[iostate.flags]

explicit operator bool() const;

Returns: !fail().

bool operator!() const;

Returns: fail().

iostate rdstate() const;

Returns: The error state of the stream buffer.

void clear(iostate state = goodbit);

Effects: If ((state | (rdbuf() ? goodbit : badbit)) & exceptions() == 0, returns.

Otherwise, the function throws an object of class ios_base::failure ([ios.failure]), constructed with implementation-defined argument values.

Postconditions: If rdbuf() != 0 then state == rdstate(); otherwise rdstate() == (state | ios_base::badbit).

void setstate(iostate state);

Effects: Calls clear(rdstate() | state) (which may throw ios_base::failure ([ios.failure])).

bool good() const;

Returns: rdstate() == 0.

bool eof() const;

Returns: true if eofbit is set in rdstate().

bool fail() const;

Returns: true if failbit or badbit is set in rdstate().256

bool bad() const;

Returns: true if badbit is set in rdstate().

iostate exceptions() const;

Returns: A mask that determines what elements set in rdstate() cause exceptions to be thrown.

void exceptions(iostate except);

Effects: Calls clear(rdstate().

Postconditions: except == exceptions().

Checking badbit also for fail() is historical practice.

31 Input/output library [input.output]