cpp/named req/UnformattedInputFunction

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

@1@ Constructs an object of type with automatic storage duration and with the  argument set to, which performs the following: @2@ Checks the status of the sentry by calling, which is equivalent to.
 * If or  are set on the input stream, sets the  as well, and if exceptions on  are enabled in this input stream's exception mask, throws.
 * Flushes the tie'd output stream, if applicable.
 * If the operator returns 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, writes (the null character) to the first location of the array.


 * If the operator returns, performs the input as if by calling or.
 * If the end of the stream is reached (the call to or  returns ), sets . If exceptions on  are enabled in this stream's exception mask, throws.
 * If an exception is thrown during input, sets in the input stream. If exceptions on  are enabled in this stream's exception mask, the exception is also rethrown.
 * Exceptions thrown from are not caught or rethrown.
 * If no exception was thrown during input, sets the number of extracted characters (gcount) in the input stream.

@3@ 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 s.


 * std, except that it does not modify gcount.
 * , except that it first clears
 * , except that it first clears
 * , except that it does not modify gcount
 * , except that it does not modify gcount
 * , except that it first clears and does not modify gcount
 * std, except that it does not modify gcount
 * , except that it first clears
 * , except that it first clears
 * , except that it does not modify gcount
 * , except that it does not modify gcount
 * , except that it first clears and does not modify gcount
 * std, except that it does not modify gcount
 * std, except that it does not modify gcount