cpp/io/strstreambuf/underflow

Reads the next character from the get area of the buffer.

If the input sequence has a read position available (, returns.

Otherwise, if pptr is not null and (there is a put area and it is located after the get area), extends the end of the get area to include the characters that were recently written into the put area by incrementing egptr to some value between  and pptr, and then returns.

Otherwise, returns eof to indicate failure.

Parameters
(none)

Return value
The next character in the get area, on success, eof on failure