[Bug libstdc++/57273] stringstream str initialization fails

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57273

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Which also explains that you can make the inserted characters append to the
buffer using std::ios::ate

e.g.
  std::stringstream tmpLabel(std::ios::ate|std::ios::out);

or using an ostringstream
  std::ostringstream tmpLabel(std::ios::out);