1799a00c0SKevin Lo.\" $OpenBSD: offsetof.3,v 1.2 2010/02/18 18:30:19 jmc Exp $ 2799a00c0SKevin Lo.\" 3799a00c0SKevin Lo.\" Copyright (c) 2010 Thomas Pfaff <tpfaff@tp76.info> 4799a00c0SKevin Lo.\" 5799a00c0SKevin Lo.\" Permission to use, copy, modify, and distribute this software for any 6799a00c0SKevin Lo.\" purpose with or without fee is hereby granted, provided that the above 7799a00c0SKevin Lo.\" copyright notice and this permission notice appear in all copies. 8799a00c0SKevin Lo.\" 9799a00c0SKevin Lo.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10799a00c0SKevin Lo.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11799a00c0SKevin Lo.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12799a00c0SKevin Lo.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13799a00c0SKevin Lo.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14799a00c0SKevin Lo.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15799a00c0SKevin Lo.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16799a00c0SKevin Lo.\" 17799a00c0SKevin Lo.\" $FreeBSD$ 18799a00c0SKevin Lo.\" 19799a00c0SKevin Lo.Dd February 18 2010 20799a00c0SKevin Lo.Dt OFFSETOF 3 21799a00c0SKevin Lo.Os 22799a00c0SKevin Lo.Sh NAME 23799a00c0SKevin Lo.Nm offsetof 24799a00c0SKevin Lo.Nd offset of a structure member 25799a00c0SKevin Lo.Sh SYNOPSIS 26*580dbd65SJoel Dahl.In stddef.h 27799a00c0SKevin Lo.Ft size_t 28799a00c0SKevin Lo.Fn offsetof "type" "member" 29799a00c0SKevin Lo.Sh DESCRIPTION 30799a00c0SKevin LoThe 31799a00c0SKevin Lo.Fn offsetof 32799a00c0SKevin Lomacro expands to an integer constant expression of type 33799a00c0SKevin Lo.Ft size_t 34799a00c0SKevin Loand yields the offset, 35799a00c0SKevin Loin bytes, of the field 36799a00c0SKevin Lo.Ar member 37799a00c0SKevin Lofrom the start of the structure 38799a00c0SKevin Lo.Ar type . 39799a00c0SKevin Lo.Pp 40799a00c0SKevin LoA compiler error will result if 41799a00c0SKevin Lo.Ar member 42799a00c0SKevin Lois not aligned to a byte boundary (i.e. it is a bit-field). 43799a00c0SKevin Lo.Sh STANDARDS 44799a00c0SKevin LoThe 45799a00c0SKevin Lo.Fn offsetof 46799a00c0SKevin Lomacro conforms to 47799a00c0SKevin Lo.St -ansiC . 48