__CONCAT(3) - NetBSD Manual Pages

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__CONCAT(3)             NetBSD Library Functions Manual            __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 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''.


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 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 9.2                     October 17, 2013                     NetBSD 9.2