August 2006 - Boost-users - lists.preview.boost.org

[Format] Why boost::format doesn't work with /vd2 compiler option?
by SMART_n 22 Aug '06

22 Aug '06

Hello. I have a project in Visual Studio 2005. This project uses GtkMM library and it's necessary to use /vd2 compiler option. The problem is that Boost::format doesn't work(raise exception) with this option. What can i do? Is it possible to use boost::format with this compiler option?

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bcbboost 0.5 released
by Nicola Musatti 22 Aug '06

22 Aug '06

Hallo, I just released version 0.5 of bcbboost, a set of patches that enable use of the Boost 1.33.1 libraries with Borland's BCB2006. This is likely to be the last release to be based on this combination of libraries and compiler. As 1.34 will include all the patches included here, I don't expect to issue further releases before a new version of BCB comes out. You can download it from here: http://prdownloads.sourceforge.net/bcbboost/bcbboost-1_33_1-5_8_2-0.5.zip?d… Please post any bug report, suggestion, request for clarification to the project trackers on its SourceForge site: http://sourceforge.net/projects/bcbboost/ Cheers, Nicola Musatti

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SIGABRT (Abort) On Debian with boost::filesystem::path append
by Eric Hill 21 Aug '06

21 Aug '06

Does anyone have any suggestions on how I can fix/diagnose/troubleshoot this little problem? 11 std::cout << "Parsing folder " << folder_name << std::endl; (gdb) n Parsing folder testing 12 boost::filesystem::path folder(folder_name, boost::filesystem::native); (gdb) n 13 boost::filesystem::path message_to = folder / ".to"; (gdb) n Program received signal SIGABRT, Aborted. 0x4040583b in raise () from /lib/tls/libc.so.6 (gdb) TIA, Eric

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[type_traits] Why there is no recursive_const trait?
by Ovanes Markarian 21 Aug '06

21 Aug '06

Hello, I am just wondering why boost does not provide recursive_const type trait? The application would be for Example: recursive_const<T***>::type same as: T const *const *const *const Are there any reasons not to provide this? With Kind Regards, Ovanes Markarian

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boost::bind and member template functions
by Matt Schuckmann 21 Aug '06

21 Aug '06

I can't seem to make boost::bind work with a member template function and it seems like is should. The following won't compile with MSVC 7.0, struct Test_t { template<typename T> void testV( int i, std::vector<T>& b ) { b.push_back( static_cast<T>(i) ); } char m_c; }; void MyTest() { int i(1); Test_t t; std::vector<long> v; boost::bind( &Test_t::testV<long>, t, _1, v )(i); } I get a whole bunch of wrong number of arguments errors. I tried the boost::bind<void> variation and that also won't compile, just with a little different error of the form "cannot convert parameter 1 from 'void (int,std::vector<_Ty> &)' to 'boost::type<T>'" If testV is just a regular template function, not a member of a class or struct, it works fine. Anybody have any idea how to make this work? Thanks, Matt S.

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Header file granularity policy?
by Scott Meyers 21 Aug '06

21 Aug '06

Some Boost libraries, such as SmartPtr and Variant, offer a single header with declarations for all library functionality as well as a set of headers for subsets of functionality. For example, smart_ptr.hpp declares all of shared_ptr, shared_array, weak_ptr, scoped_ptr, scoped_array, and intrusive_ptr. If I don't want all these declarations, I can use more specific headers, e.g., shared_ptr.hpp or scoped_array.hpp. Such libraries allow me to choose between the convenience of a single comprehensive header or the precision of multiple targeted headers. Other libraries seem to offer only the collection of targeted headers. For example, FileSystem offers five headers, but there doesn't seem to be a comprehensive filesystem.hpp. Similarly, Lambda seems to offer only targeted headers; there doesn't seem to be a single "declare everything in Lambda" header. (There is a lambda.hpp, but it's not comprehensive, e.g., it doesn't declare Lambda's bind.) I find that this kind of inconsistency among libraries degrades my experience as a Boost user, especially when I'm first learning to use a library. More than once I've spent time puzzling over a compilation error, only to discover that my mistake was not including a needed header. (I seem to make this error most commonly when using Lambda.) Is there some kind of Boost convention or policy on whether a library should offer a comprehensive "declare everything in the library" header in addition to more targeted headers? Thanks, Scott

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Compile 32 bits on 64 arch how-to ?
by david v 21 Aug '06

21 Aug '06

Hello, I would like to compile boost on 64 opteron arch but create the libraries in 32 bits mode (using -m32 cxxflags). The reason for that is that i have quite a lot libraries compiled in 32 that i can't port for the moment to 64. I'm not sure how to do that. I read about modifying user.hpp usung the configure script and that is what i did but it still doesn't seem to compile with the -m32 compiler flag. Can anyone help me ?

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bind depending on the type
by Minkoo Seo 19 Aug '06

19 Aug '06

Hi list. I'm trying to find out the way to bind depending on the types in a lambda expression. Let's take the following as an example: #include <iostream> #include <vector> #include <numeric> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> using namespace std; using namespace boost::lambda; int main() { vector< pair<string, int> > subjects; subjects.push_back(make_pair("Math", 90)); subjects.push_back(make_pair("English", 86)); subjects.push_back(make_pair("Physics", 88)); subjects.push_back(make_pair("Biology", 97)); long total; total = accumulate(subjects.begin(), subjects.end(), 0, _1 + bind(&pair<string, int>::second, _2)); cout << "total score: " << total << endl; return EXIT_SUCCESS; } This is a simple score card application that computes the total score. As you can see, I've used bind in calling accumulate and that seems to be ugly. So, I modified the code as follows: #define get_score(p) (bind(&pair<string, int>::second, p)) .. total = accumulate(subjects.begin(), subjects.end(), 0, _1 + get_score(_2)); This seems to be pretty. But the problem is that this code depends on the fact that _1 is int while _2 is pair<string, int>. I don't know whether this is platform independent, and this code still seems to be weird anyway. So, what I want to do is write a function get_score that successfuly compiles and run the following: total = accumulate(subjects.begin(), subjects.end(), 0, get_score(_1) + get_score(_2)); I've tried my best only to fail. Could anybody write get_score functions for me? Thanks in advance. Sincerely, Minkoo Seo

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Convenience.hpp extension core drops on ~ (tilda)
by Bob J 19 Aug '06

19 Aug '06

I ran across a problem in the convenience extension function. If the filename happens to have the the tilda character in it the function core drops. I discovered the problem when a file named ~trash was inadvertently created in a data directory. After creation of that file the system started core dropping. After much debugging I narrowed the problem to the extension function and the ~trash file. I was able to replicate the problem by std::string filename = "~test.txt"; string ext = extension(filename); Does anyone know a work around or if there are any other gotcha characters in this function. Bob

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[SmartPointers] weak_ptrs, raw pointers, and cycles
by Scott Meyers 18 Aug '06

18 Aug '06

I've recently realized that I just don't get something. Cycles of shared_ptrs are bad, because they can lead to resource leaks. To break a cycle, we're encouraged to use weak_ptrs. Okay, but we could use raw pointers to break the cycle, too, and I can't see any advantage offered by the weak_ptr. If A uses a shared_ptr to B and B uses a weak_ptr to A, B's life will be shorter than A's (its destructor will be invoked from A's destructor and will run to completion before A's does), so there is no advantage to a weak_ptr being able to tell if it dangles. In this context, it never will. So it seems that using a raw pointer to break cycles has no disadvantage over a weak_ptr, and it's more efficient (i.e., smaller and faster). Clearly, I'm missing something. Can somebody please explain what it is? I understand that weak_ptrs have other uses (e.g., as observers), so my question is only about the advice to use weak_ptrs to break cycles. Thanks, Scott

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