104 lines
3.1 KiB
Groff
104 lines
3.1 KiB
Groff
.\" $NetBSD: __CONCAT.3,v 1.6 2010/12/16 10:40:04 jruoho Exp $ $
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.\"
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.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jukka Ruohonen.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd December 16, 2010
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.Dt __CONCAT 3
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.Os
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.Sh NAME
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.Nm __CONCAT ,
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.Nm __STRING
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.Nd argument substitution
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.Sh SYNOPSIS
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.In sys/cdefs.h
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.Ft xy
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.Fn __CONCAT "x" "y"
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.Ft const char *
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.Fn __STRING "x"
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.Sh DESCRIPTION
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The
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.Nm
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macro makes use of the
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.Xr cpp 1
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preprocessor to concatenate two tokens.
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When the macro is expanded,
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.Fa x
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and
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.Fa y
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are combined into a single token, provided that the result forms a valid token;
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two tokens that together do not form a valid token can not be concatenated.
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This is known as
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.Dq token concatenation
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or
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.Dq token pasting .
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.Pp
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The
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.Fn __STRING
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macro uses the conventional
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.Sq #
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preprocessing operator to replace the argument
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.Fa x
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with a string literal.
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This is also known as
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.Dq stringification .
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.Sh EXAMPLES
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The following two
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.Xr printf 3
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calls produce the same output:
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.Bd -literal -offset indent
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#define Net 0x01
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#define BSD 0x02
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#define NetBSD "NetBSD"
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(void)printf("%s\en", __CONCAT(Net, BSD));
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(void)printf("%s%s\en", __STRING(Net), __STRING(BSD));
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.Ed
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.Sh SEE ALSO
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.Xr cpp 1 ,
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.Xr cdefs 3
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.Sh HISTORY
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The
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.Fn __CONCAT
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and
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.Fn __STRING
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macros first appeared in
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.Nx 1.3 .
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.Sh CAVEATS
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Many small details direct the proper use of the macros.
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For example, while all leading and trailing whitespace is ignored when
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.Fn __STRING
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is used, it is undefined whether
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.Xr cpp 1
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puts white space between the tokens when
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.Fn __CONCAT
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is used.
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It can be also noted that the C preprocessor converts all
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comments to whitespace before any macros are even considered.
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The use of either macro is discouraged in complex constructs.
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