C++ named requirements: UnformattedInputFunction

Requirements

An UnformattedInputFunction is a stream input function that performs the following:

• Constructs an object of type basic_istream::sentry with automatic storage duration and with the noskipws argument set to true, which performs the following:

  • If eofbit or badbit are set on the input stream, sets the failbit as well, and if exceptions on failbit are enabled in this input stream's exception mask ((exceptions() & failbit) != 0), throws ios_base::failure.
  • Flushes the tie()'d output stream, if applicable.

• Checks the status of the sentry by calling sentry::operator bool(), which is equivalent to basic_ios::good.

  • If the operator returns false or sentry's constructor throws an exception:
    • Sets the number of extracted characters (gcount) in the input stream to zero.
    • If the function was called to write to an array of CharT, writes CharT() (the null character) to the first location of the array.
  • If the operator returns true, performs the input as if by calling rdbuf()->sbumpc() or rdbuf()->sgetc().
    • If the end of the stream is reached (the call to rdbuf()->sbumpc() or rdbuf()->sgetc() returns Traits::eof()), sets eofbit. If exceptions on eofbit are enabled in this stream's exception mask ((exceptions() & eofbit) != 0), throws ios_base::failure.
    • If an exception is thrown during input, sets badbit in the input stream. If exceptions on badbit are enabled in this stream's exception mask ((exceptions() & badbit) != 0), the exception is also rethrown.
      • Exceptions thrown from basic_ios::clear are not caught or rethrown.
    • If no exception was thrown during input, sets the number of extracted characters (gcount) in the input stream.

• In any event, whether terminating by exception or returning, the sentry's destructor is called before leaving this function.

Standard library

The following standard library functions are UnformattedInputFunctions.

• std::getline, except that it does not modify gcount.
• basic_istream::operator>>(basic_streambuf*)
• basic_istream::get
• basic_istream::getline
• basic_istream::ignore
• basic_istream::peek
• basic_istream::read
• basic_istream::readsome
• basic_istream::putback, except that it first clears eofbit
• basic_istream::unget, except that it first clears eofbit
• basic_istream::sync, except that it does not modify gcount
• basic_istream::tellg, except that it does not modify gcount
• basic_istream::seekg, except that it first clears eofbit and does not modify gcount
• std::ws, except that it does not modify gcount

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 61	C++98	it was unclear whether throwing an exception because of setting eofbit and/or failbit will result in setting badbit	exceptions thrown from basic_ios::clear are not caught or rethrown
LWG 160	C++98	the process of determining whether the exception caught is rethrown mentioned a non-existing function exception()	corrected to exceptions()
LWG 243	C++98	the behavior when sentry::operator bool() returns false or the sentry object fails to be constructed was not specified	specified