The State of the Stream

Flags represent the state of the stream stream. The methods for dealing with these flags need the header <iostream>.

Flag	Query of the flag	Description
std::ios::goodbit	stream.good()	No bit set
std::ios::eofbit	stream.eof()	end-of-file bit set
std::ios::failbit	stream.fail()	Error
std::ios::badbit	stream.bad()	Undefined behaviour

State of a stream

Here are examples for conditions causing the different states of a stream:

std::ios::eofbit:

• Reading beyond the last valid character.

std::ios::failbit:

• False formatted reading.
• Reading beyond the last valid character.
• Opening of a file went wrong.

std::ios::badbit:

• The size of the stream buffer cannot be adjusted.
• The code conversion of the stream buffer went wrong.
• A part of the stream threw an exception.

stream.fail():

• returns whether std::ios::failbit or std::ios::badbit is set.

The state of a stream can be read and set in the following ways:

stream.clear():
Initializes the flags and sets the stream in the goodbit state.

stream.clear(sta):
Initializes the flags and sets the stream sta state.

stream.rdstate():
Returns the current state.

stream.setstate(fla):
Sets the additional flag fla.

Operations on a stream only work if the stream is in the goodbit state. If the stream is in the badbit state, when cannot set it to the goodbit state.