__CONCAT(3)

NAME
__CONCAT, __STRING - argument substitution

SYNOPSIS
#include <sys/cdefs.h>
xy
__CONCAT(x, y);
const char *
__STRING(x);

DESCRIPTION
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 single 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”.

EXAMPLES
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));

SEE ALSO
cpp(1), cdefs(3)

HISTORY
The __CONCAT() and __STRING() macros first appeared in NetBSD 1.3.

CAVEATS
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 considered. 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.