sunos man page for offsetof

offsetof(3C)						   Standard C Library Functions 					      offsetof(3C)

NAME
       offsetof - offset of structure member

SYNOPSIS
       #include <stddef.h>

       size_t offsetof(type, member-designator);

DESCRIPTION
       The offsetof() macro defined in <stddef.h> expands to an integral constant expression that has type size_t. The value of this expression is
       the offset in bytes to the structure member (designated by member-designator) from the beginning of its structure (designated by type).

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO
       attributes(5)

SunOS 5.10							    29 Dec 1996 						      offsetof(3C)