The first form (1) returns the current value of the field width.
The second form (2) also sets a new field width for the stream.
The field width determines the minimum number of characters to be written in some output representations. If the standard width of the representation is shorter than the field width, the representation is padded with fill characters at a point determined by the format flag adjustfield (one of left, right or internal).
The fill character can be retrieved or changed by calling the member function fill.
The format flag adjustfield can be modified by calling the member functions flags or setf, by inserting one of the following manipulators: left, right and internal, or by inserting the parameterized manipulator setiosflags.
The field width can also be modified using the parameterized manipulator setw.
New value for the stream's field width. streamsize in signed integral type.