- Boost-users - lists.boost.org

[boost-users] converting InputIterator to ForwardIterator
by Igor R 11 Mar '09

11 Mar '09

Hello, I'd like to do the subj, in order to be able to apply some std algorithms to files, like this: ifstream file("myfile", std::ios::binary|std::ios::in); std::string delim("\r\n\r\n"); // sequence to search typedef std::istreambuf_iterator<char> iterator; iterator begin(file), end; iterator pos = std::find_end(begin, end, delim.begin(), delim.end()); // won't work, because istreambuf_iterator is *not* ForwardIterator I found something called multi_pass in boost::spirit. However, I'm not sure if it's relevant or deprecated class (it seems to be a part of the "old" Spirit), and whether this's the only Boost utility I can use to perform the above conversion. Thanks.

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[interprocess] Memory mapped file based allocator
by dhruva 11 Mar '09

11 Mar '09

Hi, I am looking for a memory mapped file based allocator that does not map the whole file into memory. The size may be huge and I would not want to map all the contents into process memory. Since my read and write access are sequential, I would like the mapping to happen on demand (based on access violation trying to read an unmapped region of memory). Is there something like that in Interprocess/Boost (since the implementation needs to work both on M$ and GNU/Linux)? regards, dhruva Bollywood news, movie reviews, film trailers and more! Go to http://in.movies.yahoo.com/

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[Random] Sigma equal to zero in normal distribution.
by Rodolfo Federico Gamarra 11 Mar '09

11 Mar '09

Hi all, The documentation for the normal distribution (http://www.boost.org/doc/libs/1_38_0/libs/random/random-distributions.html#…) states: "Members explicit normal_distribution(const result_type& mean = 0, const result_type& sigma = 1); Requires: sigma > 0" In the actual code of this constructor (http://www.boost.org/doc/libs/1_38_0/boost/random/normal_distribution.hpp) it can be seen "assert(_sigma >= result_type(0));". That is, acepts sigma == 0. Indeed, there's no "division-by-zero" or so, because the method that is used ("Box-Muller") doesn't actually divide by sigma: return _cached_rho * (_valid ? cos(result_type(2)*pi*_r1) : sin(result_type(2)*pi*_r1)) * _sigma + _mean; So, in this case, the numbers will be all equal to _mean. From the mathematical point of view there's no such thing as a normal distribution with sigma equal to zero; but, computationally, may be handy to allow that. What's the expected behavior? Is there a typo in the docs? Or is it that the case sigma equal to zero is indeed undefined (so that anything could happen)? Thanks in advance, cheers. -- Rodolfo Federico Gamarra

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Thread usage in boost other then boost.thread??
by Bill Taylor 11 Mar '09

11 Mar '09

Hello, I joined the list because I am helping a PHD candidate run a very long program with Condor. But the mode we need to use does not work if pthreads are used because we can not save the state of the job when it needs to run somewhere else. Is it known what components in the boost library use threads? Bill Taylor Condor Project

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[asio] when to use io_service::post or deadline_timer::async_wait?
by Markus Werle 11 Mar '09

11 Mar '09

Hi! After reading the referece docs I got the impression that the only difference between io_service::post and deadline_timer::async_wait is the fact that the former triggers execution immediately (after the caller function returns?) while the latter waits until timer expires before execution of the function object. Is this really the only difference or is there any other issue to be considered? Markus

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Generalised compile-time hash function
by Nikhilesh S 11 Mar '09

11 Mar '09

Hey guys! I'm not very familiar with boost.mpl, or boost.preprocessor, so I wanted to ask. I've written a compile-time hash function. Here's an example that uses it:- #include <iostream> using namespace std; //Compile-time hasher. #define HASH(partial,c) (((partial) << 1) ^ (c)) #define HASH_1(p1) HASH(0,(p1)) #define HASH_2(p1,p2) HASH(HASH_1(p1),(p2)) #define HASH_3(p1,p2,p3) HASH(HASH_2(p1,p2),(p3)) #define HASH_4(p1,p2,p3,p4) HASH(HASH_3(p1,p2,p3),(p4)) #define HASH_5(p1,p2,p3,p4,p5) HASH(HASH_4(p1,p2,p3,p4),(p5)) #define HASH_6(p1,p2,p3,p4,p5,p6) HASH(HASH_5(p1,p2,p3,p4,p5),(p6)) #define HASH_7(p1,p2,p3,p4,p5,p6,p7) HASH(HASH_6(p1,p2,p3,p4,p5,p6),(p7)) #define HASH_8(p1,p2,p3,p4,p5,p6,p7,p8) HASH(HASH_7(p1,p2,p3,p4,p5,p6,p7),(p8)) #define HASH_9(p1,p2,p3,p4,p5,p6,p7,p8,p9) HASH(HASH_8(p1,p2,p3,p4,p5,p6,p7,p8),(p9)) #define HASH_10(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10) HASH(HASH_9(p1,p2,p3,p4,p5,p6,p7,p8,p9),(p10)) #define HASH_11(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11) HASH(HASH_10(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10),(p11)) #define HASH_12(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12) HASH(HASH_11(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11),(p12)) #define HASH_13(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12,p13) HASH(HASH_12(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12),(p13)) #define HASH_14(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12,p13,p14) HASH(HASH_13(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12,p13),(p14)) #define HASH_15(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12,p13,p14,p15) HASH(HASH_14(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12,p13,p14),(p15)) #define HASH_16(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12,p13,p14,p15,p16) HASH(HASH_15(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12,p13,p14,p15),(p16)) /* .. omitted the rest, but it's there till around HASH_30 .. */ //Runtime hasher. unsigned int hash(char const *p) { unsigned partial = 0; while (*p) { partial <<= 1; partial ^= *p; ++p; } return partial; } //Test it in a main() int main() { char str[31] = "thisisatest"; //Yay! Switch on strings! switch (hash(str)) { case HASH_11('t','h','i','s','i','s','a','t','e','s','t'): cout << "You said, 'this is a test'!"; break; case HASH_16('y','e','t','a','n','o','t','h','e','r','s','t','r','i','n','g'): cout << "You said, 'yet another string'!"; break; } return 0; } So, I was wondering how I could use boost.preprocessor to be able to write a more generic hash function, something like HASH_GENERIC(mystring), or at least HASH_GENERIC(8,mystring). BTW, here's a vim script that changes any thing like '@something@' on the curent line into "HASH_9('s','o','m','e','t','h','i','n','g')", when you type ',h':- map ,h :s/@$.\+$@/\='HASH_'.strlen(submatch(1))."('".join(split(submatch(1), '\zs'), "','")."')"/<CR> ;-) -- Nikhilesh S http://nikki.drupalsite.org

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Making friend with boost::interprocess
by Oncaphillis 11 Mar '09

11 Mar '09

Hi, I'd like to implement a cross-process singleton which resides in a shared memory segment. So the basic idea is to provide a factory method that is the only way to construct the Singleton. e.g. class Foo { public: static Foo & GetInstance() { try { boost::interprocess::managed_shared_memory segment( boost::interprocess::open_or_create, "FooSegment", 65536); void_allocator_t alloc(segment.get_segment_manager()); return *(segment.find_or_construct<Foo>( "FooObject")(alloc)); } catch(std::exception & ex) { throw; } } private: Foo(const void_allocator_t & a) { ... ... } Foo(const Foo &); } Of course somewhere deep in the guts of boost I get an error since the Foo constructor is private. Who do I have to befriend in order to make this scheme work ? Thank you O.

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pure virtual function call error
by e120281 11 Mar '09

11 Mar '09

class A { public: int i; A( int i ) { this->i = i; } ~A() {} template<class Archive> void serialize(Archive &ar, const unsigned int version) { ar & i; } }; class B { public: B() {} ~B() { std::string filename = "C:\\a2.txt"; const A a( 2 ); std::ofstream ofs( filename.c_str(), std::ios::out | std::ios::binary ); boost::archive::binary_oarchive boa( ofs ); boa << a; } static B* getInstance() { static B instance; return &instance; } void serialize() { std::string filename = "C:\\a1.txt"; const A a( 1 ); std::ofstream ofs( filename.c_str(), std::ios::out | std::ios::binary ); boost::archive::binary_oarchive boa( ofs ); boa << a; } }; int main() { B* b = B::getInstance(); b->serialize(); } When I run the above code in visual studio 2005 I get pure virtual function call error. If I comment out the line b->serialize(); then everything is ok. What is wrong with the above code??? -- View this message in context: http://www.nabble.com/pure-virtual-function-call-error-tp22434024p22434024.… Sent from the Boost - Users mailing list archive at Nabble.com.

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How to build specified library for install?
by Dancefire 11 Mar '09

11 Mar '09

Hi, I am going to build boost::iostreams and install to some location. I tried following command: C:\boost_1_38_0>bjam toolset=msvc variant=debug,release link=static threading=multi runtime-link=shared -sZLIB_SOURCE=E:\zlib123 -sBZIP2_SOURCE=E:\bzip2-1.0.5 --prefix="E:\Program Files\boost\boost_1_38_0\" --with-iostreams install However, I got following error: error: wrong library name 'iostreams install' in the --with-<library> option. It looks like that bjam consider install as a part of the library name. Is anything wrong with me? or it is a bug of bjam? Tao Wang

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[Q] boost class to handle SQL Decimal (19,6)
by V S P 11 Mar '09

11 Mar '09

Hello, I have been searching and searching but could not find a Boost (or Boost-friendly) extension that handles SQL Decimal datatype (in my case decimal (19,6) I did find in Boost's vault http://www.boostpro.com/vault/index.php mp_math_v04 by Baraclese but not clear if it supports decimal point (I did not see any documentation) thanks in advance for any help, Vlad -- V S P toreason(a)fastmail.fm -- http://www.fastmail.fm - Or how I learned to stop worrying and love email again

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