How to load wxXmlDocument from std::istream?

Question

I would like to load a wxXmlDocument from a std::istream but unfortunately, there's no Load(std::istream&) member function, even if wxWidget is compiled using standard input/output streams.

For what it's worth, I'm using wxWidgets 3.1.0 on macOS.

Answer 1

I don't know if there are alternatives but, since wxXmlDocument provides a Load(wxInputStream&), a solution can be to define an adapter like this one:

class myStdInputStreamAdapter : public wxInputStream {
public:
  myStdInputStreamAdapter(std::istream &s): stream{s} {}

protected:
  std::istream &stream;

  virtual size_t OnSysRead(void *buffer, size_t bufsize) {
    std::streamsize size = 0;

    stream.peek();

    if (stream.fail() || stream.bad()) {
      m_lasterror = wxSTREAM_READ_ERROR;
    } else if (stream.eof()) {
      m_lasterror = wxSTREAM_EOF;
    } else {
      size = stream.readsome(static_cast<std::istream::char_type *>(buffer),
                             bufsize);
    }

    return size;
  }
};

And then use it to load the xml:

void f(std::istream &istream) {
    wxXmlDocument xml;

    myStdInputStreamAdapter inputStreamAdapter(istream);

    xml.Load(inputStreamAdapter);
}