Include the iostreams standard header <ios> to define several types and functions basic to the operation of iostreams. (This header is typically included for you by another of the iostreams headers. You seldom have occasion to include it directly.)
A large group of functions are manipulators. A manipulator declared in <ios> alters the values stored in its argument object of class ios_base. Other manipulators perform actions on streams controlled by objects of a type derived from this class, such as a specialization of one of the template classes basic_istream or basic_ostream. For example, noskipws(str) clears the format flag ios_base::skipws in the object str, which might be of one of these types.
You can also call a manipulator by inserting it into an output stream or extracting it from an input stream, thanks to some special machinery supplied in the classes derived from ios_base. For example:
istr >> noskipws;calls noskipws(istr).