__CONCAT(3) - NetBSD Manual Pages

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__CONCAT(3)             NetBSD Library Functions Manual            __CONCAT(3)

__CONCAT, __STRING -- argument substitution
#include <sys/cdefs.h> xy __CONCAT(x, y); const char * __STRING(x);
The __CONCAT macro makes use of the cpp(1) preprocessor to concatenate two tokens. When the macro is expanded, x and y are combined into a sin- gle token, provided that the result forms a valid token; two tokens that together do not form a valid token can not be concatenated. This is known as ``token concatenation'' or ``token pasting''. The __STRING() macro uses the conventional `#' preprocessing operator to replace the argument x with a string literal. This is also known as ``stringification''.
The following two printf(3) calls produce the same output: #define Net 0x01 #define BSD 0x02 #define NetBSD "NetBSD" (void)printf("%s\n", __CONCAT(Net, BSD)); (void)printf("%s%s\n", __STRING(Net), __STRING(BSD));
cpp(1), cdefs(3)
The __CONCAT() and __STRING() macros first appeared in NetBSD 1.3.
Many small details direct the proper use of the macros. For example, while all leading and trailing whitespace is ignored when __STRING() is used, it is undefined whether cpp(1) puts white space between the tokens when __CONCAT() is used. It can be also noted that the C preprocessor converts all comments to whitespace before any macros are even consid- ered. The use of either macro is discouraged in complex constructs. Use of this macro is non-portable; this is part of the implementation namespace and should only be used in NetBSD code. NetBSD 9.1 October 17, 2013 NetBSD 9.1
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