Offsetof (Using the GNU Compiler Collection (GCC)) (original) (raw)

6.12.6 Support for offsetof ¶

GCC implements for both C and C++ a syntactic extension to implement the offsetof macro.

primary: "__builtin_offsetof" "(" typename "," offsetof_member_designator ")"

offsetof_member_designator: identifier | offsetof_member_designator "." identifier | offsetof_member_designator "[" expr "]"

This extension is sufficient such that

#define offsetof(type, member) __builtin_offsetof (type, member)

is a suitable definition of the offsetof macro. In C++, typemay be dependent. In either case, member may consist of a single identifier, or a sequence of member accesses and array references.