size_t length

size_t length是implementation defined，因此，programmer不能够对其进行预期。

stackoverflow Is size_t the word size?

A

In the C++ standard, [support.types] (18.2) /6: "The type size_t is an implementation-defined unsigned integer type that is large enough to contain the size in bytes of any object."

This may or may not be the same as a "word size", whatever that means.