November 2005 - Boost-users

[filesystem]Sorting based on equivalence information?
by Rush Manbert 14 Nov '05

14 Nov '05

Hi all, I have written a class around the glob_iterator class that W. Richard Johnson put into the file vault last year. My class finds all the paths and/or files matching a multi-level wildcard pattern. (i.e. the matching expressions may appear in more than one place, such as "/Users/*/MySource/??foo/*.cpp") I need to detect loops caused by links between directories, and I also want to detect multiple paths to the same file, and only keep one of them. The only method that I have come up with so far is to keep the paths that I have found in a collection and test each new path against all of them by calling equivalent() once for each collection member. Needless to say, this is a little slow when the number of files or directories becomes large. It could be faster if I only tested symlinks, but I think that the existence of hard links forces me to test everything. My first question: Can anyone suggest a better method of achieving the duplicates detection? My second question (This is probably directed at Beman Dawes): I read the code for equivalent(), and it seems like I could derive a class from path that would implement operator< in such a way that it sorted by the equivalence information, rather than by the path string. If I could sort the paths by their equivalence information, then I could binary search the collection when I look for duplicates. I would have to copy the code in equivalent(), which is an ugly thing to do, and I guess I would need to define all of the operators that are defined in path, since they are not virtual. Assuming that I did these things, though, does this sound like it's even valid? From the comments that I read in the equivalent() source, it seems that the file equivalence information can change, at least on a windows system. I guess I could create a handle_wrapper for each path that I add to the collection in order to keep the file from being moved while it's in the collection. Of course, I can't be the first person who has gone down this path, or the library would probably already support this sort of sorting. Is this just a stupid idea? Thanks, Rush

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problem using stream class when calling read function
by Hendra Hidayat 14 Nov '05

14 Nov '05

Hi, I have a problem when using stream class from iostreams library. I have created a device class say GDevice using iostreams::device_tag and iostreams::input_seekable tag. In GDevice I 've declared and implemented read function inside GDevice class. I also create a stream class let's say GStream which derived from iostreams::stream<GDevice>. The problem was occured when I created object from GStream and call GStream's read function directly to read say n bytes data. The GStream's read function invoked GDevice's read function not in n bytes data but always in 4096 bits. I dont understand where this number came from. I'm using boost 1.33, gcc compiler version 4.0.2 under x86-64 bit suse linux. Can somebody help me? Faithfully yours Hendra Hidayat Geophysical Lab. Natural Physics Dept. Sepuluh Nopember Institute of Tech. __________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.com

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DateTime parsing question
by Sean Rohead 14 Nov '05

14 Nov '05

I am trying to parse ISO datetime strings with millisecond resolution and the fractional seconds are being truncated. Am I doing something wrong in the following code? Thanks, Sean Rohead >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> #include <string> #include "boost/date_time/posix_time/posix_time.hpp" using namespace std; using namespace boost::posix_time; void main() { string dateString1 = "20051004T151801"; string dateString2 = "20051004T151801.123"; ptime timestamp1(from_iso_string(dateString1)); ptime timestamp2(from_iso_string(dateString2)); cout << timestamp1 << endl; cout << timestamp2 << endl; }

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Re: [Boost-users] [serialization]
by Kevin Carroll 14 Nov '05

14 Nov '05

> On Sun, 2005-11-13 at 16:02 -0800, Robert Ramey wrote: > > > Truth is, I don't even know how one goes about assigning a NaN or a > +/inf to floating/double variable !! Not an expert here like you guys, but how about: #include <limits> double x_NaN = std::numeric_limits<double>::quiet_NaN(); double y_PlusInfinity = std::numeric_limits<double>::infinity(); double z_MinusInfinity = -std::numeric_limits<double>::infinity(); ... Also, here is some concise info on IEEE standard floating point numbers available from the Internet: The following notes are reproduced from http://stevehollasch.com/cgindex/coding/ieeefloat.html Infinity The values +infinity and -infinity are denoted with an exponent of all 1s and a fraction of all 0s. The sign bit distinguishes between negative infinity and positive infinity. Being able to denote infinity as a specific value is useful because it allows operations to continue past overflow situations. Operations with infinite values are well defined in IEEE floating point. Not A Number The value NaN (Not a Number) is used to represent a value that does not represent a real number. NaN's are represented by a bit pattern with an exponent of all 1s and a non-zero fraction. There are two categories of NaN: QNaN (Quiet NaN) and SNaN (Signalling NaN). A QNaN is a NaN with the most significant fraction bit set. QNaN's propagate freely through most arithmetic operations. These values pop out of an operation when the result is not mathematically defined. An SNaN is a NaN with the most significant fraction bit clear. It is used to signal an exception when used in operations. SNaN's can be handy to assign to uninitialized variables to trap premature usage. Semantically, QNaN's denote indeterminate operations, while SNaN's denote invalid operations. The definition of NaNs, signed zero and infinity, and denormalized numbers from "IEEE Standard for Binary Floating-Point Arithmetic", ANSI/IEEE Standard 754-1985, Institute of Electrical and Electronics Engineers, August 1985., is reproduced below. In the following, 'S' stands for the sign bit, 'E' for the exponent, and 'F' for the fractional part. The symbol 'u' stands for an undefined bit (0 or 1). Type S (1 bit) E (11 bits) F (52 bits) signaling NaN u 2047 (max) .0uuuuu---u (with at least one 1 bit) quiet NaN u 2047 (max) .1uuuuu---u negative infinity 1 2047 (max) .000000---0 positive infinity 0 2047 (max) .000000---0 negative zero 1 0 .000000---0 positive zero 0 0 .000000---0 Kevin Carroll

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Boost.MultiArray + iterators
by Dennis Zickefoose 14 Nov '05

14 Nov '05

I have a simple two dimensional multi_array that I am trying to copy a row out of. This works, but I get a warning about a type conversion that I would like to get rid of. Example: boost::multi_array<double, 2> array(boost::extents[42][42]); std::vector<double> row(array[0].begin(), array[0].end()); This produces the following warning in VC++ 7.1: c:\Boost\include\boost-1_33\boost\multi_array\iterator.hpp(149) : warning C4244: '+=' : conversion from 'boost::detail::multi_array::array_iterator<T,TPtr,NumDims,Reference>::difference_type' to 'boost::detail::multi_array::array_iterator<T,TPtr,NumDims,Reference>::index', possible loss of data This is followed by a long string of support messages that ultimately point to the vector initialization. Yet the vector is successfully initialized with the range of values I expect. So what am I doing wrong here? I understand that [array.begin(), array.end()) is actually a range of sub-views, rather than a range of values...is this a side effect of this distinction? At the moment, I have replaced that with &array[0][0] to avoid the warning, but if possible I would like to go with the more reliable iterator interface in the future. Any suggestions/advice would be greatly appreciated. DZJr

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Desperately in need of help!
by Marcus Krantz 14 Nov '05

14 Nov '05

Hi all! I have an application which uses STLport 5.0.0, libtorrent (which in turn uses Boost). What I have done is that I have compiled the boost libraries for msvc7.1-stlport. I only uses three, i.e. filesystem, date_time and thread. My boost version is 1.33.1 So the problem occurs when my application is linking. Then I get a lot of LNK2005 link errors. I have no problems with compiling my code and use the boost libraries it's only when I'm about to link it fails. The errors says, in general, that a lot of things already are defined in libboost_xxx_mt-sp... I guess that if I post some of my errors it will be easier for those who wants to help me :) So here we go... 1. msvcprtd.lib(MSVCP71D.dll) : error LNK2005: "public: class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > & __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::operator+=(char const *)" (??Y?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAEAAV01@PBD@Z) already defined in libboost_filesystem-vc71-mt-sp-1_33_1.lib(path_posix_windows.obj) 2. msvcprtd.lib(MSVCP71D.dll) : error LNK2005: "public: class std::basic_string<unsigned short,struct std::char_traits<unsigned short>,class std::allocator<unsigned short> > & __thiscall std::basic_string<unsigned short,struct std::char_traits<unsigned short>,class std::allocator<unsigned short> >::erase(unsigned int,unsigned int)" (?erase@?$basic_string@GU?$char_traits@G@std@@V?$allocator@G@2@@std@@QAEAAV12@II@Z) already defined in libboost_date_time-vc71-mt-sp-1_33_1.lib(greg_month.obj) 3. msvcprtd.lib(MSVCP71D.dll) : error LNK2005: "public: char __thiscall std::basic_ios<char,struct std::char_traits<char> >::widen(char)const " (?widen@?$basic_ios@DU?$char_traits@D@std@@@std@@QBEDD@Z) already defined in libboost_thread-vc71-mt-sp-1_33_1.lib(once.obj) 4. msvcprtd.lib(MSVCP71D.dll) : error LNK2005: "public: class std::basic_ostream<char,struct std::char_traits<char> > * __thiscall std::basic_ios<char,struct std::char_traits<char> >::tie(void)const " (?tie@?$basic_ios@DU?$char_traits@D@std@@@std@@QBEPAV?$basic_ostream@DU?$char_traits@D@std@@@2@XZ) already defined in libboost_thread-vc71-mt-sp-1_33_1.lib(once.obj) I would really appreciate if anyone could help me out here. Since I am new to C++ etc. I have major difficulties in intepreting the error messages. Best regards Marcus Krantz

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vc-8_0-stlport
by Slava Tutushkin 14 Nov '05

14 Nov '05

Does anybody know if there are any plans about adding toolset support for Visual Studio 2005 with STLPort? In fact, I tryed to compile Boost 1.33.1beta using vc-8_0 toolset, but with STLPort installed. It was almost succeed not counting incorrect libraries naming (without -p- suffix in filenames). Slava Tutushkin mailto:aloner@aloner.ru

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Example error for boost::numeric_cast
by Daniel Krügler 14 Nov '05

14 Nov '05

Hello! The example for boost::numeric_cast contains documentation, which clearly is wrong and stumbles the reader. On http://boost.org/libs/numeric/conversion/doc/numeric_cast.html#numeric_cast we have the lines unsigned long l=std::numeric_limits<unsigned long>::max(); // This works, because unsigned integral types cannot cause overflow. unsigned char c=numeric_cast<unsigned char>(l); which contradict the behaviour and the range checking logic presented on http://boost.org/libs/numeric/conversion/doc/converter.html#rchklogic Btw.: Further on the #include directive, namely #include <boost/numeric_cast.hpp> should be corrected to #include <boost/numeric/conversion/cast.hpp> Greetings from Bremen, Daniel Krügler

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intrusive_ptr feature request for constructor
by Bruno Martínez 13 Nov '05

13 Nov '05

Hi. intrusive_ptr's constructor takes an bool to signal whether the refcount should be initially incremented or not. The default is true. I find that the default is different for different types, so I propose to add a hook to specify the policy for each type. At first I thought to do this with traits, but now I think a function is better because this doesn't need to be compile-time and a function overload works fine with ADL. I'm no expert in this, so maybe I'm mistaken somewhere. What I propose is to add: namespace boost { template <class T> bool intrusive_ptr_add_ref_at_construction(T*) { return true; } template<class T> class intrusive_ptr { intrusive_ptr(T * p, bool add_ref = intrusive_ptr_add_ref_at_construction((T*)0)): p_(p) { if(p_ != 0 && add_ref) intrusive_ptr_add_ref(p_); } ... } } then I can do bool intrusive_ptr_add_ref_at_construction(MyType*) { return false; } What do you think of this feature? Regards, Bruno

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Documentation question. Format and lexical_cast
by Drumheller, Michael 13 Nov '05

13 Nov '05

There seems to be some considerable overlaps in functionality between boost::lexical_cast and boost::format, yet, as far as I can tell, the documentation pages for each does not mention the other. Is this intentional, or would anyone agree that a doc fix would be in order? (Needless to say, if so, I would be happy to help with it.) Thanks, Michael D.

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