basic_filebuf::underflow
Extracts the current element from the input stream.
virtual int_type underflow( );
Return Value
If the function cannot succeed, it returns traits_type::eof. Otherwise, it returns ch, converted as described in the Remarks section.
Remarks
The protected virtual member function endeavors to extract the current element ch from the input stream, and return the element as traits_type::to_int_type(ch). It can do so in various ways:
If a read position is available, it takes ch as the element stored in the read position and advances the next pointer for the input buffer.
It can read one or more elements of type char*,* as if by successive calls of the form fgetc(fp), and convert them to an element ch of type Elem by using the file conversion facet fac to call fac.in as needed. If any read or conversion fails, the function does not succeed.
Requirements
Header: <fstream>
Namespace: std