[Bug libstdc++/64315] New: num_put misbehaves if the C library doesn't support floats

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64315

            Bug ID: 64315
           Summary: num_put misbehaves if the C library doesn't support
                    floats
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ville.voutilainen at gmail dot com

In num_put::_M_insert_float, __convert_from_v can fail, leading into a __widen
being called with a negative size. This may happen with a C library that has a
sprintf that refuses to support floats and returns -1 when a float is used with
it.