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boost::lambda how to question
by Eric Twietmeyer 25 Aug '03

25 Aug '03

Hello, I'm been having great fun getting to know and starting to use the lambda library over the past month or so. I can't believe how well the optimizing compiler I have (Vc7.1) is able to convert these lambda expressions used in for_each or find_if into tight loops. However, there I things I'm certain are possible, but I haven't been able to figure out. More examples of using the library than are found in the doc would be extremely useful. For instance, how do I do the equivalent of the following using a single for_each with suitable lambda expression as operator? using namespace boost::lambda; std::vector<int> vec1; std::vector<int> vec2; struct tOp { std::vector<int>& m_vec; tOp( std::vector<int>& vec ) : m_vec( vec ) {} void operator()( int entry ) { std::vector<int>::iterator it = std::find_if( m_vec.begin(), m_vec.end(), _1 == entry ); if ( it != m_vec.end() ) m_vec.erase( it ); } }; // How to use lambda expression here for third arg? std::for_each( vec1.begin(), vec1.end(), tOp( vec2 )); Basically, I have two lists (vectors) that overlap. I want to erase all elements from the one vector from the other vector, i.e. determine if the element from vec1 exists in vec2, and if so erase it from vec2. If this is possible and relatively straight forward using a lambda expression, I would love to see an example. Thanks in advance, Eric Twietmeyer PS It looks like something of this sort can be done with std::set_difference if one outputs into a third vector, but for argument's sake, let's assume I don't want to introduce a third vector. --------------------------------- Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software [Non-text portions of this message have been removed]

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boost.thread, DEC C++ (OpenVMS)
by Johan Nilsson 25 Aug '03

25 Aug '03

Hi, I've just tried to compile boost.thread under OpenVMS and got it working mostly fine, with a few quirks. I'm using Boost 1.30.2 and DEC C++ 6.5 under OpenVMS Alpha 7.1-1H1. OpenVMS provides a compliant(?) pthreads implementation. Note that I did _not_ use Boost.jam (I did try, but couldn't get it going). Compiling the .cpp files under BOOST_ROOT/libs/thread/src works pretty fine, once having defined BOOST_HAS_THREADS, BOOST_HAS_PTHREADS and BOOST_HASTIMEOFDAY on the compiler's commandline. But not for tss.cpp - I get the following error: ------------------------------------------------------------------------- res = pthread_key_create(&m_key, cleanup); .....................................^ %CXX-E-INCOMPATIBLEPRM, argument of type "void (*)(void *)" is incompatible with parameter of type "void (*)(void *) C" at line number 192 in file DISK$USER1:[COMMON.BOOST.LIBS.THREAD.SRC]TSS.CPP;1 ---------------------------------------------------------------------------- --- After some digging around I found out that the error only appears when using the compiler switch "/standard=strict_ansi", which is what I'm using all the time. Now to me it looks like the DEC C++ compiler believes that name mangling isn't the only thing that differs between "C" and "C++" linkage - does anyone here have any comments on that? See below for a small example (and possible way to work around this in the boost.thread implementation): ------ sample.cpp ------- extern "C" { typedef void (*c_linkage_cb_t)(void*); void c_linkage(void (*pfn)(void*)); } inline void cpp_linkage_using_c_typedef(c_linkage_cb_t pfn) { c_linkage(pfn); } inline void cpp_linkage(void (*pfn)(void*)) { c_linkage(pfn); } ---------------- end sample.cpp ------------------- And here's the output from the compiler: $ cxx /standard=strict_ansi t.cpp c_linkage(pfn); ..................^ %CXX-E-INCOMPATIBLEPRM, argument of type "void (*)(void *)" is incompatible with parameter of type "void (*)(void *) C" at line number 19 in file DISK$USER1:[COMMON.BOOST.LIBS.THREAD.SRC]T.CPP;11 I don't know if this is a compiler bug or not, but in order to work around this in boost.thread, wouldn't it be feasible to provide a similar fix to the tss implementation to avoid the compilation problem - e.g. ---- tss.hpp ----- ... extern "C" { typedef int (*pthread_<something>_cb_t)(void*); } ... class tss { ... ... tss(pthread_<something>_cb_t cb) ... --- end tss.hpp ---- Comments appreciated // Johan

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out of core property map and constant property map
by Joel Young 24 Aug '03

24 Aug '03

Has anyone created property maps that operate out of core? either against a database or a flat file? Would you like to share? Also has anyone created a property map that, once create returns a constant value for all queries (writable is nice, it doesn't do anything with the write of course)? This might be useful for compactly representing constant edge capacities. Finally, an out of core BasicMatrixConcept implementation for use with all-pairs shortest path on largish (n=1.6M, e=10*n) graphs would be handy. Thanks, Joel

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graph adapter from bidirectional to undirected
by Joel Young 24 Aug '03

24 Aug '03

Has anyone created a graph adapter to make a bidirectional graph appear as an undirected graph? If not, is the difficulty in making an edge iterator across both the in and out links? I particular I would like to compute a weak connected components on a bidirectional graph. So if you have a modified connected components alg for that it would be great. Thanks, Joel

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bjam exe for cygwin on win98
by Fernando Cacciola 23 Aug '03

23 Aug '03

Hi, The link on http://www.boost.org/tools/build/index.html#Jam states that bjam executables can be found at: http://sourceforge.net/project/showfiles.php?group_id=7586 but I don't know which of the bjams there is an executable for cygwin on win98 TIA Fernando Cacciola

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Parent-Child Object Relationships with shared_ptr
by Martin Ecker 23 Aug '03

23 Aug '03

Hello, I've been thinking of switching one of my projects to use boost::smart_ptr and I'm currently investigating this option a bit. In my project there are a lot of cases where an object acts as factory/parent object to create other child objects. These child objects must keep the parent object alive as long as one of them still exists. Or in other words, even if the client does not hold a pointer to the parent object anymore, the parent must continue to exist as long as there is still a child object. Also the child objects sometimes need to have access to the parent object that created them. Therefore, I thought I'd have them hold a shared_ptr to the parent object. So the situation looks something like this, where both Parent and Child objects are only allocated on the heap and should only be passed around as shared_ptr. class Parent { public: boost::shared_ptr<Child> CreateChild() const { boost::shared_ptr<Child> child(new Child(this)); return child; } }; class Child { friend class Parent; protected: Child(const boost::shared_ptr<Parent> parent) : m_parent(parent) {} private: boost::shared_ptr<Parent> m_parent; }; As far as I understand it I can't do new Child(this) because Child expects a shared_ptr, so I'd have to derive Parent from enable_shared_from_this. However, in my project there are a number of classes in a rather complicated class hierarchy to which the above pattern applies and I'd thus like to avoid having to (multiply) derive them from enable_shared_from_this. Is there another, possibly better way of achieving what I want to do (keep the parent alive as long as there are still child objects) that I haven't discovered yet? Or do I really have to derive all these classes from enable_shared_from_this? Do I have to derive each class in a class hierarchy from enable_shared_from_this, if each of them needs to give out a shared_ptr-managed this pointer? Thanks for any help, Martin

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newbie trying to make a dll
by schmitty9812003 22 Aug '03

22 Aug '03

This is my very first experience with Boost. I am actually trying to use the SDTS++ libraries (if anyone is familiar with them) which use Boost. Anyway, I successfully built the library using the Jamfile that was included with the download which looks something like this: lib sdtsxx : ... : <include>$(BOOST_ROOT) <include>$(TOP) <include>. <include>$(TOP)/Windows # to get bogus "unistd.h" <rtti>on <exception-handling>on <msvc><*><cflags>-TP # force to compile as C++ <gcc><*><cflags>"-x c++" # force to compile as C++ <gcc><*><define>VECTOR_ITERATOR_POINTER_NOT_EQUIVALENT : debug release ; However, what I need is for the library to be a dll. So I changed the Jamfile to look something like this: SOURCES = ...; dll sdtsxx : $(SOURCES) : <include>$(BOOST_ROOT) <include>$(TOP) <include>. <include>$(TOP)/Windows # to get bogus "unistd.h" <rtti>on <exception-handling>on <msvc><*><cflags>-TP # force to compile as C++ <gcc><*><cflags>"-x c++" # force to compile as C++ <gcc><*><define>VECTOR_ITERATOR_POINTER_NOT_EQUIVALENT : debug release ; Unfortunately this gives me linking errors like this: sb_Accessor.obj : error LNK2001: unresolved external symbol "public: class boost::filesystem::path __thiscall boost::filesystem::path::branch_path(void)const "(? branch_path@path@filesystem@boost@@QBE?AV123@XZ) Now I don't know that this is a Boost problem or if I should go to the SDTS people. Since the unresolved externals are from the Boost libraries I figured it was a Boost issue. So am I doing something wrong with the Jamfile, or is there a problem with Boost? Or is it something completely different? Oh, I'm using msvc on an XP machine, if that matters... -ms

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Compiler help
by Henry ?? 22 Aug '03

22 Aug '03

I'm trying to try out the thread library on HP-UX and SGI Irix using GNU GCC and have not been able to run them succesfully. I noticed that on the "Boost Regression Tests" the compiler Status for both my platforms and compilers have failed with messages similar to what I am getting. Do I have any options or is it just not possible to try the thread library for my systems. Thanks

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request: complete list of output files of build?
by Li Lirong 22 Aug '03

22 Aug '03

Is it possible for the boosters to provide a complete list of the lib and dll files (include debug and release versions) that the build system produces? Thanks. Best regards, Lirong

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RE: [Boost-Users] Re: Re: boost::intrusive_ptr and Managed C++?
by Ferdinand Prantl 22 Aug '03

22 Aug '03

Hi Holger, > -----Original Message----- > From: Holger Grund [mailto:yg-boost-users@gmane.org] > Sent: Thursday, August 21, 2003 14:50 > To: boost-users(a)yahoogroups.com > Subject: [Boost-Users] Re: Re: boost::intrusive_ptr and Managed C++? > > > "Ferdinand Prantl" <ferdinand.prantl(a)ixos.de> wrote > > > The second option (as Holger says) is to make a simple facade to the > c++ > > library (all you might use), which will not have templates (here > smart > > pointers) on the interface, and to use this facade instead. > > > Did I say that? Anyway, I absolutely agree. Oops, sorry, I thought a bit further... :-) > > I just want to point out that IMHO the best solution is to > _not_ export instrusive_ptr_add_ref and _release. If you do > new and delete are called from different modules which works > only if the same CRT instance is used. And that works only if > both link against the exact same version of the CRT dll (that > is both linking against a static CRT still yields to > instances => two heaps => error). The generally safest solution yes, but not always the simpliest and most understandable. With a pile of C++ libraries with templates and STL on interface to use, I would not be very keen on writing facades for each and every... Every such a wrapper also increases the complexity of the solution. > > While we're at it, it's almost always a bad thing to export > classes or functions that rely on classes from a DLL. DLLs > are a run time concept. They don't have any clue which > version of the compiler a consumer is built with. > > E.g. say you export a function > void foo( std::string& s ) > { > s = "Hello World!"; > } Oh yeah, that's terrible constraint - if releasing binary library, one must support more compilers and also create different binary names (e.g. boost_regex). It is not needed if you release sources of the library (not the case of commercial APIs). If STL is widely used in the dependency tree of libraries, it is a pity to abandon it from their interfaces, building special marshalling structures or serializing into streams or return pointers. In this situation I broke the general recommendation (no templates on iface), preferred simplier solution and went on with STL on interfaces. It is cheaper and runs faster too. I moved the task of creating a facade without STL to the person, who needs it. As long as everybody are happy with usage of the same STL on interface, such a facade does not need to be borned (for managed .net assemblies it is also not necessary)... > > The DLL is built with the version A of the compiler and STL > and the consuming application is built with version B. There > is no guarantee for a binary compatibility between the two > version. And indeed the code above will break if version 6 & > 7 of VC are used (The former used a COW scheme while the > second uses a short string optimization). This must not happen. It is responsibility of the build configuration to use the belonging import libraries. It can be checked and forced by pragmas in msvc. Ferda > > Also, do note that the DLL CRT now supports side by side sharing. > > While I am in rant mode the catch(...) thing is also a very > bad idea in VC. This currently catches (this will be fixed in > 8.0) structured exception that are not C++ exception. That > way serious error conditions are silently ignored. > > -hg > > > > > ------------------------ Yahoo! Groups Sponsor > ---------------------~--> Buy Ink Cartridges or Refill Kits > for Your HP, Epson, Canon or Lexmark Printer at Myinks.com. > Free s/h on orders $50 or more to the US & Canada. > http://www.c1tracking.com/l.asp?cid=5511 > http://us.click.yahoo.com/l.m7sD/LIdGAA/qnsNAA/EbFolB/TM ---------------------------------------------------------------------~-> Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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