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:

1. http://www.cplusplus.com/reference/ios/ios/fail/
   
2. http://www.cplusplus.com/reference/ios/ios/operator_not/
   
3. http://stackoverflow.com/questions/6255339/checking-if-a-file-opened-successfully-with-ifstream
   
4. http://www.cplusplus.com/forum/beginner/6033/
   
5. http://www.cplusplus.com/doc/tutorial/files/