January 2004 - Boost-users - lists.boost.org

boost::shared_ptr and stl algorithms
by Bill Eidson 14 Apr '05

14 Apr '05

std::vector< boost::shared_ptr<T> > TVec; I want to write a function object to run std::for_each. to do somework against members of T and accumulate results in functor. My attempts have failed in VC7 with memory errors in my operator() method. struct fo { bool operator()( boost::shared_ptr<T>& t ) { return true; } }; Thanks in advance bille

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Will libraries built on WinNT run on Win98? (MinGW)
by Reed Hedges 31 Mar '05

31 Mar '05

I know that Win98 is not really supported, but is there any chance that libraries (specifically thread and regex) that were build on WinNT using MinGW work on Win98 (in MinGW)? My guess is no, but has anyone tried it? thanks reed

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MultiArray questions
by Dr Mark H Phillips 24 Mar '04

24 Mar '04

Hi, I've recently found out about the existence of MultiArray and I am quite impressed! I was thinking of implementing something similar myself but now hopefully I don't have to! However I have a few questions that I'm hoping someone can answer. Question 1 ---------- In the user documentation there is an example which has some example code: for(index i = 0; i != 3; ++i) for(index j = 0; j != 4; ++j) for(index k = 0; k != 2; ++k) A[i][j][k] = values++; Why can't you change the != into <? Ie, do: for(index i = 0; i < 3; ++i) for(index j = 0; j < 4; ++j) for(index k = 0; k < 2; ++k) A[i][j][k] = values++; or can you? This would be more efficient I should think, and requiring that index types be ordered shouldn't be too onerous should it? Question 2 ---------- If I use the built-in "no-frills" C array type to represent a 2-dimensional array in row-major order, then I would access an element (i, j) by doing: a[ &a[0] + i*n + j ] where a is my m by n array. And if I wish to traverse a, in row-major order, I can do: for (int* ip=&(a[0]); ip<&(a[n*m]); ip+=n) { for (int* ijp=&(ip[0]); ijp<&(ip[n]); ++ijp) { visit(ijp); } } These are a very efficient ways of doing things, but it lacks somewhat in ease-of-generalization and in readbility. This is where the MultiArray library is useful. But do I lose in efficiency by going to MultiArray? Ie, in the simple case where base is 0, stride is 1, and when we traverse in row-major order, is the MultiArray library smart enough to do compile-time optimizations to generate code which is as efficient as the above? I am guessing that this sort of approach is what the Blitz++ library does?? Question 3 ---------- Is it possible to construct a new multi_array/multi_array_ref/const_multi_array_ref from an array_view by doing a deep copy of the view? A view is a nice way of looking at different parts of a MultiArray object in a readable way, but sometimes you might wish to turn this view into a more-efficiently represented object. Is this easy to do in the MultiArray library? Question 4 ---------- Sometimes you might have an object starts off being mostly accessed in row-major order, so you want a representation which works efficiently for this use. But down the track you might wish to change to mostly column-major access. Does MultiArray provide easy ways to transform from one underlying representation to another? Thanks, Mark Phillips.

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[Date-Time] Issues
by Andrew V. Bronnikov 02 Feb '04

02 Feb '04

Hello, All! When I was familiarized with the great Boost Library one of the most inspiring part of it was the Date-Time Library. Date and time issues are very important in our project related with time series, so I immediately started to read docs, and tried to incorporate the lib as it became possible for us. As usual, problems hadn't kept waiting... :) Issues: 1. why gregorian::date and posix_time::ptime have no default constructors (possibly initializing them into some special value - good candidates are not_a_date_time, neg_inf or local_time (see next issue))? Lack of default ctors doesn't allow direct use of date-time objects in tuples and other containers requiring default-constructible classes. 2. why special_values enum has no "local_time" (or "now") item? It seems "special" enough, and - more important - it allows to pass the "initialize as current time" directive as a time initialization policy in templates. 3. why date, ptime, durations have no setters for their components (days, hours, minutes etc)? I guess it related with validity checking issues - am I right, or there are some other reasons? 4. why hours(), minutes() etc are classes, not simple time_duration factory functions? What the another level of inheritance for? Consider using a time_duration in lambda expressions (e.g. in the Spirit semantic actions): posix_time::time_duration dt; .... rule<> hours = uint_p [var(dt) += posix_time::hours(_1)] This will not compile because hours() is not a function. Instead, I must use something like a lazy constructor: rule<> hours = uint_p [var(dt) += bind(constructor<posix_time::hours>(), _1)] but it looks not so short as before. And - surprise! - it doesn't compile too, just because of the next problem: 5. neither of date, ptime or time_duration defines operator+=(). What is the reason for denying it? It seems quite natural to have a set of assignment operators for date_time classes, isn't it? 6. it would be great if GDTL classes will support explicit/implicit conversion functions/operators from/to older standard types like a time_t etc. It will allow smoother transition from old libraries to the GDTL. Thanx for the great work anyway! With best regards, Andrew V. Bronnikov.

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Problems with boost build setup
by Michael Buksas 31 Jan '04

31 Jan '04

Hi all, I'm having newbie problems with linking against Boost libraries. Here's the situation: I can build the boost libraries without problem, and I'm using the default toolkit for my system, (Fedora Core 1) which is g++. Compiling is no problem, just linking. I can link the object files by hand, but not as part of using Boost.build. As a test, I grabbed an example program from the date_time library and it's corresponding build rule. This code compiles fine as part of Boost, but if I move it to my project space, I get linking errors. Here's my Jamfile: exe time_math : <lib>$(BOOST_ROOT)/build/boost_date_time time_math.cpp : <include>$(BOOST_ROOT) <define>BOOST_DATE_TIME_POSIX_TIME_STD_CONFIG ; and here's my Jamrules in the same directory: project-root ; path-global BOOST_ROOT : "/opt/boost-1.30.2" ; Here's the Jamfile from /opt/boost-1.30.2/libs/date_time/example/ exe time_math : <lib>../build/boost_date_time posix_time/time_math.cpp : <include>$(BOOST_ROOT) <define>BOOST_DATE_TIME_POSIX_TIME_STD_CONFIG ; And the environment variable is set: BOOST_BUILD_PATH=/opt/boost-1.30.2/tools/build When I run bjam from a clean build, here's what I get: gcc-C++-action bin/time_math/gcc/debug/runtime-link-dynamic/time_math.o gcc-Link-action bin/time_math/gcc/debug/runtime-link-dynamic/time_math bin/time_math/gcc/debug/runtime-link-dynamic/time_math.o(.gnu.linkonce.t._ZN5boost9date_time15month_formatterINS_9gregorian10greg_monthENS0_13simple_formatEE12format_monthERKS3_RSo+0x3a): In function `boost::date_time::month_formatter<boost::gregorian::greg_month, << edited for brevity >> In function `boost::date_time::month_formatter<boost::gregorian::greg_month, << edited for brevity >> collect2: ld returned 1 exit status export LD_LIBRARY_PATH g++ -g -o "bin/time_math/gcc/debug/runtime-link-dynamic/time_math" "bin/time_math/gcc/debug/runtime-link-dynamic/time_math.o" -Wl,-rpath-link,. ...failed gcc-Link-action bin/time_math/gcc/debug/runtime-link-dynamic/time_math... ...failed updating 1 target... So things are compiling, but not linking. I must not have the configuration for Boost.build correct, but I've tried everything I can think of. Any help would be appreciated. Thanks, Mike Buksas -- Michael Buksas -- michael(a)buksas.net -- www.buksas.net

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Properties in a subgraph
by Hugues Joly 30 Jan '04

30 Jan '04

Hi, I'd like to clarify a point about the graph properties accessed through a subgraph. According to the documentation of get(PropertyTag, subgraph& g): vertex and edge properties are shared by all subgraphs, so changes to a property through a local vertex descriptor for one subgraph will change the property for the global vertex descriptor, and therefore for all other subgraphs (c.f. boost-1.30.2/libs/graph/doc/subgraph.html). Here, I'm sending you a small program inspired by the boost-1.30.2/libs/graph/example/subgraph.cpp example. >From its behavior, it seems that: 1) A property value is not shared between the global descriptor and its corresponding local descriptors. 2) we need to initialize property values for each of the subgraphs. For example, if I set a name "A" for the global vertex descriptor A, that property is not seen through the corresponding local vertex descriptors. Is this a case of misuse or is it a bug? __________________________________________________________ Lèche-vitrine ou lèche-écran ? magasinage.yahoo.ca

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Re: [Boost-users] Using boost::format with Lambda expressions
by Shawn Church 29 Jan '04

29 Jan '04

Jaakko Jarvi (jajarvi(a)cs.indiana.edu) wrote: > Lambda and format don't play well together, I noticed :( > Here's a code that works however, with some explanation. > Not pretty. > > Best, Jaakko > ... > format f("%-10s|") ; > for_each(Foos.begin(), Foos.end(), > cout << ret<format&>(var(f) % bind(&foo::name, _1))); > > } > > // format defines operator% as a member, which takes precedence over > // % defined by lambda. Therefore one must make the format object to > // be a lambda functor. var does that. > // Var, however, cannot take a temporary object (it holds a reference to > // the wrapped object). That's why the variable f. > // ret<format&> informs lambda about the return type of formats % operator. OK, that is just what I was looking for, thanks!!! I tried all of those things but not in the right combination. Is there any resources (i.e. example programs or additional documentation) available for the lambda library. I have read through the test code already. Thanks,

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Using boost::format with Lambda expressions
by Shawn Church 29 Jan '04

29 Jan '04

I may be missing something simple here but I have tried everything I can think of and cannot get the following to work (simplified from a project I am working on): Given a class such as: class foo{ public: foo(const char* name): _name(name) {} const char* name() const {return _name.c_str();} private: std::string _name;}; I can do the following without any problems: std::vector<foo> Foos; ... for_each(Foos.begin(), Foos.end(),cout << bind(&foo::name, _1) << "|"); This prints a list of all the names in the vector of Foo objects by calling the Foo::name() method. It would be nice to be able to do something like the following: for_each(Foos.begin(), Foos.end(), cout << format("%-10s|") % bind(&foo::name, _1); I have tried everything I can think of including extending the return type deduction of the lambda library to include the "%" operator as used by format and binding directly to the basic_format::operator% method. In every case I get 40 or so compile errors explaining why my 30 character statement is wrong :-) Does anyone have an example of this usage that works? This is not a high priority as I can obviously just format the value returned by the Foo::name() method but it would be nice to have this technique available when the need arises. I adapated the code above from a test program that demonstrates the problem in detail. I can provide the test program if anyone is interested (just tell me what to do with it). Thankyou for any help you can provide, Shawn Church sl_church(a)sbc_global.net

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Storing vertex objects and edge objects in a BGL graph?
by Hugues Joly 29 Jan '04

29 Jan '04

Hi, I'd like to know if it's possible to create a BGL graph that uses custom-made classes for the nodes and the edges. While looking to your documentation, I came across the following: "Many graph representations (such as adjacency lists) do not store actual vertex objects, while others do (e.g., pointer-linked graphs)." (c.f. boost-1.30.2/libs/graph/doc/quick_tour.html) Is the pointer-linked graph implementation supplied from boost or do I have to create one and use external adaptation for using it with your library? Thanks in advance. __________________________________________________________ Lèche-vitrine ou lèche-écran ? magasinage.yahoo.ca

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1.31.0??
by Phil Hornby 28 Jan '04

28 Jan '04

Hi all, Just wondering when a release of 1.31.0 is planned for? Thanks... -- Phil "Requirements - what are they I just hack something together that does what I think they want" ;)

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