Annex D (normative) Compatibility features [depr]

D.10 char* streams [depr.str.strstreams]

D.10.1 Header <strstream> synopsis [depr.strstream.syn]

The header <strstream> defines types that associate stream buffers with character array objects and assist reading and writing such objects.
namespace std {
  class strstreambuf;
  class istrstream;
  class ostrstream;
  class strstream;
}