Class template
basic_syncbuf stores character data
written to it, known as the associated output, into internal
buffers allocated using the object's allocator
. The associated output is transferred to the
wrapped stream buffer object
*wrapped
when
emit() is called
or when the
basic_syncbuf object is destroyed
. Such transfers are atomic with respect to transfers
by other
basic_syncbuf objects
with the same wrapped stream buffer object
.