Standard C++ Library Reference ISO/IEC (VERSION3)

egptr(), a pointer just past the end of the buffer●
Similarly, an output buffer is characterized by:
pbase(), a pointer to the beginning of the buffer●
pptr(), a pointer to the next element to write●
epptr(), a pointer just past the end of the buffer●
For any buffer, the protocol is:
If the next pointer is null, no buffer exists. Otherwise, all three pointers point into the
same sequence. (They can be safely compared for order.)
●
For an output buffer, if the next pointer compares less than the end pointer, you can store
an element at the write position designated by the next pointer.
●
For an input buffer, if the next pointer compares less than the end pointer, you can read
an element at the read position designated by the next pointer.
●
For an input buffer, if the beginning pointer compares less than the next pointer, you can
put back an element at the putback position designated by the decremented next pointer.
●
Any protected virtual member functions you write for a class derived from
basic_streambuf<Elem, Tr> must cooperate in maintaining this protocol.
An object of class basic_streambuf<Elem, Tr> stores the six pointers described above.
It also stores a locale object in an object of type locale for potential use by a derived stream
buffer.
basic_streambuf::basic_streambuf
basic_streambuf();
The protected constructor stores a null pointer in all the pointers controlling the input buffer and
the output buffer. It also stores locale::classic() in the locale object.
basic_streambuf::char_type
typedef Elem char_type;
The type is a synonym for the template parameter Elem.
basic_streambuf::eback
char_type *eback() const;
The member function returns a pointer to the beginning of the input buffer.