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.