2012-02-08 08:42:17 +00:00
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.\" $OpenBSD: offsetof.3,v 1.2 2010/02/18 18:30:19 jmc Exp $
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.\"
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.\" Copyright (c) 2010 Thomas Pfaff <tpfaff@tp76.info>
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" $FreeBSD$
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.\"
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2014-07-29 19:41:00 +00:00
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.Dd February 18, 2010
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2012-02-08 08:42:17 +00:00
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.Dt OFFSETOF 3
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.Os
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.Sh NAME
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.Nm offsetof
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.Nd offset of a structure member
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.Sh SYNOPSIS
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2013-06-04 07:37:06 +00:00
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.In stddef.h
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2012-02-08 08:42:17 +00:00
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.Ft size_t
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.Fn offsetof "type" "member"
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.Sh DESCRIPTION
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The
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.Fn offsetof
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macro expands to an integer constant expression of type
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.Ft size_t
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and yields the offset,
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in bytes, of the field
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.Ar member
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from the start of the structure
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.Ar type .
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.Pp
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A compiler error will result if
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.Ar member
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is not aligned to a byte boundary (i.e. it is a bit-field).
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.Sh STANDARDS
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The
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.Fn offsetof
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macro conforms to
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.St -ansiC .
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