Yan <ro*****@gmail.com> writes:
Joona I Palaste wrote: mi************@asahq.com scribbled the following:
Hi,
I am wondering if something like this is possible?
#define COLON ":"
#define PERIOD "."
#define WORD "word"
#define WORD_COLON WORD+COLON
#define WORD_PERIOD WORD+PERIOD
...
I know the above is incorrect syntax. But is there a way to
concatenate the above strings in some way? I would rather not have to
define WORD_COLON as "word:" and WORD_PERIOD as "word.". I would like
to be able to change the value of WORD, with just modifying one
constant, rather than modifying all 3, as I am doing this on a much
larger scale.
The C compiler concatenates any adjacent string literals into a
single
string literal. Therefore
#define WORD_COLON WORD COLON
#define WORD_PERIOD WORD PERIOD
should do the trick.
you need the ## operator
i.e.:
#define concat(a, b) a ## b
and if you call it with:
concat(12,45), the pre-processor will replace it with 1245
The OP was trying to concatenate string literals. The ## operator is
valid only if the result is a single token. concat(12,45) does yield
the single token 1245, but concat("word",":") yields "word"":", which
is not a single token.
Joona was correct. Implicit string literal concatenation will do what
the OP wants; the ## operator (useful though it is for other things)
will not.
--
Keith Thompson (The_Other_Keith)
ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
