$NetBSD: offsetof.3,v 1.4 2011/04/01 05:24:37 jruoho Exp $
$OpenBSD: offsetof.3,v 1.2 2010/02/18 18:30:19 jmc Exp $
Copyright (c) 2010 Thomas Pfaff <tpfaff@tp76.info>
Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.Dd April 1, 2011 .Dt OFFSETOF 3 .Os .Sh NAME .Nm offsetof .Nd offset of a structure member .Sh SYNOPSIS n stddef.h .Ft size_t .Fn offsetof "type" "member" .Sh DESCRIPTION The .Fn offsetof macro expands to an integer constant expression of type .Ft size_t and yields the offset, in bytes, of the field .Ar member from the start of the structure .Ar type .
$OpenBSD: offsetof.3,v 1.2 2010/02/18 18:30:19 jmc Exp $
Copyright (c) 2010 Thomas Pfaff <tpfaff@tp76.info>
Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.Dd April 1, 2011 .Dt OFFSETOF 3 .Os .Sh NAME .Nm offsetof .Nd offset of a structure member .Sh SYNOPSIS n stddef.h .Ft size_t .Fn offsetof "type" "member" .Sh DESCRIPTION The .Fn offsetof macro expands to an integer constant expression of type .Ft size_t and yields the offset, in bytes, of the field .Ar member from the start of the structure .Ar type .
p A compiler error will result if .Ar member is not aligned to a byte boundary (i.e. it is a bit-field). .Sh EXAMPLES Regardless of the architecture and the .Tn ABI , the following example prints the value zero for the variable .Va x . d -literal -offset indent 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\en", x, y, z); .Ed .Sh SEE ALSO .Xr __alignof__ 3 , .Xr stddef 3 , .Xr typeof 3 .Sh STANDARDS The .Fn offsetof macro conforms to .St -ansiC .