virtual int_type underflow();
The protected virtual member function endeavors to extract the current element c
from the input stream, and return the
element as T::
to_int_type
(c)
. It can do so in various ways:
c
as the element stored in the read position and advances the next pointer
for the input buffer. fgetc
(fp)
, and convert
them to an element c
of type E
by using the file conversion facet fac
to call fac.
in
as needed. If any read or
conversion fails, the function does not succeed.If the function cannot succeed, it returns T::
eof
()
. Otherwise, it returns c
, converted as described above.