1) Default constructor. Creates abasic_spanbuf that has no underlying buffer and is opened for both input and output. The pointers to get and put area are set to the null pointer value.

2) Same as(1), except that thebasic_spanbuf is opened in mode specified bywhich.

3) Creates abasic_spanbuf that manages the underlying buffer referenced bybuf (or has no underlying buffer ifbuf is empty) and is opened in mode specified bywhich. The pointers to get and put area are set as following, or to the null pointer value if not mentioned in the table:

Set bits in open mode (affecting pointers to get area)	Return value after setting
	eback()	gptr()	egptr()
std::ios_base::in	s.data()	s.data()	s.data()+ s.size()
Set bits in open mode (affecting pointers to put area)	Return value after setting
	pbase()	pptr()	epptr()
std::ios_base::out&&!std::ios_base::ate	s.data()	s.data()	s.data()+ s.size()
std::ios_base::out&&std::ios_base::ate	s.data()	s.data()+ s.size()	s.data()+ s.size()

4) Copy constructor is deleted.basic_spanbuf is not copyable.

5) Move constructor. Move-constructs thestd::basic_streambuf base subobject from that ofrhs. The pointers to get and put area, the open mode, and the underlying buffer (if any) are identical to those inrhs before construction.
It is implementation-defined whetherrhs still holds the underlying buffer after the move-construction.