right way check file open and end

check if a state is ok

while(cin >> word)
// ok: read successful

condition states are constants defined in ios_base as public members
- ios_base::badbit : corrupted.
  - set when the error involves the loss of integrity of the stream, which is likely to persist even if a different operation is attempted on the stream.
  - indicates a system-level failure, such as an unrecoverable read or write error.
  - usually not possible to use a stream once badbit has been set.
- ios_base::failbit : failed.
  - set by an operation when the error is related to the internal logic of the operation itself; further operations on the stream may be possible.
  - is set after a recoverable error, such as reading a character when numeric data was expected.
  - often possible to correct such problems and continue using the stream.
- ios_base::eofbit : hit end-of-file.
- ios_base::goodbit : not in an error state.
  - indicating none of the other bits is set.
Note
- At least one of failbit and badbit is set when an error occured during an input operation.
- Failing to read due to reaching the end-of-file sets both eofbit and failbit.
- fail() is a synonym of ios::operator!
checks
- s.bad() : eofbit is set.
- s.fail() : failbit or badbit is set.
- s.eof() : eof is set.
- s.good() : none of above three states is set.
- s.is_open() :
- s.clear() : reset all condition values in the stream to valid state.
operation on flags
- retrieve : basic_ios::rdstate
- set : basic_ios::setstate
about types:
- std::ios_base::iostate is type for stream error state flags

References: