Question

Is there a (clean) way to manipulate some text from std::cin before inserting it into a std::string, so that the following would work:

cin >> setw(80) >> Uppercase >> mystring;

where mystring is std::string (I don’t want to use any wrappers for strings).
Uppercase is a manipulator. I think it needs to act on the Chars in the buffer directly (no matter what is considered uppercase rather than lowercase now). Such a manipulator seems difficult to implement in a clean way, as user-defined manipulators, as far as I know, are used to just change or mix some pre-determined format flags easily.

Answer 1

(Non-extended) manipulators usually only set flags and data which the extractors afterwards read and react to. (That is what xalloc, iword, and pword are for.) What you could, obviously, do, is to write something analogous to std::get_money:

struct uppercasify {
  uppercasify(std::string &s) : ref(s) {}
  uppercasify(const uppercasify &other) : ref(other.ref) {}
  std::string &ref;
}
std::istream &operator>>(std::istream &is, uppercasify uc) { // or &&uc in C++11
  is >> uc.ref;
  boost::to_upper(uc.ref);
  return is;
}

cin >> setw(80) >> uppercasify(mystring);

Alternatively, cin >> uppercase could return not a reference to cin, but an instantiation of some (template) wrapper class uppercase_istream, with the corresponding overload for operator>>. I don’t think having a manipulator modify the underlying stream buffer’s contents is a good idea.

If you’re desperate enough, I guess you could also imbue a hand-crafted locale resulting in uppercasing strings. I don’t think I’d let anything like that go through a code review, though – it’s simply just waiting to surprise and bite the next person working on the code.