std::ios_base::iostate

 

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typedef /*implementation defined*/ iostate;
static constexpr iostate goodbit = 0;
static constexpr iostate badbit  = /* implementation defined */ static constexpr iostate failbit = /* implementation defined */ static constexpr iostate eofbit  = /* implementation defined */

Specifies stream state flags. It is a BitmaskType, the following constants are defined:

Constant	Explanation
goodbit	no error
badbit	irrecoverable stream error
failbit	input/output operation failed (formatting or extraction error)
eofbit	associated input sequence has reached end-of-file

The eofbit

The eofbit is set by the following standard library functions:

• The string input function std::getline if it completes by reaching the end of the stream, as opposed to reaching the specified terminating character.
• The numeric input overloads of basic_istream::operator>> if the end of the stream was encountered while reading the next character, on Stage 2 of num_get::get processing. Depending on the parsing state, failbit may or may not be set at the same time: for example, int n; istringstream buf("1"); buf >> n; sets eofbit, but not failbit: the integer 1 was successfully parsed and stored in n. On the other hand, bool b; istringstream buf("tr"); buf >> boolalpha >> b; sets both eofbit and failbit: there was not enough characters to complete the parsing of the boolean true.
• The character extraction overloads of operator>>std::basic_istream, if the end of the stream is reached before the limit (if any) on the number of characters to be extracted.
• The std::get_time I/O manipulator and any of the std::time_get parsing functions: time_get::get, time_get::get_time, time_get::get_date, etc., if the end of the stream is reached before the last character needed to parse the expected date/time value was processed.
• The std::get_money I/O manipulator and money_get::get function, if the end of the stream is reached before the last character needed to parse the expected monetary value was processed.
• The basic_istream::sentry constructor, executed at the beginning of every formatted input function: unless the skipws bit is unset (e.g. by issuing std::noskipws), sentry reads and discards the leading whitespace characters. If the end of the input stream is reached during this operation, both eofbit and failbit are set, and no input takes place.
• The I/O manipulator std::ws, if it reaches the end of the stream while consuming whitespace (but, unlike the formatted input sentry, it does not set failbit in this case).
• The unformatted input functions basic_istream::read, basic_istream::get, basic_istream::peek, basic_istream::readsome, basic_istream::ignore, and basic_istream::getline, when reaching the end of the stream.
• The discard input function basic_istream::ignore, when reaching the end of the stream before reaching the specified delimiter character.
• The immediate input function basic_istream::readsome, if basic_streambuf::in_avail returns -1.

The following functions clear eofbit as a side-effect:

• basic_istream::putback
• basic_istream::unget
• basic_istream::seekg

Note that in nearly all situations, if eofbit is set, the failbit is set as well.

The failbit

The failbit is set by the following standard library functions:

• The basic_istream::sentry constructor, executed at the beginning of every input function, if either eofbit or badbit is already set on the stream, or if the end of stream is encountered while consuming leading whitespace.
• The basic_ostream::sentry constructor, executed at the beginning of every output function, under implementation-defined conditions.
• operator>>(std::basic_string<>) if the function extracts no characters from the input stream.
• operator>>(std::complex<>) if the function fails to extract a valid complex number.
• The character array and single character overloads of operator>> if they fail to extract any characters.
• The streambuf overload of basic_istream::operator>> if the streambuf argument is a null pointer or if no characters were inserted into the streambuf.
• The streambuf overload of basic_ostream::operator<< if the function inserts no characters.
• operator>>(std::bitset<>) if the function extracts no characters from the input stream.
• std::getline if the function extracts no characters or if it manages to extract basic_string::max_size characters from the input stream.
• The numeric, pointer, and boolean input overloads of basic_istream::operator>> (technically, the overloads of num_get::get they call), if the input cannot be parsed as a valid value or if the value parsed does not fit in the destination type.
• The time input manipulator std::get_time (technically, time_get::get it calls), if the input cannot be unambiguously parsed as a time value according to the given format string.
• The currency input manipulator std::get_money (technically, money_get::get it calls), if the input cannot be unambiguously parsed as a monetary value according to the locale rules.
• The extraction operators of all RandomNumberEngines, if bad input is encountered.
• The extraction operators of all RandomNumberDistributions, if bad input is encountered.
• The unformatted input functions basic_istream::get if they fails to extract any characters.
• basic_istream::getline, if it extracts no characters, if it fills in the provided buffer without encountering the delimiter, or if the provided buffer size is less than 1.
• basic_istream::read, if the end-of-file condition occurs on the input stream before all requested characters could be extracted.
• basic_istream::seekg on failure
• basic_ostream::tellp on failure
• The constructors of std::basic_fstream, std::basic_ifstream, and std::basic_ofstream that takes a filename argument, if the file cannot be opened.
• basic_fstream::open, basic_ifstream::open, and basic_ofstream::open if the file cannot be opened.
• basic_fstream::close, basic_ifstream::close, and basic_ofstream::close if the file cannot be closed.

The badbit

The badbit is set by the following standard library functions:

• basic_ostream::put if it fails to insert a character into the output stream, for any reason.
• basic_ostream::write if it fails to insert a character into the output stream, for any reason.
• Formatted output functions operator<<, std::put_money, and std::put_time, if they encounter the end of the output stream before completing output.
• basic_ios::init when called to initialize a stream with a null pointer for rdbuf().
• basic_istream::putback and basic_istream::unget when called on a stream with a null rdbuf().
• basic_ostream::operator<<(basic_streambuf*) when a null pointer is passed as the argument.
• basic_istream::putback and basic_istream::unget if rdbuf()->sputbackc() or rdbuf()->sungetc() return traits::eof().
• basic_istream::sync, basic_ostream::flush, and every output function on a unitbuf output stream, if rdbuf()->pubsync() returns -1.
• Every stream I/O function if an exception is thrown by any member function of the associated stream buffer (e.g. sbumpc(), xsputn(), sgetc(), overflow(), etc).
• ios_base::iword and ios_base::pword on failure (e.g. failure to allocate memory).

See also

The following table shows the value of basic_ios accessors (good(), fail(), etc.) for all possible combinations of ios_base::iostate flags:

ios_base::iostate flags			basic_ios accessors
eofbit	failbit	badbit	good()	fail()	bad()	eof()	operator bool	operator!
false	false	false	true	false	false	false	true	false
false	false	true	false	true	true	false	false	true
false	true	false	false	true	false	false	false	true
false	true	true	false	true	true	false	false	true
true	false	false	false	false	false	true	true	false
true	false	true	false	true	true	true	false	true
true	true	false	false	true	false	true	false	true
true	true	true	false	true	true	true	false	true

rdstate	returns state flags (public member function of std::basic_ios<CharT,Traits>)
setstate	sets state flags (public member function of std::basic_ios<CharT,Traits>)
clear	modifies state flags (public member function of std::basic_ios<CharT,Traits>)