July 2008 - Boost-users - lists.boost.org

[function,bind] Templated function<> function
by Michiel Helvensteijn 16 Jul '08

16 Jul '08

Ok, the subject-line might be a bit confusing. :-) I have the following template function: template<class T> bool is(const string& str); Its implementation is not important. It checks if a string can be converted to type T by std::stringstream. I also have the following function: template <class T> function<bool (T)> neg(function<bool (T)> func) { return !bind(func, _1); } Which I use in the following way: BOOST_CHECK_PREDICATE( neg(is<int>), ("text") ); But the compiler (GCC 4.1.2) complains: error: no matching function for call to 'neg(<unresolved overloaded function type>)' What's the problem. And, also, what's the solution? :-) Thanks in advance! -- Michiel Helvensteijn

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[serialization] Visual Studio 2008 + Boost 1.35 : runtime casting not working
by Steve Sanders 16 Jul '08

16 Jul '08

Hi, Below is a basic sample adapted from the documentation at: http://tinyurl.com/55fr4q For me, with Visual Studio 2008, the deserialization of the base pointer results in an instance of the base class, not the serialized derived class. Also, if I add a virtual function to the base class, deserialization results in an exception (it attempts to instantiate the base class anyway). I added the change cited here and rebuilt the serialization library, which did not help: http://tinyurl.com/5j4e8x Any suggestions would be appreciated. Thanks, Steve Sanders #include "stdafx.h" #include "stdafx.h" #include <sstream> // include headers that implement a archive in simple text format #include <boost/archive/text_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> #include <boost/serialization/export.hpp> class base { public: base(){ m_val = 1; } void PrintVal( void ) { printf(" Value: %d\n", m_val ); } protected: // virtual void foo(void) = 0; friend class boost::serialization::access; //... // only required when using method 1 below // no real serialization required - specify a vestigial one template<class Archive> void serialize(Archive & ar, const unsigned int file_version){} int m_val; }; class derived : public base { public: derived(){ m_val = 2; } private: void foo(void){} friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int file_version){ // method 1 : invoke base class serialization boost::serialization::base_object<base>(*this); // method 2 : explicitly register base/derived relationship boost::serialization::void_cast_register<derived, base>( static_cast<derived *>(NULL), static_cast<base *>(NULL) ); } }; BOOST_CLASS_EXPORT_GUID(derived, "derived") void test4(){ //... std::stringstream ss; boost::archive::text_oarchive oa(ss); derived *d = new derived(); base *b = d; b->PrintVal(); oa & d; boost::archive::text_iarchive ar(ss); b = NULL; ar & b; b->PrintVal(); } int main() { test4(); return 0; }

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Can I use boost smart pointer to a pointer a vector of smart pointer to my class
by Meryl Silverburgh 16 Jul '08

16 Jul '08

Hi, In my code, I have this: A pointer to a vector of pointer to A: vector<A*>* Can I switch it to: shared_ptr< vector< shared_ptr <A> > > ? a shared pointer to a vector of shared pointer of A? And when the reference count reaches to 0, will it remove everything? the memory of the vector and all the A objects pointed by the vector?

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Switch from a regular C++ pointer to boost shared_ptr
by Meryl Silverburgh 16 Jul '08

16 Jul '08

Hi, I have a class like this: class A { private: B* b; public: A(); B& getB(); } A::A() { b = NULL; } B& A::getB() { if (b == NULL) { b = new B(); } return *b; } when I switch to use boost shared_ptr, i.e. switch from 'B* b' to 'shared_ptr<B> b' in A's class definition. I don't need to do 'b= NULL' in A's constructor, right? But why this line won't compile "b = new B();" ? I get this error: A.cpp:297: error: no match for 'operator=' in '((const A*)this)->A::xBlockMap = (((B*)operator new(128u)), (<anonymous>->B::B(((const A&)((const A*)this)), ((int)strict)), <anonymous>))' /usr/local/include/boost-1_35/boost/shared_ptr.hpp:194: note: candidates are: boost::shared_ptr<T>& boost::shared_ptr<T>::operator=(const boost::shared_ptr<T>&) [with T = B] Thank you for any help.

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Visual Studio 2008: Link Errors in Debug Mode (__imp____wassert not found).
by Vikram Saxena 16 Jul '08

16 Jul '08

I am trying to use the circular_buffer template from Boost (version 1.35.0) with VS 2008 (msvc-9.0). I initially downloaded the compiled libraries from boostconsulting. However when I linked against them, I got a link error that (__imp___wassert not found )whenever I used an iterator. A search on the web revealed this problem seems to occur when the version of MSVC used to compile is different from the one used to link. I then decided to do a local compile using the basic bjam command with the toolset pointing to msvc-9.0. However I still get the same error; I have confirmed that VS is picking up boost libraries from the locally compiled location. The error does not happen in the Release mode. For the time being I am working around the problem by disabling assertion via a compile time flag which forces all boost asserts to (void)0. I will appreciate any thoughts on how to overcome this problem without disabling asserts. -Vikram

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[general] boost 1.35.0 library naming and bjam arguments priorities
by damny＠web.de 16 Jul '08

16 Jul '08

hi, for building boost 1.35.0 with bjam 3.1.16 and mingw gcc 3.4.5 on winxp sp2 i created a *.BAT-file like follows: @echo off SETLOCAL SET MINGW=C:\Development_Compiler\MinGW SET PYTHN=C:\Development_Compiler\Python25 SET BUILD=C:\Development_Libs\Boost_v1.35.0 SET path=C:\WINDOWS;C:\WINDOWS\system32;%MINGW%\Bin cls bjam.exe -a "-sTOOLS=mingw" "-sGCC_ROOT_DIRECTORY=%MINGW%" "-sPYTHON_ROOT=%PYTHN%" "-sPYTHON_VERSION=2.5" --link=static --runtime-link=static --threading=single --optimization=on --toolset=gcc --build-dir=%BUILD% --build-type=complete install ENDLOCAL this works well. but unlike boost 1.34.1 and bjam 3.1.15 [*] i get a lot of *.LIBs instead of *.A-files. is there a new/different library naming than this described in http://www.boost.org/doc/libs/1_35_0/more/getting_started/windows.html#libr… ? in spite of "--threading=single" i also get the "...-mt.lib"-files. why? covers "--build-type=complete" the single threading argument? thank you all daniel [*] i didn't review this, but the last build some months ago was okay :o) _______________________________________________________________________ EINE FÜR ALLE: die kostenlose WEB.DE-Plattform für Freunde und Deine Homepage mit eigenem Namen. Jetzt starten! http://unddu.de/?kid=kid@mf2

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Copy-on-write implementation
by Michiel Helvensteijn 16 Jul '08

16 Jul '08

I am looking for a simple way to implement copy-on-write classes. Several `copies' of an instantiation of such a class can coexist and share the same data in memory until someone changes their `copy' (calls a non-const member function). At that time, a deep copy is made and the change is only made in that one location. The deep copy is not needed, of course, if the instantiation has only one handle. All of this should be transparent to the user of the class. I think implementing such a class would be easier with a special class to inherit from and/or a useful set of macro's designed for this purpose. This seems like something that would (or should) exist in boost. Does boost provide something like this? If not, I will write it myself. But I'm still not sure how to approach it. I imagine shared_ptr would play a role, though. Any ideas? -- Michiel Helvensteijn

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Re: [Boost-users] Boost serialization: is there a way to perform selective read
by ari vol 16 Jul '08

16 Jul '08

The problem with this solution is that it is time consuming, to open file for a key, i would like to use the boost serializeation to improve time preformance. What is realy required is some mechanism, to identify an instance according to its key and only than read its data. Thus reading only the required instnace (accordig to its key) and not also the previous data at the file, someting like seek. I hoped that "XML boost" can supply someting like that, but could not find how. Thanks, -Ariella ----- Original Message ---- From: gchen <chengang31(a)gmail.com> To: boost-users(a)lists.boost.org Sent: Wednesday, July 16, 2008 9:43:56 AM Subject: Re: [Boost-users] Boost serialization: is there a way to perform selective read ari vol wrote: > Hey, > > I would like to know whether there is a way to preform selective read > using Boost serialization > <http://www.boost.org/doc/libs/1_35_0/libs/serialization/doc/index.html>, > thus reading serialized instance with its id/key. > > The implementation that i know is saving instances to a file and then > loading them all according to the saving order. Is there a way to read > only one selected instance from the file. > How about serializing objects separately? I mean instead of saving a object and its children objects into a big file, simply saving them into different files. _______________________________________________ Boost-users mailing list Boost-users(a)lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

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boost.program_options no throw
by Aljaz 16 Jul '08

16 Jul '08

Hello I've been wondering if there is no-throw version of boost::program_options::store , command_line_parser and basic_line_parser ? Many thanks in advance!

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[math/distributions/poisson] extract Poisson-distributed random variate?
by Michael Fuller 16 Jul '08

16 Jul '08

I've searched the Boost documentation and mail archive, but I can't find an example for extracting a random variate from a Poisson distribution. What I want to do is similar to extracting a variate from a uniform distribution, such as the C++ rand() function, which returns a single random variate on the range [0, RAND_MAX]. Is there a way to do something similar using the Poisson distribution with a given mean? For example, something like this: double n, lambda(0.30); //lambda is the mean of the Poisson n = poisson_rand(lambda); Thanks, Mike

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