Documentation for sub nativesizeof assembled from the following pages:

Language documentation: Native calling interface §

From Native calling interface

(Native calling interface) sub nativesizeof §

sub nativesizeof($obj) is export(:DEFAULT)

This returns the size in bytes of the supplied object, it can be thought of as being equivalent to sizeof in C. The object can be a builtin native type such as int64 or num64, a CArray or a class with the repr CStruct, CUnion or CPointer.