//===----------------------------------------------------------------------===//
//
//                     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 __c = base::traits_type::eof())
        {
            if (__c != base::traits_type::eof())
            {
                int n = str_.size();
                str_.push_back(__c);
                str_.resize(str_.capacity());
                base::setp(const_cast<CharT*>(str_.data()),
                           const_cast<CharT*>(str_.data() + str_.size()));
                base::pbump(n+1);
            }
            return __c;
        }
};

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...");
    }
}