offsetof(3) Linux Programmer's Manual offsetof(3) NAME offsetof - find offset in a structure SYNOPSIS #include <stddef.h> size_t offsetof(type, member); DESCRIPTION offsetof returns the offset in bytes of member within type. The result is an integer constant expression with type size_t. member must not be a bit field. EXAMPLE struct s { int a; int b; }; printf("offset of a = %zu\n", offsetof(struct s, a)); printf("offset of b = %zu\n", offsetof(struct s, b)); The offset of a will be 0, but the offset of b will depend on the size of int and on the platform's alignment rules. CONFORMING TO ISO/IEC 9899 2005-01-25 offsetof(3)