offsetof(3C) — C LIBRARY FUNCTIONS
NAME
offsetof − offset of structure member
SYNOPSIS
#include <stddef.h>
size_t offsetof (type, member-designator);
DESCRIPTION
offsetof is a macro defined in stddef.h which expands to an integral constant expression that has type size_t, the value of which is the offset in bytes, to the structure member (designated by member-designator), from the beginning of its structure (designated by type).
— C Development Set