[Bug libstdc++/81138] New: std::money_put facet does not write '0' before decimal point

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81138

            Bug ID: 81138
           Summary: std::money_put facet does not write '0' before decimal
                    point
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
  cout.imbue(locale("en_US"));
  cout << showbase;
  cout << put_money(99);
  cout << '\n';
}

This prints $.99 rather than $0.99

This happens for all locales with with non-zero moneypunct<>::frac_digits().

The following untested patch fixes it, but I don't know if it breaks other
locales:


--- a/libstdc++-v3/include/bits/locale_facets_nonio.tcc
+++ b/libstdc++-v3/include/bits/locale_facets_nonio.tcc
@@ -471,6 +471,8 @@ _GLIBCXX_BEGIN_NAMESPACE_LDBL_OR_CXX11
                else
                  __value.assign(__beg, __paddec);
              }
+           else
+             __value.assign(1, __lit[money_base::_S_zero]);

            // Deal with decimal point, decimal digits.
            if (__lc->_M_frac_digits > 0)