How do I read from ISO-8859-1 stream while converting to UTF-8 in C++?

I am trying to read from a ISO-8859-1 file and convert to UTF-8 before parsing it. I looked for some examples using Boost locale (example below), but couldn't make it work.

What is the recommended way for handling this case?

DefFile parse(std::istream &input);

int main(int argc, char *argv[]) {
  std::fstream file;

  boost::locale::generator gen;
  gen.categories(boost::locale::codepage_facet | boost::locale::convert_facet);
  file.imbue(gen.generate("pt_BR.ISO-8859-1"));
  file.open("RD2008.DEF", std::fstream::in);

  auto df = parse(file);
  // ... do some work
}