1.\" $NetBSD: __CONCAT.3,v 1.6 2010/12/16 10:40:04 jruoho Exp $ $ 2.\" 3.\" Copyright (c) 2010 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Jukka Ruohonen. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd December 16, 2010 31.Dt __CONCAT 3 32.Os 33.Sh NAME 34.Nm __CONCAT , 35.Nm __STRING 36.Nd argument substitution 37.Sh SYNOPSIS 38.In sys/cdefs.h 39.Ft xy 40.Fn __CONCAT "x" "y" 41.Ft const char * 42.Fn __STRING "x" 43.Sh DESCRIPTION 44The 45.Nm 46macro makes use of the 47.Xr cpp 1 48preprocessor to concatenate two tokens. 49When the macro is expanded, 50.Fa x 51and 52.Fa y 53are combined into a single token, provided that the result forms a valid token; 54two tokens that together do not form a valid token can not be concatenated. 55This is known as 56.Dq token concatenation 57or 58.Dq token pasting . 59.Pp 60The 61.Fn __STRING 62macro uses the conventional 63.Sq # 64preprocessing operator to replace the argument 65.Fa x 66with a string literal. 67This is also known as 68.Dq stringification . 69.Sh EXAMPLES 70The following two 71.Xr printf 3 72calls produce the same output: 73.Bd -literal -offset indent 74#define Net 0x01 75#define BSD 0x02 76 77#define NetBSD "NetBSD" 78 79(void)printf("%s\en", __CONCAT(Net, BSD)); 80(void)printf("%s%s\en", __STRING(Net), __STRING(BSD)); 81.Ed 82.Sh SEE ALSO 83.Xr cpp 1 , 84.Xr cdefs 3 85.Sh HISTORY 86The 87.Fn __CONCAT 88and 89.Fn __STRING 90macros first appeared in 91.Nx 1.3 . 92.Sh CAVEATS 93Many small details direct the proper use of the macros. 94For example, while all leading and trailing whitespace is ignored when 95.Fn __STRING 96is used, it is undefined whether 97.Xr cpp 1 98puts white space between the tokens when 99.Fn __CONCAT 100is used. 101It can be also noted that the C preprocessor converts all 102comments to whitespace before any macros are even considered. 103The use of either macro is discouraged in complex constructs. 104