15.4 State of Streams
Streams maintain a state. The state identifies whether I/O was successful and, if not, the reason for the failure.
15.4.1 Constants for the State of Streams
For the general state of streams, several constants of type iostate are defined to be used as flags (Table 15.3). The type iostate is a member of the class ios_base. The exact type of the constants is an implementation detail; in other words, it is not defined whether iostate is an enumeration, a type definition for an integral type, or an instantiation of the class bitset