fill-pointer

(fill-pointer vector)

Returns the fill pointer of a vector created with make-array :fill-pointer. The fill pointer is the vector's effective length: length and printing stop at it, while aref can still reach the full backing storage. It is a setf place, so (setf (fill-pointer v) n) moves it to any position between 0 and the vector's total size. Signals an error when the array has no fill pointer (test with array-has-fill-pointer-p first).