text: //===----------------------------------------------------------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is dual licensed under the MIT and the University of Illinois Open
  // Source Licenses. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  
  // <ostream>
  
  // template <class charT, class traits = char_traits<charT> >
  //   class basic_ostream;
  
  // basic_ostream<charT,traits>& operator<<
  //           (basic_ostream<charT,traits>& (*pf)(basic_ostream<charT,traits>&))
  
  #include <ostream>
  #include <cassert>
  
  template <class CharT>
  class testbuf
      : public std::basic_streambuf<CharT>
  {
      typedef std::basic_streambuf<CharT> base;
      std::basic_string<CharT> str_;
  public:
      testbuf()
      {
      }
  
      std::basic_string<CharT> str() const
          {return std::basic_string<CharT>(base::pbase(), base::pptr());}
  
  protected:
  
      virtual typename base::int_type
          overflow(typename base::int_type ch = base::traits_type::eof())
          {
              if (ch != base::traits_type::eof())
              {
                  int n = static_cast<int>(str_.size());
                  str_.push_back(static_cast<CharT>(ch));
                  str_.resize(str_.capacity());
                  base::setp(const_cast<CharT*>(str_.data()),
                             const_cast<CharT*>(str_.data() + str_.size()));
                  base::pbump(n+1);
              }
              return ch;
          }
  };
  
  template <class CharT>
  std::basic_ostream<CharT>&
  f(std::basic_ostream<CharT>& os)
  {
      os << "testing...";
      return os;
  }
  
  int main()
  {
      {
          testbuf<char> sb;
          std::ostream os(&sb);
          os << f;
          assert(sb.str() == "testing...");
      }
  }
  