std::char_traits<CharT>::not_eof

static int_type not_eof( int_type e );		(until C++11)
static constexpr int_type not_eof( int_type e ) noexcept;		(since C++11)

Checks whether e is not equivalent to eof value.

Formally.

if X::eq_int_type(e, X::eof()) is false, returns e
otherwise, returns a value f such that X::eq_int_type(f, X::eof()) is false

value to analyze

e if e and eof value are not equivalent, returns some other non-eof value otherwise.

Constant.