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undefined ref to basic_regex
by Nathan Fain 24 Oct '06

24 Oct '06

i cannot tell why i am having trouble with basic_regex. I followed the installation instructions and had no error on install. g++ -o example -g -O2 -Wall -W -Wno-unused -fno-strict-aliasing example.cc-lboost_regex /tmp/ccFmlTDD.o(.text+0x3c): In function `main': /usr/local/include/boost/regex/v4/basic_regex.hpp:253: undefined reference to `boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::do_assign(char const*, char const*, unsigned)' collect2: ld returned 1 exit status example.cc: #include <boost/regex.hpp> using namespace boost; int main () { regex expr("foo"); return 0; } i compiled and installed boost as follows: ./tools/build/jam_src/bin.linuxx86/bjam -sHAVE_ICU=1 -sICU_PATH=/usr/local/share/icu/3.6 -sTOOLS=gcc -sPYTHON_ROOT=/usr -sPYTHON_VERSION=2.4 --prefix=/usr/local --exec-prefix=/usr/local --libdir=/usr/local/lib --includedir=/usr/local/include install thanks for any help -- cyphunk://cypherpoet.com

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[bind]
by Sebastian Weber 24 Oct '06

24 Oct '06

Hello there! I'm about to explore the power of boost::bind, but I am still a beginner. Maybe the question is rather stupid, but the following code does not compile and I do not understand why: typedef std::vector<std::size_t> data_t; data_t dataVec; ... populate dataVec ... std::size_t shiftIndex = 3; boost::function<std::size_t& (std::size_t)> shiftedData = boost::bind(&data_t::at, &dataVec, _1 - shiftIndex); The error message is something like /home/sweber/graphpkg/libs/boost/boost/function/function_template.hpp:119: error: invalid initialization of reference of type 'size_t&' from expression of type 'const unsigned int' My system is a debian sarge with a g++-3.3 and boost 1.33.1. What I'm trying to do is to shift the index of the data-vector such that index 3 would address the first element. Thanks for any help. Greetings, Sebastian Weber

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OOPSLA Birds of Feather - Tuesday 5:30 PM - Room E147
by Jeff Garland 23 Oct '06

23 Oct '06

For folks in Portland that want to get together and talk about Boost, please stop by tomorrow evening. This will be an open session to discuss anything you'd like to about Boost, ask questions about the Portland committee meeting, Google SoC, or any other vaguely related Boost topic. See ya there! Jeff

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Implementation of Exponential Distribution
by Nelis Franken 23 Oct '06

23 Oct '06

Hi, I've been looking into statistical distributions, and while comparing Wikipedia's mathematical formulation and Boost's implementation of the Exponential Distribution, I have found two points of interest. Before continuing, I just need to add that I'm not a statistician or a mathematician, so any errors either mathematical or in interpretation below are my own. The Wikipedia reference: http://en.wikipedia.org/wiki/Exponential_distribution The Boost implementation (line 54 of exponential_distribution.hpp) -result_type(1) / _lambda * log(result_type(1)-eng()); Where the eng() call generates a uniform random number. The first, less critical point: If eng() is uniform, then so is (1 - eng()), which allows for the simplification of the statement passed to log() from: log(result_type(1)-eng()) to log(eng()) The second, more critical point: The implementation does not seem to be the correct inverse of the original function. Boost's implementation (with above modification) is: -result_type(1) / _lambda * log(eng()); But should actually be: -log(eng()) / _lamda; Could someone perhaps clarify the above? Again, apologies if my interpretations were wrong. Kind regards, Nelis Franken

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Re: [Boost-users] [bind]
by Sohail Somani 23 Oct '06

23 Oct '06

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of > Stuart Dootson > Boos.Bind will only do the binding bit - what you're wanting to do > (apply an expression to the parameter at call-time) can be > accomplished with Boost.Lambda - which has its own bind facility (with > pretty much exactly the same syntax as Boost.Bind) that you'll need to > use instead of Boost.Bind. Do you know if there are any plans to unify boost bind and lambda bind? I have heard about it...

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[boost::shared_ptr] performance killer
by Ovanes Markarian 23 Oct '06

23 Oct '06

Hello, we have some application, where boost::shared_ptr is extensively used. After profiling with gprof I got that the shared_ptr destructor is very expensive. I used following g++ compiler flags to compile: -Wall -ftemplate-depth-50 -fexceptions -fexpensive-optimizations -O3 Are there may be some MACRO-defs, which can enable/disable some additional optimizations? With Kind Regards, Ovanes Markarian

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[mpl::map] question for Dave ;)
by Ovanes Markarian 23 Oct '06

23 Oct '06

Dave, sorry to address you directly. I assume you were absent last week, so nobody answered my posts. :( Can you take a look at them? I have a problem resizing mpl::map to 150 elements. http://lists.boost.org/boost-users/2006/10/22961.php http://lists.boost.org/boost-users/2006/10/22988.php With Kind Regards, Ovanes Markarian

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[Numeric.Interval_Lib] typecasting behaviour
by tirath 23 Oct '06

23 Oct '06

Hi all, Background... I'm using the interval arithmetic library to evaluate the accuracy of different algorithms for my application (i.e. I'm using the library "offline"; once a winner is chosen, the interval arithmetic will be removed). One possibility that I am pursuing is using mixed precision arithmetic; i.e. do some parts in double precision, some parts in single precision - this is to explore the possibility of eventually utilising non-conventional processing hardware such as GPUs, which tend to have only single precision arithmetic hardware. The query... Before I started using the library, I had this assumption: let A be a float with an exact representation (i.e. width=0). If we cast A to a double, the resulting double will have a non-zero width - specifically the width will be equal to the extra precision afforded to doubles vs floats. Unless I've messed something up, I find that the library does not actually behave this way, and to be frank, I think it ought to! :-) Here's the simple testcase: typedef interval<float> I1; typedef interval<double> I2; I1 y = 1.0; I2 yy = (I1)y; cout << yy.upper() - yy.lower(); I expected yy.upper()-yy.lower() to be non-zero, but it was zero. I had a look at the policies but couldn't spot anything obviously relevant to this situation. Any thoughts on this behaviour per se, or any ideas on a neat and elegant way to implement my desired behaviour? FWIW, my system is PowerPC G4 with powerpc-apple-darwin8-g++-4.0.0 (GCC) 4.0.0 20041026 (Apple Computer, Inc. build 4061). -tirath

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creating lambda expressions incrementally
by Arnaldur Gylfason 23 Oct '06

23 Oct '06

Hi, I´m writing a simple expression parser in boost::spirit that can parse a string like "_1 + _2" or "log(_1)" and return a function object that does just that. I used boost::lamda for that and return it as boost::function object. Now I want to parse compositions like "sqrt(_1*_1 + _2*_2)" or "(_1 + _2)*_2" etc. It is easy to parse this of course but I have to create the corresponding function incrementally (in a loop or recursively) and that means I have to keep incremental lambdas until the whole expression has been created. I can not store them as boost::function since they do not work with lambda operator overloading (apart from the fact that it would be too costly). I need a lambda type for these intermediate lambda objects. I guess the auto type specifier would solve this but when will that be available I wonder? The typeof seems to provide a solution though. I was just trying it and it seems to work! Am I on the right track or am I overlooking something? If anyone knows a better solution please tell me! cheers Arnaldur Gylfason

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[BGL] Correct way to retrieve properties
by Leandro Melo 23 Oct '06

23 Oct '06

Hi, I'd like to make about whether this is the correct way to retrieve a vertex (or edge) property from graph. In this case, the vertex is property is my_v_prop and the edge property is my_e_prop. //... typedef adjacency_list<vecS, vecS, directedS, my_v_prop, my_e_prop> Graph; //.... std::pair<VI, VI> vi = vertices(g); //VI are vertices iterators. for (; !(vi.first == vi.second); ++vi.first) { vertex_descriptor v = *vi.first; //Now, I want to retrieve the property of v. my_v_prop data = g[v]; } Is it the the best/fastest/easiest way to retrieve the property? Thanks. -- Leandro Terra C. Melo

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