iostream changes locale to format a number

[Paolo Carlini]

Paolo Carlini wrote:

> Are you willing to contribute a patch against the current mainline 
> libstdc++-v3 sources for public discussion (that setlocale ... 
> setlocale pattern is present in quite a few different places) ?

Let me point out, however, that, assuming your analysis is correct (I 
believe is) the solution cannot be as simple as you seems to assume: the 
string returned by the first setlocale must be saved! See the following 
excerpts from glibc2.2.5 docs:

...

     To be sure you can use the returned string encoding the currently
     selected locale at a later time, you must make a copy of the
     string.  It is not guaranteed that the returned pointer remains
     valid over time.

...

   Here is an example showing how you might use `setlocale' to
temporarily switch to a new locale.

     #include <stddef.h>
     #include <locale.h>
     #include <stdlib.h>
     #include <string.h>
    
     void
     with_other_locale (char *new_locale,
                        void (*subroutine) (int),
                        int argument)
     {
       char *old_locale, *saved_locale;
    
       /* Get the name of the current locale.  */
       old_locale = setlocale (LC_ALL, NULL);
    
       /* Copy the name so it won't be clobbered by `setlocale'. */
       saved_locale = strdup (old_locale);
       if (saved_locale == NULL)
         fatal ("Out of memory");
    
       /* Now change the locale and do some stuff with it. */
       setlocale (LC_ALL, new_locale);
       (*subroutine) (argument);
    
       /* Restore the original locale. */
       setlocale (LC_ALL, saved_locale);
       free (saved_locale);
     }

...

Ciao,
Paolo.