std::getline and wfstream

std::wfstream f;
f.open( L"file.txt", std::ios::in); //error: no matching function for call to 'std::basic_fstream<wchar_t>::open(const wchar_t*, std::ios_base::openmode&)'

My compiler is giving me an error when reading this line, can anyone spot what I am dong wrong?

Thanks in advance.