[Bug libgcc/69944] New: ctype::widen issue, use self-define do_widen, get unexpected result.

[derrick at ca dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69944

            Bug ID: 69944
           Summary: ctype::widen issue, use self-define do_widen, get
                    unexpected result.
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgcc
          Assignee: unassigned at gcc dot gnu.org
          Reporter: derrick at ca dot ibm.com
  Target Milestone: ---

I compile the following code under gcc5.2.
$g++ -std=c++11 test.cpp -o test

#include <locale>
#include <codecvt>
#include <stdio.h>
typedef char Mychar;

#include <cctype>
int cnt_;
struct Mycty_ : public std::ctype<Mychar> {
protected:
        Mychar do_widen(char c) const
                {++cnt_;
                return (std::tolower(c)); }
        const char *do_widen(const char *first1,
                const char *last1,
                Mychar *first2) const
               {++cnt_;
               *first2 = do_tolower(*first1);
                return (last1); }
        };

int main(int argc, char *argv[])
{

         Mycty_ fac;
         cnt_ = 0;
         if (fac.widen('A')=='a')
             printf ("111\n");
         if(fac.widen('0')=='0')
             printf("222\n");

         return 0;
}

I expected it should print 111 and 222. But only 111 is print.
If comment "if (fac.widen('A')=='a')", then 222 can be print.

I suspect if the lib has issue.