Class input_stream_adapter

dependencies/json/json.hpp:4858–4906

! Input adapter for a (caching) istream. Ignores a UFT Byte Order Mark at beginning of input. Does not support changing the underlying std::streambuf in mid-input. Maintains underlying std::istream and std::streambuf to support subsequent use of standard std::istream operations to process any input characters following those used in parsing the JSON input. Clears the std::istream flags; any input

subsequent call for input from the std::istream.
*/
class input_stream_adapter
{
  public:
    using char_type = char;

    ~input_stream_adapter()
    {
        // clear stream flags; we use underlying streambuf I/O, do not
        // maintain ifstream flags, except eof
        if (is != nullptr)
        {
            is->clear(is->rdstate() & std::ios::eofbit);
        }
    }

    explicit input_stream_adapter(std::istream& i)
        : is(&i), sb(i.rdbuf())
    {}

    // delete because of pointer members
    input_stream_adapter(const input_stream_adapter&) = delete;
    input_stream_adapter& operator=(input_stream_adapter&) = delete;
    input_stream_adapter& operator=(input_stream_adapter&& rhs) = delete;

    input_stream_adapter(input_stream_adapter&& rhs) noexcept : is(rhs.is), sb(rhs.sb)
    {
        rhs.is = nullptr;
        rhs.sb = nullptr;
    }

    // std::istream/std::streambuf use std::char_traits<char>::to_int_type, to
    // ensure that std::char_traits<char>::eof() and the character 0xFF do not
    // end up as the same value, eg. 0xFFFFFFFF.
    std::char_traits<char>::int_type get_character()
    {
        auto res = sb->sbumpc();
        // set eof manually, as we don't use the istream interface.
        if (JSON_HEDLEY_UNLIKELY(res == EOF))
        {
            is->clear(is->rdstate() | std::ios::eofbit);
        }
        return res;
    }

  private:
    /// the associated input stream
    std::istream* is = nullptr;
    std::streambuf* sb = nullptr;
};

// General-purpose iterator-based adapter. It might not be as fast as
// theoretically possible for some containers, but it is extremely versatile.