- Boost-users - lists.boost.org

[mpl] calling a function depending on type or instance as argument
by martin f krafft 14 May '05

14 May '05

Dear all, another MPL question (at least I think it's the domain of MPL): I have a templated class Foo and need to make an instance based on the type of an instance at various points in the code, which is simple: template <typename T> Foo<T> get_foo_for(T const&) { return Foo<T>; } //... get_foo_for(myObj).doSomethingWithFoo(); At times, I don't have an instance of an object, just the typename. I do not want to assume that all types are default constructible (which could be expensive anyway), so I have to do: Foo<T>().doSomethingWithFoo(); I am hiding these two behind two separate macros which I would like to unify. The situation is actually more complex but boils down to the following question: How can I create a macro (#define) such that its definition does different things when passed an instance or a typename. Something like: if is_type(Arg) do_this(); else do_that(); Again, I cannot figure this out from the MPL docs. There is enable_if and if_c, but both seem to deal with the definition of symbols and/or types, not with the selection of functions to call. I appreciate any hint. -- martin; (greetings from the heart of the sun.) \____ echo mailto: !#^."<*>"|tr "<*> mailto:" net@madduck invalid/expired pgp subkeys? use subkeys.pgp.net as keyserver! spamtraps: madduck.bogus(a)madduck.net "arguments are extremely vulgar, for everyone in good society holds exactly the same opinion." -- oscar wilde

1 0

[mpl] calling a function depending on availability of *this
by martin f krafft 14 May '05

14 May '05

Dear all, I am trying to create an assertion macro which can be used inside and outside of class member functions. When inside a class, I want it to be able to use information from *this, which obviously does not exist outside of a class member function. Right now, I have two different macros and I would like to unify the API. The situation is actually more complex but boils down to the following question: How can I create a macro (#define) such that its definition does different things when inside a class member function than outside. Something like: if exists(*this) assertion(a, *this); else assertion(a); such that this is resolved to either of the assertion() overloads at compile time. I guess this is the domain of MPL, but my head just doesn't work in MPL-terms (yet). I would appreciate if someone gave me a solution to this case and promise to try to work my way into MPL more with it. -- martin; (greetings from the heart of the sun.) \____ echo mailto: !#^."<*>"|tr "<*> mailto:" net@madduck invalid/expired pgp subkeys? use subkeys.pgp.net as keyserver! spamtraps: madduck.bogus(a)madduck.net "arguments are extremely vulgar, for everyone in good society holds exactly the same opinion." -- oscar wilde

1 0

enable_if< is_convertible > w/ explicit constructor trouble
by me22 14 May '05

14 May '05

After reading a recent Joel on Software article ( http://www.joelonsoftware.com/items/2003/10/13.html ) and the discussion it generated, I decided to try to write some sort of general strong typedef. I've started out by creating a specific class similar to what would be generated by a `typedef strong_typedef<tag,wrapped_type> name;`, and am trying to use enable_if and is_convertible to allow explicit construction from any type that can be converted to the wrapped type. Unfortunately, I keep getting errors such as the following: main.cpp:36: error: no matching function for call to `position::position(int)' main.cpp:7: error: candidates are: position::position(const position&) main.cpp:14: error: position::position() Compiler version: g++ (GCC) 3.3.5-20050130 (Gentoo Linux 3.3.5.20050130-r1, ssp-3.3.5.20050130-1, pie-8.7.7.1) Here's the cut down code. I'd greatly appreciate it if someone could point me towards what I'm doing wrong. Hopefully I'm just missing something elementary. ( I'm quite new to these boost features. ) On a side note, has anyone come up with a good method of wrapping these rather long SFINAE calls? Thanks, - Scott McMurray // begin code // #include <boost/type_traits.hpp> #include <boost/utility/enable_if.hpp> class position { public: typedef position my_type; typedef unsigned wrapped_type; private: wrapped_type m_data; public: position() {} // This works fine explicit position(boost::enable_if< boost::is_convertible<int, wrapped_type>, int>::type f) : m_data( f ) {} /* // But if I try this, I get the errors template <typename fT> explicit position(typename boost::enable_if< boost::is_convertible<fT, wrapped_type>, fT>::type f) : m_data( f ) {} */ }; int main(int argc, char* argv[]) { position x = position(5); } // end code //

3 4

numeric_cast
by Marcin Kalici�ski 13 May '05

13 May '05

How do I make boost::numeric_cast work with a custom class? What templates do I need to specialize? converter? numeric_cast itself? The documentation is not quite clear about that, I have read it and studied the source code for some time, but found no clue. I think there should be a section about that in the docs. cheers, M.

2 1

Serialization of cross-pointing objects
by Henrik Jacobsson 13 May '05

13 May '05

Hi! I want to serialize objects that link to each other through pointers, like a linked list, but in this case a more complex graph with several different classes and proxies (a graph which can contain loops and and null-pointers). But I get the "pointer conflict" exception since the serialization discovers that an object have been serialized once before through its pointer. The contents should be serialized/deserialized only once, and then the pointers should just be kept consistent. An alternative is of course to replace all the pointers with indeces which are memory-independent. But that's a messy affair. In the copy constructor I solved something similar through a map<Type*,Type*> which mapped from the old pointers to the newly allocated ones, so that they could be properly replaced. Is something like this hidden somewhere in the lib? Any suggestions? Best regards, Henrik Jacobsson

3 15

RE: [Boost-users] what gets posted
by Marcin Tustin 13 May '05

13 May '05

I believe so. I never see messages I post, or at least I didn't until I went over to daily digests. > -----Original Message----- > From: Andreas Fabri [mailto:Andreas.Fabri@geometryfactory.com] > Sent: 13 May 2005 10:44 > To: boost-users(a)lists.boost.org > Subject: [Boost-users] what gets posted > > > Hello, > > I recently posted a mail to the list, and got this mail from > boost-users-bounces(a)lists.boost.org > > ___________________________________________________________ > > Your message entitled > > BGL question: edge order > > was successfully received by the Boost-users mailing list. > > List info page: > http://lists.boost.org/mailman/listinfo.cgi/boost-users > Your preferences: > http://lists.boost.org/mailman/options.cgi/boost-users/andreas .fabri%40geometryfactory.com > > > ___________________________________________________________ > > > I find it in the archive, but I didn't receive it as mail. > Is this the policy of the list, that is I have to cc: it to myself? > > andreas > >

1 0

program_options and ->notify(&your_function)
by Susan Flynn 13 May '05

13 May '05

Hi, I'm new to boost (and c++) and I've just started using program_options. Great concept and code, it has saved me a lot of time/effort, thanks. I am having a problem with the ->notify(&your_function) in add_options. I get a compile error (g++ on redhat): "invalid use of void expression". If I comment out the ->notify(&func) part, the code compiles. This is the code: void Report::PrintName(const string name) { cout << " the log name is " << name << "\n"; } void Report::InitCmdOpts(void) { try { p_opts = new po::options_description("Reporting"); p_opts->add_options() ("log", po::value< string >() ->default_value("sys.log") ->notify( &Report::PrintName)) ; } ...catch code... } Any help/ideas appreciated. I'm hoping it's something simple and my lack of c++ knowledge is showing. I've already simplified the code and tried several modifications, but the compile error persists. thanks, susan. __________________________________ Do you Yahoo!? Yahoo! Mail - You care about security. So do we. http://promotions.yahoo.com/new_mail

2 4

what gets posted
by Andreas Fabri 13 May '05

13 May '05

Hello, I recently posted a mail to the list, and got this mail from boost-users-bounces(a)lists.boost.org ___________________________________________________________ Your message entitled BGL question: edge order was successfully received by the Boost-users mailing list. List info page: http://lists.boost.org/mailman/listinfo.cgi/boost-users Your preferences: http://lists.boost.org/mailman/options.cgi/boost-users/andreas.fabri%40geom… ___________________________________________________________ I find it in the archive, but I didn't receive it as mail. Is this the policy of the list, that is I have to cc: it to myself? andreas

2 1

need help about wide character stream
by Tom Tan (SH/RDC) 13 May '05

13 May '05

hi,all i have 3 questions. 1. When i was trying wide character streams like wifstream ,wofstream , wcout etc. , i failed every time. My default locale is en_US.UTF-8. I created a test file , wrote a line Chinese "??" in that file. Then I try to use wifstream to read that file, after reading, i print it to stdout and write to another file. As a result , i got nothing. Assuming "input.txt" is the input file which contains Chinese character. BTW , input.txt is encoded with UTF-8. locale.global("en_US.UTF-8"); wifstream win("input.txt"); wcout<<win.rdbuf()<<endl; wofstream wout("output.txt"); wout<<win.rdbuf()<<endl; wout.close(); I got ouput: $ <nothing> $ wc -c outpu.txt $ 0 output.txt I am deeply puzzled, How does wide character stream works? 2. Can anybody explain why IBM ICU (International Component for Unicode) exists? What 's it for by comparing with stdc++ wide character mechanism? If it is necessary , is there any consideration to invent a similar package in BOOST? 3. Since my post looks more like a stdc++ question , anybody can tell me how i can join a stdc++ mail list? Thanks in advance. /Tom

1 0

[iostreams] calling sink member function
by Daniel Schlyder 13 May '05

13 May '05

Hi, The following used to compile with MinGW GCC 3.4.2: <code> #include <boost/iostreams/concepts.hpp> #include <boost/iostreams/stream_facade.hpp> #include <iostream> class my_sink : public boost::iostreams::sink { public: std::streamsize write(char const *, std::streamsize size) { return size; } void foo() { std::cout << "foo() called" << std::endl; } }; int main() { boost::iostreams::stream_facade<my_sink> out; out->foo(); return 0; } </code> Now I get the following error: E:/libs/boost/boost/iostreams/stream_facade.hpp: In member function `my_sink * boost::iostreams::stream_facade<my_sink, char_traits<char> > ::operator->()': boost_iostreams_issues.cpp:36: instantiated from here E:/libs/boost/boost/iostreams/stream_facade.hpp:119: error: no match for 'operator *' in '*( ( ( boost::base_from_member< boost::iostreams::streambuf_facade< my_sink, char_traits<char>, boost::iostreams::output >, 0 > * )( (boost::iostreams::stream_facade<my_sink, char_traits<char> > * )this ) ) + 4u )->boost::base_from_member< boost::iostreams::streambuf_facade< my_sink, char_traits<char>, boost::iostreams::output >, 0 >::member' It compiles if I remove the call to foo(). What must I do to make it work again? Thanks, -- Daniel Schlyder http://bitblaze.com/

2 2