Effects: Behaves as an unformatted input function (
[istream.unformatted]), except that it does not count the number of characters extracted and
does not affect the value returned by subsequent calls to
is.gcount(). After
constructing a
sentry object extracts characters as long as the next available
character
c is whitespace or until there are no more characters in the sequence
. Whitespace characters are distinguished with the same criterion as used by
sentry::sentry (
[istream.sentry])
. If
ws
stops extracting characters because there are no more available it sets
eofbit,
but not
failbit.