To show a underflow condition for a single character and increment the get pointer.

virtual int_type uflow();

The function uflow() is called when a character is not available for sbumpc().

The constraints are the same as underflow(), with the exceptions that the resultant character is transferred from the pending sequence to the back up sequence and the pending sequence may not be empty.

Calls underflow() and if traits::eof is not returned returns the integer value of the get pointer and increments the next pointer for input.