[cfe-dev] [libcxx]handling missing linux implementations

[Larry Evans]

On 02/15/11 12:03, Howard Hinnant wrote:
> On Feb 14, 2011, at 11:26 PM, Larry Evans wrote:
>
>> Mybe a proper implementation could be done using the 'uselocale'
>> described on p. 131 of:
>>
>>  http://people.redhat.com/drepper/tllocale.ps.gz
>>
>> (Thanks to  Marc Glisse for suggesting uselocale here:
>>
>>  http://llvm.org/bugs/show_bug.cgi?id=8992#c11
>>
>> )
>>
>>
>> Uselocale could be used something like in the following code:
>>
>>  #ifdef __linux__
>>    namespace std
>>    {
>>        size_t
>>      wcrtomb_l
>>        ( char* et
>>        , wchar_t it
>>        , mbstate_t* ps
>>        , locale_t locale_new
>>        )
>>        {
>>          locale_t locale_old uselocale(locale_new);
>>          wcrtomb(et,it,st);
>>          uselocale(locale_old);
>>        }
>>    }
>>  #endif
>>
>> The above could be inserted just after the #include's in:
>>
>>
http://llvm.org/viewvc/llvm-project/libcxx/trunk/src/locale.cpp?annotate=121510
>>
>> Some similar could be done for other "missing _l suffixed functions".
>>
>> Anyone have any alternatives to this solution to the missing _l
>> suffixed functions on linus (or really, in glibc)?
>
> I think this is a really promising direction.  What we need to know
> now is:  How available is uselocale on the platforms that this
> audience wants to port libc++ to?  Does just Ubuntu have it?  Other
> linux platforms?  Windows?

What about handling other platforms by inserting:

#ifndef __APPLE__
//Purpose:
//  Provide functions whose name is suffixed with _l
//  and which have locale_t as last argument, but
//  which are missing on ubuntu (and presumably other
//  unix type OS's).
//Method:
//  Use uselocale to temporarlity change the current
//  threads locale to the last argument, then
//  perform the operation with the abbreviated function
//  (i.e. same name except without _l suffix), and then
//  restore the locale to previous value.
//

#if defined(__GLIBC__)
  #if __GLIBC__ > 1 && __GLIBC_MINOR__ > 2
    //From page 141 of http://people.redhat.com/drepper/tllocale.ps.gz:
    //  Starting with glibc 2.3 everyting will be available
    //So, indicate that uselocale is available in glibc:
    #define _LIBCPP_HAS_USELOCALE
  #endif
#endif

  size_t
wcrtomb_l
  ( char* et
  , wchar_t it
  , mbstate_t* ps
  , locale_t locale_new
  )
  {
  #if defined(__LIBCPP_HAS_USELOCALE)
    locale_t locale_old=uselocale(locale_new);
  #endif
    size_t result=wcrtomb(et,it,ps);
  #ifdef defined(__LIBCPP_HAS_USELOCALE)
    uselocale(locale_old);
  #else
    #warning "wcrtomb_l improperly implemented for this config."
  #endif
    return result;
  }

#endif

just after the anonymous namespace open curly braces in locale.cpp
(IOW, just after line 26 of:

http://llvm.org/viewvc/llvm-project/libcxx/trunk/src/locale.cpp?annotate=121510
)?

The #if __GLIB_* test would assure it would work for any platform
using glibc.  For windows, since _LIBCPP_HAS_USELOCALE would be
undefined, the #warning would occur, but the result would be no worse
than the current implementation and the user would be notified of a
possible problem (thanks to Matthieu for this suggestion).

[snip]

-Larry