streambuf::underflow

int underflow ( );

For the purpose of the streambuf class, underflows happen when a new character is to be read at the get pointer gptr, but this has reached the end pointer egptr, indicating that apparently no more characters are available in the internal input array.

This function is expected to modify the eback, gptr and egptr pointers that define the internal input array in such a way that if there are more characters available in the controlled input sequence after the location represented by streambuf::egptr, at least some of them are made available through this internal input array and the new character available at the get pointer's position itself is returned. Otherwise, if there are no more characters available in the controlled input sequence after the one represented by egptr, the function returns EOF (or traits::eof() for other traits).

This is a virtual member function that can be overriden for a specific behavior in derived classes. Its default behavior in streambuf is to do nothing and return EOF (or traits::eof() for other traits), but both standard derived classes, filebuf and stringbuf, override this function (see filebuf::underflow and stringbuf::underflow).

This protected member function is automatically called by sgetc member function when an underflow happens.

The definition of the member function uflow in streambuf relies on this member function. The behavior of uflow is the same as the one of underflow, except that it also advances the get pointer.

Parameters

none

Return Value

The new character available at the get pointer position, if any. Otherwise, EOF (or traits::eof() for other traits) is returned.

Basic template member declaration

( basic_streambuf<charT,traits> )


See also.