Effects:
Constructs an object of class
basic_istringstream<charT, traits>,
initializing the base class with
basic_istream(&sb)
and initializing sb with
basic_stringbuf<charT, traits, Allocator>(which | ios_base::in)) ([stringbuf.cons]).
Effects:
Constructs an object of class
basic_istringstream<charT, traits>,
initializing the base class with
basic_istream(&sb)
and initializing sb with
basic_stringbuf<charT, traits, Allocator>(str, which | ios_base::in)) ([stringbuf.cons]).