From the redhat web page:
http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/gcc/offsetof.html
__offsetof__ (expression)
is equivalent to the parenthesized expression, except that the
expression is considered an integral constant expression even if
it contains certain operators that are not normally permitted in
an integral constant expression. Users should never use
__offsetof__
directly; the only valid use of __offsetof__ is to implement the
offsetof macro in <stddef.h>.
To generate a diff of this commit:
cvs rdiff -r1.12 -r1.13 src/include/stddef.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.