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[boost-users]how to use iostreams::mapped_file
by Sunil Kumar N 18 May '06

18 May '06

Could someone point me to a link for a sample program of using iostreams::mapped_file(except the default tutorial)...I gave a shot at it and snippet is as follows... io::mapped_file_params aparams("c:\\mf.txt"); aparams.new_file_size = 1e8; aparams.mode = BOOST_IOS::out; io::stream_buffer<io::mapped_file> mfStrmBuf(aparams); ostream out(&mfStrmBuf); out << .... keep on writing to file... it works but I need to know how one create a mapped_file that has to grow beyond new_file_size!! That means I dont know the size of the file to be created at compile time!! How to flush explicitly? I am in the process of understanding as to which one offers better performance with respect to time taken when some thousands of lines have to be written to a file.....ofstream vs mapped_file? Thanks in advance :)

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How to write a block-wise filter...
by Stephen Webb 17 May '06

17 May '06

I don't really have my head around the Boost IO filter architecture yet, but I have managed to get a very basic filter working. I'm having some trouble with end-of-input issues. I think what I'm trying to do comes up frequently, so hopefully this will be a straightforward answer... What I'm trying to do is write a filter that takes in input one character at a time (for simplicity -- for now), and outputs encrypted characters. The block size is 4 bytes, so every 4 characters I can encrypt, and then spit out the result. If I hit the end of input, then I want to pad the plaintext, encrypt and output the final block. My trouble is knowing when the end-of-input has arrived. Is there a well defined way that my output filter is notified of a close event or something similar? I did see close functions defined in the example filters, but mine isn't getting called. I tried to look at the base64 encode/decode headers (which would have to deal with the same issue) but I couldn't really follow it. Any help is appreciated. Thanks -Steve

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Re: [Boost-users] [date_time] Need help with a couple simple problems
by Scott 17 May '06

17 May '06

> #include "boost/date_time/local_time_adjustor.hpp" > #include "boost/date_time/c_local_time_adjustor.hpp" > > ptime local_var > =date_time::c_local_adjustor<ptime>::utc_to_local(utc_var); > > What do you mean by the file is in binary format? Thanks for the help. What I mean is I would like to read/write the value of the ptime in the most efficient way possible. So if the ptime is stored as 2 ints, I would like to (de)serialize 8 bytes (4 bytes each int). Portability isn't an issue. What I would rather *not* do is use something like to_iso_string(ptime) and from_iso_string(ptime). The string representation is rather long. But if that's the only way to do it, guess I'll have to make do. Thanks, Scott

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[multi_array] Useful algorithms (from Re: Multi_array: A "proper" iterator over a N>1 Multi_array?)
by Beth Jacobson 17 May '06

17 May '06

On a recent thread, Bruno Martinez provided a std::for_each-like function for multi_arrays which lets users apply a function to each element in a multi_array or view without having to know anything about the dimensions. I've been playing around with it (on MSVC 7.1) and it works perfectly. It seems like a good utility for anyone using boost.multi_array. Working from Bruno's code, I wrote a similar std::accumulate-like function, which could also be generally useful. I'm fairly new to template programming, so if someone could look over the code below and see if I've done something dangerous or stupid, it would be much appreciated. Also, is there some standard Boost way of making this sort of code generally available? It probably isn't at a level where it could be included in the library, but it seems like a shame to just let it languish in the bowels of the mailing list archive. Anyway, here are both algorithms: My accumulate-like function: template<class MA, class T, class F, int dim> struct accum_impl { F f; T &val; accum_impl(T &val, F f) : f(f), val(val) {} T operator()(MA& ma) { std::for_each(ma.begin(), ma.end(), accum_impl<typename boost::add_const<MA::const_reference>::type, T, F, dim-1>(val, f)); return val; } }; template<class Ref, class T, class F> struct accum_impl<Ref, T, F, 0> { F f; T &val; accum_impl(T &val, F &f) : f(f), val(val) {} T operator()(Ref r) { val = f(val, r); return val; } }; template<class MA, class T, class F> T multi_accum(MA& ma, T init, F f) { accum_impl<MA, T, F, MA::dimensionality> impl(init, f); return impl(ma); } And a test: typedef boost::multi_array<int, 3> array_type; typedef array_type::index_range range; typedef array_type::index index; array_type B(boost::extents[4][2][3]); int values = 0; for(index i = 0; i != 4; ++i) for(index j = 0; j != 2; ++j) for(index k = 0; k != 3; ++k) B[i][j][k] = values++; array_type::array_view<2>::type myview = B[ boost::indices[range(1,3)][1][range(0,2)] ]; cout << "Sum: " << multi_accum(myview, 0, std::plus<int>()) << endl; cout << "Product: " << multi_accum(myview, 1, std::multiplies<int>()) << endl; Bruno Martinez's for_each-like function: template<class MA, class F, int dim> struct for_each_impl { F f; for_each_impl(F f) : f(f) {} void operator()(MA& ma) { std::for_each(ma.begin(), ma.end(), for_each_impl<typename MA::reference, F, dim-1>(f)); } }; template<class Ref, class F> struct for_each_impl<Ref, F, 0> { F f; for_each_impl(F f) : f(f) {} void operator()(Ref r) { f(r); } }; template<class MA, class F> void multi_for_each(MA& ma, F f) { for_each_impl<MA, F, MA::dimensionality> impl(f); impl(ma); } And a test: typedef boost::multi_array<double, 3> array_type; typedef array_type::index index; array_type myarray(boost::extents[3][4][2]); typedef array_type::index_range range; array_type::array_view<3>::type myview = myarray[ boost::indices[range(0,2)][range(1,3)][range(0,4,2)] ]; multi_for_each(myview, _1 = 56);

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How to link (properly)
by Jason House 17 May '06

17 May '06

When I run bjam install on my laptop running Mandriva 2006, it places a lot of files in /usr/local/lib with names like libboost_XXX-gcc.a While I know that I can pass -lboost_XXX-gcc and it links, the -gcc bit seems to make things a bit too platform dependent for my liking. What's the proper way to handle that extra bit at the end of the library name? The project I'm working on uses autoconf/configure/make as its build environment.

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Regex Localization problem
by Antonio Scotti 17 May '06

17 May '06

Hi, I have a portability problem with regex (probably due to localization issues). I've found that, under Win32, the regular expression "\w" matches all the alphanumeric chars, including non ascii ones (such as e grave or e acute). This doesn't hold while under linux. In fact, \w only seems to match ascii characters. I've tried chancing the locale, but nothing changed. Is there a way to make \w have on linux the same behaviour it has on win32? Thanks in advance.

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newbie boost::random how can I get a variate_generator for uniform_01 distribution?
by wave style 17 May '06

17 May '06

Hi, I have some strange behavior on win XP with VC 8.0 version and boost::random library. When I use variate_generator helper template with uniform_01 distribution, I always get an compiler error. like as: //code boost::mt19937 rng(time(0)); boost::uniform_01<mt19937> u01(rng); boost::variate_generator<mt19937, uniform_01<mt19937> > die401(rng, u01); //compile info error C2039: 'input_type' : is not a member of 'boost::uniform_01<UniformRandomNumberGenerator>' with [ UniformRandomNumberGenerator=boost::mt19937 ] f:\my documents\visual studio 2005\projects\testboost\testrandom\testrandom.cpp(169) : see reference to class template instantiation 'boost::variate_generator<Engine,Distribution>' being compiled with [ Engine=boost::mt19937, Distribution=boost::uniform_01<boost::mt19937> ] Actually, the uniform_01 class doesn't declare a type named input_type in uniform_01.hpp, because uniform_01 distribution can accept both IntegerType and RealType UniformRandomGenerator. It seems that variate_generator can not support the uniform_01. However, I found the engine_helper struct be specialized for uniform_01 and uniform_int_float in variate_generator.hpp. I got confused. It's vc8.0compiler's bug? How can I get a variate_generator for uniform_01 distribution? Any feedback welcomed!! Thanks. Waveform.

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[boost-build] telling one project to depend on another
by Brian Budge 17 May '06

17 May '06

Hi all - I'm trying out boost-build for the first time, and running into some issues related to project dependencies. I've spent many hours looking at boost-build documentation, and now I'm stuck. My directory structure is laid out like this: -------------------------------------------- base_dir Jamroot simp_envelopes Jamfile ***source*** simp_envelopes ***include files*** my_lib Jamfile ***source*** include ***include files*** test Jamfile tester.cc --------------------------------------------- Basically, my_lib depends on simp_envelopes and test depends on my_lib. In simp_envelopes/Jamfile I have this: ------------ project simplify-libs : usage-requirements <include>simp_envelopes ; lib simplify : [ glob *.cc ] : <include>simp_envelopes ; ------------ which I believe should tell my_libs to include simp_envelopes/simp_envelopes, if only my_libs can know that it should depend on the simp_envelopes project. My Jamroot looks like: ------------ use-project simplify-libs : simp_envelopes ; use-project my-libs : my_libs ; project my_app : requirements <include>.. <include>../SGUL/include : default-build debug ; lib open-mesh : : <file>../OpenMesh/Core/Linux_gcc_max/libOpenMesh_Core.so ; build-project simp_envelopes ; build-project my_libs ; build-project test ; ------------ My my_libs Jamfile: ------------ project my_libs : requirements <include>../simp_envelopes : usage-requirements <include>include ; lib my_libs : [ glob *.cc ] /simplify-libs//simplify : <include>include ; ------------- I had to add the requirements <include>../simp_envelopes for my_libs to find the include files for simp_envelopes... is there a way to get my_libs to depend on simp_envelopes (or simplify-libs) and take care of this automatically? I have similar issues for the test app... I need to at a requirements for the my_libs include directory. Finally, I have defined a library name open-mesh to point to my external library, but I don't know how to have my my_libs essentially require linking against open-mesh. This is in fact even more important because I don't currently have a way of making my application build rule depend on open-mesh. Any help is appreciated! Brian

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[Thread] Get current thread id
by marie-line.gentil2 17 May '06

17 May '06

Is there a boost method which does it? I went through the whole thread documention but could not figure out how to do so.

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assert.h
by dvir schirman 16 May '06

16 May '06

Hi I try to use the random library in order to create a noise signal with normal distribution. I'm using Cygwin platform, and I'm using g++ compiler. I wrote: #include <boost/random.hpp> at the beginning of my header file. and when I tried to compile I got the following error message: In file included from /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/cassert:48, from ../boost/boost/random/linear_congruential.hpp:20, from ../boost/boost/random.hpp:36, from actor.H:12, from tdagent.H:11, from main.C:1: /usr/include/assert.h:6: error: expected unqualified-id before string constant /usr/include/assert.h:6: error: expected `,' or `;' before string constant main.C, tdagent.H, actor.H are files that I've written. I am not familiar with assert.h, I guess it's part of the c++ headers, and that there shouldn't be an error in it. Hope someone can help me solve it. Dvir.

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