29 Input/output library [input.output]

The class template basic_­istream defines a number of member function signatures that assist in reading and interpreting input from sequences controlled by a stream buffer.

Two groups of member function signatures share common properties: the formatted input functions (or extractors) and the unformatted input functions. Both groups of input functions are described as if they obtain (or extract) input characters by calling rdbuf()->sbumpc() or rdbuf()->sgetc().

They may use other public members of istream.

If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), then the input function, except as explicitly noted otherwise, completes its actions and does setstate(eofbit), which may throw ios_­base​::​failure ([iostate.flags]), before returning.

If one of these called functions throws an exception, then unless explicitly noted otherwise, the input function sets badbit in the error state.

If badbit is set in exceptions(), the input function rethrows the exception without completing its actions, otherwise it does not throw anything and proceeds as if the called function had returned a failure indication.