place I could find anything about it. Many thanks, Adam.

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[gil] Using gil::color_converted_view with gil::for_each_pixel
by Chris Yuen 04 Dec '10

04 Dec '10

Hey guys, I realized that writing to gil::color_converted_view doesn't affect the underlying view's data. I wonder if that's correct? For example, let's say that I want to write a program that will take the value of the red channel and set the blue channel's value to half of that. Here's my failed attempt: template <typename SrcView> void half_red_to_blue(SrcView & view) { // Since SrcView might be RGB or BGR or some other types, // I decided to use a color_converted_view to ensure that I'm // accessing the correct channels type gil::color_converted_view_type<SrcView, gil::rgb8_pixel_t>::type MyView; MyView my_view = gil::color_converted_view<gil::rgb8_pixel_t>(view): struct my_lambda { void operator()(gil::rgb8_pixel_t & p) { p[2] = p[0] / 2; } }; gil::for_each_pixel(my_view, my_lambda()); } However, it only works when SrcView is not actually gil::rgb8_view_t. If I call, e.g. half_red_to_blue<gil::bgr8_view_t>(view), the view is not changed at all! I inspected a little in the debugger and it seems the write operation is writing to some kind of proxy location instead of the original pixels. Any ideas? Thanks in advance! Best regards, Chris Yuen

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Runtime identity
by Robert Jones 04 Dec '10

04 Dec '10

I'm not sure if this is a stupid question, but is there a runtime equivalent of boost.mpl's identity metafunction? Something that just returns it's single argument, eg., template <typename T> T identity( T t ) { return t; } I think it's trivially simple to write, but I wonder if it already exists in Boost or indeed the STL? (I need this because I need to pass a function object which simply returns an object I already have - maybe I've missed a more obvious method?) Thx, Rob.

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[Process] Can't build example
by benedikt.leschitzki＠gmx.de 04 Dec '10

04 Dec '10

Hi there, I just downloaded the current version of the Process library and tried to build the first example from the tutorial [1], but I get the following error: ############################################################### C:\Programme\boost\boost\process\detail\pipe.hpp||In constructor 'boost::process::detail::pipe::pipe()':| C:\Programme\boost\boost\process\detail\pipe.hpp|129|error: no matching function for call to 'boost::system::system_error::system_error(DWORD, const boost::system::error_category& (&)(), const char [54])'| C:\Programme\boost\boost\system\system_error.hpp|43|note: candidates are: boost::system::system_error::system_error(int, const boost::system::error_category&, const char*)| C:\Programme\boost\boost\system\system_error.hpp|39|note: boost::system::system_error::system_error(int, const boost::system::error_category&, const std::string&)| C:\Programme\boost\boost\system\system_error.hpp|36|note: boost::system::system_error::system_error(int, const boost::system::error_category&)| C:\Programme\boost\boost\system\system_error.hpp|33|note: boost::system::system_error::system_error(boost::system::error_code, const char*)| C:\Programme\boost\boost\system\system_error.hpp|30|note: boost::system::system_error::system_error(boost::system::error_code, const std::string&)| C:\Programme\boost\boost\system\system_error.hpp|27|note: boost::system::system_error::system_error(boost::system::error_code)| C:\Programme\boost\boost\system\system_error.hpp|25|note: boost::system::system_error::system_error(const boost::system::system_error&)| C:\Programme\boost\boost\process\detail\win32_ops.hpp||In function 'boost::shared_array<char> boost::process::detail::collection_to_win32_cmdline(const Arguments&)':| C:\Programme\boost\boost\process\detail\win32_ops.hpp|87|error: '::strcat_s' has not been declared| C:\Programme\boost\boost\process\detail\win32_ops.hpp||In function 'boost::shared_array<char> boost::process::detail::environment_to_win32_strings(const boost::process::environment&)':| C:\Programme\boost\boost\process\detail\win32_ops.hpp|127|error: '::memcpy_s' has not been declared| C:\Programme\boost\boost\process\detail\win32_ops.hpp||In function 'PROCESS_INFORMATION boost::process::detail::win32_start(const Executable&, const Arguments&, const boost::process::environment&, boost::process::detail::stream_info&, boost::process::detail::stream_info&, boost::process::detail::stream_info&, const boost::process::detail::win32_setup&)':| C:\Programme\boost\boost\process\detail\win32_ops.hpp|333|error: '::strcpy_s' has not been declared| C:\Programme\boost\boost\process\detail\win32_ops.hpp|340|error: '::strcpy_s' has not been declared| C:\Programme\boost\boost\process\self.hpp|90|warning: declaration of 'char** boost::process::__p__environ()' has 'extern' and is initialized| C:\Programme\boost\boost\process\self.hpp|90|error: invalid pure specifier (only '= 0' is allowed) before 'GetEnvironmentStrings'| C:\Programme\boost\boost\process\self.hpp|90|error: function 'char** boost::process::__p__environ()' is initialized like a variable| C:\Programme\boost\boost\system\error_code.hpp|214|warning: 'boost::system::posix_category' defined but not used| C:\Programme\boost\boost\system\error_code.hpp|215|warning: 'boost::system::errno_ecat' defined but not used| C:\Programme\boost\boost\system\error_code.hpp|216|warning: 'boost::system::native_ecat' defined but not used| ||=== Build finished: 7 errors, 4 warnings ===| ############################################################### What should I do? I'm using g++ version 4.4.1 from the mingw Package under Windows XP 32 bit. [1] http://www.highscore.de/boost/process/process/tutorials.html#process.tutori…

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Problem building boost 1.45.0
by benedikt.leschitzki＠gmx.de 04 Dec '10

04 Dec '10

Hi, I just downloaded the latest boost version and wanted to build the library for MS-Windows XP 32 bit using the mingw compiler set. According to [1], building should be done using bootstrap.bat to build the bootstrap.bat. If I start it, it just gives me this message, no matter what first argument I give (I tried gcc, gcc-nocygwin, mingw): ######################################################################## Building Boost.Jam build engine Failed to build Boost.Jam build engine. Please consult bjam.log for furter diagnostics. You can try to obtain a prebuilt binary from http://sf.net/project/showfiles.php?group_id=7586&package_id=72941 Also, you can file an issue at http://svn.boost.org Please attach bjam.log in that case. ######################################################################## bjam.log: ######################################################################## ### ### "Could not find a suitable toolset." ### ### You can specify the toolset as the argument, i.e.: ### .\build.bat msvc ### ### Toolsets supported by this script are: borland, como, gcc, gcc-nocygwin, ### intel-win32, metrowerks, mingw, msvc, vc7, vc8, vc9, vc10 ### ######################################################################## Trying to build boost with the precompiled bjam (03.1.18) yields the following error: ######################################################################## C:/Programme/boost_1_45_0/tools/build/v2/build\configure.jam:145: in builds-raw *** argument error * rule UPDATE_NOW ( targets * : log ? : ignore-minus-n ? ) * called with: ( <pbin.v2\libs\regex\build\gcc-mingw-4.4.1\debug>has_icu.exe : : ignore-minus-n : ignore-minus-q ) * extra argument ignore-minus-q (builtin):see definition of rule 'UPDATE_NOW' being called [Entire error is here: http://boost.codepad.org/PbZYNTm5] ######################################################################## What should I do to build boost successfully? My g++ version is 4.4.1. [1] http://permalink.gmane.org/gmane.comp.lib.boost.build/23347

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[Spirit 2] Questions related to generating grammars meta-dynamically
by Max Motovilov 03 Dec '10

03 Dec '10

I'm trying to create a serialization facility that builds the underlying Spirit grammars based on a data model extracted from user-supplied types (I guess meta-dynamically ought to be the right word :) ). In doing so, I seem to quickly run out of documentation coverage and accumulate questions that are not easily answered by perusing the source code. Here are the more painful members of that collection, posted in the hopes that someone more informed might answer them for me: - What are the respective scopes of the rule and the grammar? Specifically, within a parser expression (situated within a grammar's constructor, according to the pattern established in the examples) which of the locals<> can I refer to in the sub-expressions specifying explicit parser parameters and semantic actions? - I'd like to write a functor that selects one of the grammars from a list (Fusion sequence), and passes an argument (inherited attribute) to it; the [parser-like] result returned by this functor would then be used in an enclosing parser expression. Is there an easily computable type that such a functor can return? I have noticed that the implementations of grammar<>::operator() return a very intricate construct that would be hard to replicate outside Spirit code -- proto::terminal< spirit::qi::parameterized_nonterminal< start_type, supplied-argument-types... > > -- but maybe there is a simpler front-end type the above is convertible to and that will still work as a component of parser expression? Thanks in advance, ...Max...

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[netlib] Update: 0.9 will not be header-only
by Dean Michael Berris 03 Dec '10

03 Dec '10

Hi Everyone, To those who are following the development of cpp-netlib (which shall be submitted for review /soon/ as Boost.Netlib), the current state of 0.9-devel and thus what's going to come out officially as 0.9 in a couple of weeks, will not be header-only. Aside from the obvious reason that the compile-times are starting to become unbearable (>10 minutes to build the whole test suite!!) and after noticing that the intended simplicity of the API with tag-metafunction dispatch is limiting the expressiveness of the HTTP client types, the 0.9 release will be the first release that will require an externally linked-in static library. The biggest culprit at the moment has been the implementation of the URI parser that uses Boost.Spirit Qi and >10 rules in the URI parsing grammar. The URI implementation is really declarative and nicely written (thanks go out to Jeroen Habraken for making that happen). The down-side of this has been the compile times: building the simple HTTP client takes close to one minute on the machine I'm using -- and by moving it to an externally-linked static lib, the compile of the same HTTP client is cut down to 10 seconds. Before you ask if I'm using GCC, the answer is no, I'm using Clang when developing so that I get as much speed as I can when doing the edit-rebuild-test cycle. I've written about what I've been doing and what I'll be doing in my three recent articles at C++ Soup. If you want to get more details, please follow the links below. http://cplusplus-soup.com/2010/12/03/cpp-netlib-moving-away-from-header-onl… http://cplusplus-soup.com/2010/12/02/cpp-netlib-demolition-day/ http://cplusplus-soup.com/2010/12/01/cpp-netlib-reducing-compilation-times/ Have a great weekend everyone, please send your qestions/comments/suggestions over either directly to me or through the various mailing lists (Boost-devel, Boost-users, cpp-netlib-devel). -- Dean Michael Berris deanberris.com

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NewBie: help needed generating documentation with quickbook and bjam
by Wilhelm 03 Dec '10

03 Dec '10

Hello, this is a absolute newbie question: I try to write some documentation using quickbook. I was able to generate a .xml file. But now I have no idea how to produce a html or pdf version thereof. I read some documentation about bjam and installed the neccessary libraries (I hope). But I didn't find any documentation about how to write a .jam file for this purpose. Can someone help solving this (dumb) question? -- Wilhelm

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boost/parameter/keyword.hpp warning, TI compiler
by Krzysztof Czainski 03 Dec '10

03 Dec '10

Hello, When I compile a file, that consists of only one line: #include <boost/parameter/keyword.hpp> with a Texas Intstruments compiler for DSP (cgtools-6.1.12); boost-1.45.0, I get this warning: boost/parameter/aux_/void.hpp, line 20: warning #1369-D: static local variables of extern inline function are not resolved to single copy. Not ANSI C++ Compliant It referes to: inline void_& void_reference() { static void_ instance; return instance; } In this particular context this warning seams harmless, so I would like to suppress it. As far as I know, this compiler doesn't have a #pragma warning(disable:1369) equivalent... I know how suppress this kind of warning globally, but I would not like that, because in other contexts this is an important warning. Any ideas, how I could suppress this warning locally, in code perhaps? Cheers Kris

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[Units] unary minus on units is counter intuitive (or a bug)
by alfC 03 Dec '10

03 Dec '10

Hi, I found this counterintuitive result of applying the unary minus operator to a unit "- si::meter" is the same as "si::meter" (or any other unit). or worst std::cout << - si::meter*1. << std::endl; // prints 1*m i.e. the minus is explicitly ignored. The root of the problem is this curious line in boost/units/unit.hpp /// unit runtime unary minus template<class Dim,class System> typename unary_minus_typeof_helper< unit<Dim,System> >::type operator-(const unit<Dim,System>&) { typedef typename unary_minus_typeof_helper< unit<Dim,System> >::type type; return type(); } a more intuitive result (but not completely elegant) could be attained by defining instead: template<class Dimension, class System> quantity<unit<Dim, System> > operator-(unit<Dim, System> const& u){ return -1.*u; } This is a definition that I could add BUT it will conflict with the original definition. Another way, could be to specialize unary_minus_typeof_helper<...>::type to be something that is not a unit but holds the negative "direction" and the cast to Type(-1)*unit quantity but it seems overly complicated for the purpose. Note aside: Why would I need "minus units" in the first place? The original code that produced the confusion was - kB*T which appears commonly in physics. kB is the "atomic" unit of entropy/ specific heat (atomic::heat_capacity) and T is a temperature quantity. This was parsed as (-kB)*T and then as kB*T i.e. the minus sign was ignored all together. In my opinion unary operator- should not be defined for units in the first place. The current definition only makes things worst, by creating a counter intuitive result AND making the fix conflict with the definition. Thoughts? Thank you, Alfredo

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