December 2010 - Boost-users - lists.preview.boost.org

Re: [Boost-users] [gil] Using gil::color_converted_view with gil::for_each_pixel
by Chris Yuen 05 Dec '10

05 Dec '10

Hello Christian, Thanks for your guidance! I took a look at semantic_at_c() and get_color() and they seem to do the trick! Here's a couple of more questions. I've posted a compiling, annotated code at http://boost.codepad.org/Fy2vP73l Below is the more elaborate description of my questions which can be found in the code: 1. Can I specify which channel to get in nth_channel_view()? For example, if I want to set the red channel to 255 for all the pixels, I would do gil::fil_pixels(gil::nth_channel_view(view, 0), 255). However, that only works if our view is rgb8 or bgr8, not argb8. Is there a way I can say something like gil::fill_pixels(gil::nth_channel_view(view, gil::find_channel_for_view(view, gil::red_t())), 255) ??? 2. This compiles gil::gil_function_requires<gil::ImageViewConcept<int> >(); Strange. Any ideas? Best regards, Chris Yuen P.S. I am definitely interested in reviewing the extension! Apparently I'm a begginer in GIL. How would you like me to review and where should I write to?

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Help with Visual Studio settings for Boost Serialization
by Abdullah ARSLAN 05 Dec '10

05 Dec '10

I am trying to implement very simple sample of boost serialization. I have a sample class, class1. It only contains a simple int variable. I followed the examples given here : http://www.boost.org/doc/libs/1_45_0/libs/serialization/doc/index.html <http://www.boost.org/doc/libs/1_45_0/libs/serialization/doc/index.html> I also think that i followed this guideline : http://beta.boost.org/doc/libs/1_44_0/more/getting_started/windows.html but i am not sure... Here is the error i get: error LNK2019: unresolved external symbol "private: void __thiscall class1::serialize<class boost::archive::text..... Could you help me with this error or could you guide me with installation and running a very simple serialization example, step by step... like download this, install this and etc... I am using visual studio 2008 express... Thanks in advance..

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[message_queue.hpp]is it possible to retrieve a file descriptor for a boost message queue
by rohini chandra pallapothu 05 Dec '10

05 Dec '10

Hi, Could you anyone please let me know if it is possible to wait on a boost message queue (even if it is in the future versions of boost). I could not find any function from the boost documentation that can be used to retrieve a file descriptor of boost message queue.I wanted to get it confirmed. Best Regards, Rohini Chandra

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Lexical_cast and hex number
by Claude 05 Dec '10

05 Dec '10

Hi! It is possibile to transform a string representing a hexadecimal number in the format "0xnumber" or "number" (without "0x") in an integer with lexical_cast<>? -- View this message in context: http://boost.2283326.n4.nabble.com/Lexical-cast-and-hex-number-tp3070247p30… Sent from the Boost - Users mailing list archive at Nabble.com.

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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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