Code:
#ifndef _ZLINE_H
#define _ZLINE_H
Nit... This violates the standard regarding reserved identifiers I believe:
7.1.3 Reserved identifiers
Each header declares or defines all identifiers listed in its associated subclause, and
optionally declares or defines identifiers listed in its associated future library directions
subclause and identifiers which are always reserved either for any use or for use as file
scope identifiers.
— All identifiers that begin with an underscore and either an uppercase letter or another
underscore are always reserved for any use.