Given e, produces a suitable value that is not equivalent to eof.
eof
This function is typically used when a value other than eof needs to be returned, such as in implementations of std::basic_streambuf::overflow().
See CharTraits for the general requirements on character traits for X::not_eof.
X::not_eof
e if e and eof value are not equivalent, or some other non-eof value otherwise.
Constant.
