offsetof

Defined in header `<stddef.h>`
#define offsetof(type, member) /implementation-defined/

The macro offsetof expands to a constant of type size_t, the value of which is the offset, in bytes, from the beginning of an object of specified type to its specified member, including padding if any.

Language
headers
Type support
Dynamic memory management
Error handling
Program utilities
Variadic function support
Date and time utilities
Strings library
Algorithms
Numerics
Input/output support
Localization support
Thread support (C11)
Atomic operations (C11)
Technical Specifications

size_t
ptrdiff_t
NULL
max_align_t (since C11)
offsetof
Numeric limits