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

Two issues with lexical_cast
by Yuval Ronen 01 Feb '05

01 Feb '05

Hi. I'm probably just another one out of a million who make these remarks, but I found nothing in the documentation about them, so I'll mention them anyway. 1. lexical_cast(Source arg) takes the source argument by value. Why not by const& ? Calling lexical_cast(some_basic_string) now makes a copy of the source argument for no reason. 2. lexical_cast ignores trailing whitespaces, but not leading whitespaces. Meaning that int a = lexical_cast<int>("3 "); // three-space will work and return 3, but int a = lexical_cast<int>(" 3"); // space-three will throw. Why? There's no rationale here. Both cases should be treated in the same manner, and IMHO, that manner should be throwing. After a look at the code, it seems that the trailing-whitespace-ignore code ('stream >> std::ws' in line 151) was specifically added, so there was supposed to be a reason for this. But as I said, I believe this is wrong, at least as the default behaviour when converting a string to something else. Maybe some policies (IgnoreLeadingWhitespace, IgnoreTrailingWhitespace) can be added to control this? And again, I suppose I'm not the first to think of it... Thanks, Yuval

5 18

RE: [Boost-users] Rationale for intrusive_ptr?
by Nat Goodspeed 01 Feb '05

01 Feb '05

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org [mailto:boost-users- > bounces(a)lists.boost.org] On Behalf Of Brian Neal > Sent: Monday, January 31, 2005 7:34 PM > To: boost-users(a)lists.boost.org > Subject: [Boost-users] Rationale for intrusive_ptr? > > Hi, I need some help understanding when and why you > would want to use intrusive_ptr. Does someone have an > example? I didn't get much out of the current > documentation for it. Thank you. [Nat] Consider: class MyClass; void some_func(const boost::shared_ptr<MyClass>& ptr); class MyClass { public: void process() { // BAD THINGS HAPPEN! some_func(boost::shared_ptr<MyClass>(this)); } }; In our current project, we've been bitten more than once :-( by situations that are analogous but less obvious. Inside a member function, you don't have a shared_ptr<MyClass>, you only have a dumb MyClass* 'this' pointer. But if MyClass is managed with smart pointers, you probably have processing functions that accept only a smart pointer to MyClass. A natural-looking data conversion is easy to code and makes the compiler happy. What happens, though, is that when you instantiate a new shared_ptr<MyClass> from your dumb 'this' pointer, it gets a whole new refcount object! In the example above, the temporary shared_ptr<> goes away as you're about to exit MyClass::process() -- which makes its spurious refcount go to 0 -- which deletes the MyClass instance in question, even though there are probably still existing shared_ptr<MyClass> references to the same instance lying around! (e.g. the one with which you called the process() method) We now use intrusive_ptr almost exclusively (vs. shared_ptr). We limit its intrusiveness by deriving all subject classes from an intrusive_base we wrote, which contains the refcount we use and a couple of methods. This practice has cut down considerably on bizarre crashes.

1 0

implicitly_convertible<a,b>
by Benjamin Schmeling 31 Jan '05

31 Jan '05

Hi, I have exposed a bigint class which has no constructor for long_ . I added an additional constructor by defining .def("__init__", make_constructor(bigint_constructor)) This works fine. Now I want to use the implicitly_convertible function which expects from the class to have an constructor which takes the first argumen (in this case a long_) I used implicitly_convertible<boost::python::long_ ,bigint> but now the problem is that the original c++ class has no such constructor, but the wrapped class. How can I make him use my new constructor in implicitly_convertible? Benjamin

1 0

Compile problems with multi_index on CW 9.3 (mac)?
by Marshall Clow 31 Jan '05

31 Jan '05

I'm trying to use boost::multi_index for the first time, and I'm getting odd compile errors. I have a class with two "keys", a text one and a numeric one, and I want to have two indices into the collection. So, I tried several things, and all of them get the same error: 'index_class' is not a member of class 'boost::multi_index::ordered_unique<boost::multi_index::identity<Foo>, boost::multi_index::detail::null_arg, boost::multi_index::detail::null_arg>' (and then an amazing cascade after that) Here's the basic idea: typedef boost::multi_index_container < Foo, boost::multi_index::indexed_by < boost::multi_index::ordered_unique < boost::multi_index::identity < Foo >, LessThanNumeric >, boost::multi_index::ordered_unique < boost::multi_index::identity < Foo >, LessThanText > > > Foo_; where LessThanNumeric (and LessThanText, too) looks like this: struct LessThanNumeric: std::binary_function< Foo, Foo, bool > { bool operator () ( const Foo& x, const Foo& y ) const { return x.NumericKey () < y.NumericKey (); } }; My source is at <http://www.idio.com/misc/mi-test.cpp> Anyone got any tips? Thanks! -- -- Marshall Marshall Clow Idio Software <mailto:marshall@idio.com> It is by caffeine alone I set my mind in motion. It is by the beans of Java that thoughts acquire speed, the hands acquire shaking, the shaking becomes a warning. It is by caffeine alone I set my mind in motion.

2 1

boost::filesystem -- "Aborted"
by matthias 31 Jan '05

31 Jan '05

Hi, I am currently writing a gtkmm component which acts as a file browser, much like a small filemanager which can be embedded in gtkmm applications as a scrolled window. I have just rewritten the component to use the boost::filesystem classes instead of the C functions for interacting with the filesystem. However I am getting a strange error when I start my app: When iterating through a directory I suddenly get the message: Aborted. void FileBrowser::rebuild_file_list() { namespace boostfs = boost::filesystem; boostfs::path cur_path( m_cur_dir ); FileContainer tail; // m_files will first only contain directories, // while tail will contain only files m_files.clear(); try { boostfs::directory_iterator end; for( boostfs::directory_iterator dir( cur_path ); dir != end; ++dir ) { std::cout << (*dir).string() << std::endl; if( boostfs::is_directory( *dir ) ) m_files.push_back( *dir ); else tail.push_back( *dir ); } } catch( std::runtime_error & e ) { std::cerr << e.what() << std::endl; } m_files.sort( SortedByName() ); tail.sort( SortedByName() ); drx::list_concat( m_files, tail ); } OUTPUT: [...] /home/mkay/.acrobat /home/mkay/.synce /home/mkay/.gimp-2.0 /home/mkay/.fonts /home/mkay/.designerrctb2 /home/mkay/.eclipse /home/mkay/.gftp /home/mkay/.ntrc_2 /home/mkay/.DCOPserver_anthrax__0 /home/mkay/.DCOPserver_anthrax_:0 /home/mkay/.kpackage /home/mkay/.fonts.conf /home/mkay/.xscreensaver /home/mkay/xdefaults_old /home/mkay/.reslisarc /home/mkay/.aMule /home/mkay/.gtkrc Aborted At this point the application exits. Any idea what is causing this? Thanks in advance, Matthias

5 6

enabling boost::threads for HP-UX
by Oliver Kowalke 31 Jan '05

31 Jan '05

Hi, I want to use boost on HP-UX together with gcc-3.3.2. As I figured out that thread-support is disabled (BOOST_DISABLE_THREADS is defined in file boost/config/platform/hpux.hpp). Up gcc-3.3 posix-threads are supported on HP-UX-plattform (http://gcc.gnu.org/install/specific.html#hppa*-hp-hpux11) Is it then save to remove #define BOOST_DISABLE_THREADS in boost/config/platform/hpux.hpp? with best regards, Oliver -- "Der Spezialist ist ein Barbar, dessen Unwissenheit nicht allumfassend ist." Master's Voice, S.LEM

3 2

Setting the path to use Boost
by Grek 31 Jan '05

31 Jan '05

Hi fellow Boost users! I am new to the Boost Graph Library (BGL) and I have a query about setting the path to access the library. My platform is Cygwin. I want to use the g++ command and incorporate the BGL in it. How do I go about it? Let's say that I want to use the dijkstra's algorithm. I set the path as follows: boost_1_32_0/libs/graph/example Then I typed the following. g++ -g dijkstra-example.cpp But it displays error messages and I do not know how to proceed. It would be of great help if anyone could tell me how one has to set the path to use the dijkstra's algorithm in a program. Thanks for taking the time to read through this! Cheers Grek --------------------------------- Do you Yahoo!? Yahoo! Search presents - Jib Jab's 'Second Term'

2 1

atlanta statics...
by Jeffrey Holle 31 Jan '05

31 Jan '05

http://houseandhome.msn.com/pickaplace/comparecities.aspx?FromState=WA&From… Hope this link works for you. It takes 5 min. to load a page from website for me. Microsoft's MSN uses windows technology now I guess... The big thing that stands out for me is crime. Seattle is above the national average by about 2x, Atlanta appears to be between 7 and 8 times! I'll have to consider such a move with care....

1 1

Thread stack size
by Thorsten Froehlich 30 Jan '05

30 Jan '05

Hi, Googling I found a thread "Boost.Threads. Anything happening?" (in July 2004) in comp.lang.c++.moderated that suggests there should be a development branch of the thread code that already supports this feature. Unfortunately I cannot find the right branch for it in the boost CVS (using the web CVS viewer). The thread_dev and thread_development branches I found do not appear to be the correct ones as they have not been changed for a very long time and the above mentioned thread suggests it would be a rather recently added feature. While I could add this feature myself for the platforms that I need, I would prefer to avoid duplicating work already done. Could someone point me where to find the branch referred to in the above mentioned comp.lang.c++.moderated thread? Regards, Thorsten Froehlich

2 2

Bug in lexical_cast<> with doubles
by Leon Raj 29 Jan '05

29 Jan '05

I think I've found a bug in the boost::lexical_cast<> library (v1.31.0) on WinXP SP1, MSVC 6.0 (sp5) and MSVC.NET 2003. --- Start code snippet --- #include <boost/lexical_cast.hpp> #include <iostream> int main( int argc, char* argv[] ) { double dMax = = std::numeric_limits< double >::max(); // On a Win32 x86 system, dMax is now 1.7976931348623157e+308 // This is successful and strMax is "1.797693134862316e+308" std::string strMax = boost::lexical_cast< std::string >( dMax ); try { double newDMax = boost::lexical_cast< double >( strMax ); std::cout << "Successfuly" << std::endl; } catch ( boost::bad_lexical_cast& ) { std::cout << "Failed to cast" << std::endl; } // On a Win32 x86 system, this always fails, // because (I think) strMax overflows a double, // because 1.7976931348623157e+308 is *rounded UP* // to 1.797693134862316e+308, which cannot be // represented by a double } --- End code snippet --- ----------------------------------------------------- Leon Raj Senior Engineer Invetech Pty. Ltd. Phone: +61 3 9211 7000 (Switchboard) +61 3 9211 7938 (DDI) leon.raj(a)invetech.com.au IMPORTANT - This e-mail and any attachments may be confidential. Any retransmissions, dissemination or other use of these materials by persons or entities other than the intended recipient is prohibited. If received in error, please contact us and delete all copies. Before opening or using attachments, check them for viruses and defects. Our liability is limited to resupplying any affected attachments. [Any representations or opinions expressed in this e-mail are those of the individual sender, and not necessarily those of Vision Systems Limited].

2 1