February 2004 - Boost-users - lists.preview.boost.org

boost::shared_ptr and stl algorithms
by Bill Eidson 15 Apr '05

15 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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about license
by Marleny Rafferty 01 Apr '04

01 Apr '04

Hi- I am considering using boost in my applications, but I have a question about the boost license at http://www.boost.org/LICENSE_1_0.txt . It says (edited) "Permission is hereby granted, free of charge, to ... use [and] reproduce ... the Software". It also says that any derivative works must also have the same license grant. If my application uses boost libraries unchanged, is it considered a derivative work? If so, does that mean that if I distribute my compiled software, I must allow free of charge use and distribution? Thanks. -- Marleny

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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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Solaris and thread_resource_error
by Peter Jones 23 Mar '04

23 Mar '04

On Feb 1 of this year Baptiste Lepilleur posted a status report for Boost 1.31.0 Release candidate 2 on Solaris and AIX. It was mentioned that "boost.thread is now systematically failing with 'thread resource error'". I am experiencing the same thing on Solaris 8, with GCC 3.3.2 (GNU binutils) and Boost 1.31.0. Has anyone looked into this yet? If not, I am willing to track down what line in Boost.Threads is throwing thread_resource_error(). -- Peter Jones [unix;vi;crypto;c++;4wd] (http://pmade.org) PGP [5137 173E 5BFA 8C63 8982 F035 FDBB 1636 7D69 C63F]

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Has mailing list 'from' address changed?
by Steve Folly 28 Feb '04

28 Feb '04

I'm not catch boost-users digest anymore with my mail rules? Vol 129 issue 3 from lists.boost.org, has a date stamp of 17:01:03. I've received a second copy from www.osl.ie.edu at 17:01:50. Is this a permanent change? -- Regards, Steve.

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Re: Iterator adaptor interoperability
by Kris Braun 28 Feb '04

28 Feb '04

Dave Abrahams wrote: > Your best bet is to write an type generator: > template <class Iterator> > struct simple_iterator > { > typedef boost::transform_iterator< > do_nothing< typename Iterator::value_type > > , Iterator > > type; > }; Thank you for the quick and clear reply! I'm now having a very similar problem with a slightly more complicated example (that builds on the first): template< class Iterator > struct harder_iterator { typedef simple_iterator< Iterator >::type inner_type; typedef boost::indirect_iterator< inner_type > type; static type Create( const Iterator& iter ) { return type( inner_type( iter ) ); } }; This "composite" iterator not only has problems with comparison, but assignment from non-const to const as well. Is there a way to handle this case? Thanks, Kris __________________________________ Do you Yahoo!? Yahoo! Mail SpamGuard - Read only the mail you want. http://antispam.yahoo.com/tools

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building boost 1.31.0
by Greg Silverman 27 Feb '04

27 Feb '04

Hi, I have not been able to build version 1.31.0. I run bjam -sTOOLS=gcc-nocygwin Basically, I get a lot of undefined references from the linker. The linker cannot find "cpp_main", "init_unit_test_suite", and, so on. It seems to be a problem with the testing, regression testing, unit testing, etc. Greg Silverman Northrop Grumman San Jose, CA

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lambda / boost usage questions
by Luis De la Parra 26 Feb '04

26 Feb '04

hello, I don't have much experience with boost, so I'm having problems getting boost lambda to work...hope someone here can point me in the right direction. I have: class Song {public: string artist( ) const { return m_artist } string title( ) const { return m_title } private: string m_artist, m_title; } typedef boost::shared_ptr<Song> pSong; vector<pSong> c; and I am trying to use lambda to find a song in c which matches a certain artist and title...something like iterator it = find_if( c.begin(), c.end(), something ) but I havn't figured out what "something" should look like I've tried find_if(begin(),end(), (_1->artist() == "a1" && _1->title = "t1" ) ); but the compiler -- or I =) -- doesn't seem to know the type of _1 --> error: base operand of `->' has non-pointer type `const boost::lambda::lambda_functor<boost::lambda::placeholder<1> >' If I try it = find_if(begin(),end(), boost::bind(&Song::artist,_1) == "a1" ); it fails because "_1" is ambiguos (defined as lambda/placeholder and boost/arg ) using boost::lambda::bind (and not including the "normal" bind ) gives a bunch cryptic errors... I've tried several other variants with lambda / lambda::bind / boost::bind but I havn't figured it out... can anyone help me out? I'd also like to know what's the difference between boost::bind and boost::lambda::bind ? Also... is there a way to know when a lambda object is going to be constructed?, it's probably just that I don't know much about the BLL, but in cases where you have several nested lambdas and binds, I'm not sure which lambda objects will get constructed. regards, luis

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bug in numeric_cast<unsigned long>, <unsigned char>, and <unsigne d int> in gcc 3.3.2
by King, William D 26 Feb '04

26 Feb '04

Hello, I am seeing a bug that the regression tests miss for numeric_cast<unsigned long> with gcc 3.3.2. Specifically, the following code is throwing an exception: double small_value = 1.25; unsigned long l=0; l = numeric_cast<unsigned long>(small_value); // throws exception! unsinged char c=0; c = numeric_cast<unsigned char>(small_value); // throws exception! I am under the impression that numeric_cast is supposed to accept losses of precision (by truncating the fractional values), and to throw exceptions only if there is a range or sign error. Is this so? This error happens only when I try to cast a value with a non-zero fraction; i.e. 1.25 breaks but 1.0 is fine. It only occurs for unsigned types -- signed int, char, and long appear to work correctly. I have found the same incorrect behavior with gcc 3.3.2 on both solaris and linux. Using sunpro on solaris, the same code runs correctly. The regression tests don't catch this, since they only test numeric_cast with integral values 1 and LONG_MAX. Any ideas? It looks like a compiler problem to me. Davis King william.d.king(a)bankofamerica.com

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