"Jonathan Turkanis" <technews@kangaroologic.com> wrote in message news:crlh51$6kh$1@sea.gmane.org... | Thorsten Ottosen wrote: | > "Jonathan Turkanis" <technews@kangaroologic.com> wrote: | | >>> 4. Thorsten asks why the widening and narrowing functions shouldn't | >>> be non-member functions. One answer is that code conversion can be | >>> (slightly) more efficient if a large buffer is used. Making the core | >>> conversion functions member functions allows buffers to be used for | >>> several string conversions. | | >> I think the added flexibility of the overloads taking iterators is | >> more significant than the ability to buffer. | > | > I can't really figure out how this buffering should work. Buffering | > of what? | | Look at the interface of std::codecvt, e.g. at the member function in. This | function takes a Byte array as input and write wide characters to a second Byte | array. Since in() is a virtual function, it's slightly faster to call it once or | twice per string than to call it once for each character in a string. Similar | remarks hold for out. To make this work, you need | | (i) the input to be presented as a character array (std::string or const char* | is fine, but a pair of forward iterators isn't) sorry I should have looked. that said, we can of course also consider changes to codecvt interface; we are allowed to do that. | > Jonathan: | >> template<typename WideStr> | >> basic_string<typename Codecvt::extern_type> | >> narrow(const WideStr& str) | >> { | >> string_converter<> cvt; | >> return cvt::narrow(str); | >> } | > | > The could be specified as | > | > template< class NarrowString, class ReadableWideForwardRange, class | > Codecvt > NarrowString narrow( const ReadableWideForwardRange& r, | > const Codecvt& cc ); ... | | First, as much as I love Boost.Range and would like to see it standardized, I | don't think the code conversion proposal should use it. I just assumed that a Range based version was not that far from the iterator version you wanted | The second problem is that it's awkard to specify the codecvt instance when you | just want a codecvt to be grabbed from the globale locae: | | std::locale loc = locale::global(); | const std::codecvt<wchar_t, char, std::mbstate_t>& cvt = | std::use_facet< std::codecvt<wchar_t, char, std::mbstate_t> >(loc); | // etc. | std::string s = narrow(ws, cvt); | | Most people will want to be able to write | | std::string s = narrow(ws); template< class NarrowString, class Range, class Codecvt > inline NarrowString narrow( const Range& r, const Codecvt& = std::use_facet< std::codecvt< typename range_value<Range>::type, typename range_value<NarrowString>::type, std::mbstate_t>
( locale::global() ) );
| Perhaps a good solution would be to have overloads, in addition to the ones I | showed, with a signature including a codecvt instance, as in your example. yes. -Thorsten