[RFC] libstdc++/7811 vs libstdc++/7222

[Paolo Carlini]

Hi all,

I'm currently investigating this regression from 3.1.1. This is the 
testcase:

#include <locale>
#include <iostream>

int main(){
  using namespace std;
  locale loc("");
  cout << loc.name() << endl;
}

What happens with 3.2 and current mainline is that the environment is 
not taken into account and loc is *always* "C".
The regression was introduced with the checkin for libstdc++/7222 (by 
the way, to date I still cannot reproduce it the problem reported therein):

===================================================================
RCS file: /cvs/gcc/gcc/libstdc++-v3/src/locale.cc,v
retrieving revision 1.60
retrieving revision 1.61
diff -u -r1.60 -r1.61
--- gcc/libstdc++-v3/src/locale.cc	2002/04/18 23:47:48	1.60
+++ gcc/libstdc++-v3/src/locale.cc	2002/07/25 06:42:00	1.61
@@ -202,7 +202,7 @@
 	if (strcmp(__s, "C") == 0 || strcmp(__s, "POSIX") == 0)
 	  (_M_impl = _S_classic)->_M_add_reference();
 	else if (strcmp(__s, "") == 0)
-	  _M_impl = new _Impl(setlocale(LC_ALL, __s), 1);
+	  _M_impl = new _Impl(setlocale(LC_ALL, NULL), 1);
 	else
 	  _M_impl = new _Impl(__s, 1);
       }

Now, NULL cannot be correct since by using it the name of the current 
locale is returned which, however, is always "C" in the testcase, 
irrespective of the environment variables. Neither __s can be correct 
since it *sets* the current locale.

I believe that a possible not-MT-aware solution would be the usual pattern

      {
        char* __old = strdup(setlocale(LC_ALL, NULL));
        _M_impl = new _Impl(setlocale(LC_ALL, __s), 1);
        setlocale(LC_ALL, __old);
        free(__old);
      }

Useful to extract the name of the locale set in the environment without 
actually changing it for the running program.

However, I'm not sure about the corresponding MT-aware glibc2.3 solution 
using __uselocale.

Suggestions?

Thanks,
Paolo.