netbsd man page for offsetof

OFFSETOF(3)						   BSD Library Functions Manual 					       OFFSETOF(3)

NAME
     offsetof -- offset of a structure member

SYNOPSIS
     #include <stddef.h>

     size_t
     offsetof(type, member);

DESCRIPTION
     The offsetof() macro expands to an integer constant expression of type size_t and yields the offset, in bytes, of the field member from the
     start of the structure type.

     A compiler error will result if member is not aligned to a byte boundary (i.e. it is a bit-field).

EXAMPLES
     Regardless of the architecture and the ABI, the following example prints the value zero for the variable x.

	   struct example {
		   double  x;
		   int	   y;
		   char    z;
	   };

	   size_t x, y, z;

	   x = offsetof(struct example, x);
	   y = offsetof(struct example, y);
	   z = offsetof(struct example, z);

	   (void)printf("%zu %zu %zu
", x, y, z);

SEE ALSO
     __alignof__(3), stddef(3), typeof(3)

STANDARDS
     The offsetof() macro conforms to ANSI X3.159-1989 (``ANSI C89'').

BSD
								   April 1, 2011							       BSD