Preprocessing & #error

Preprocessing & #error

[Alex Vinokur]

Here is some code.

====== C code : foo.c : BEGIN ======
#define ITEM1 100
#define ITEM2 200
#if (ITEM1 != ITEM2)
#error BUG : ITEM1 != ITEM2
#endif
====== C code : foo.c : END ========

====== Compilation (Preprocessing) : BEGIN ======

$ gcc -v
[---omitted---]
gcc version 3.3.1 (cygming special)

$ gcc foo.c
foo.c:4:2: #error BUG : ITEM1 != ITEM2

====== Compilation (Preprocessing) : END ========


I would like to get the following output :
$ gcc foo.c
foo.c:4:2: #error BUG : 100 != 200


Is it possible?


   =====================================
   Alex Vinokur
     mailto:alexvn@connect.to
     http://mathforum.org/library/view/10978.html
   =====================================

Re: Preprocessing & #error

[Eljay Love-Jensen]

Hi Alex,

>Is it possible?

It is POSSIBLE, but you'd have to write your own pre-pre-processor.  (Perhaps in Perl?)

Without doing to that extra-ordinary effort, it isn't possible with the pre-processor.  AFAIK.

Or you could change the line to read...
#error BUG : 100 != 200
...but I presume that defeats the intent of having the token macro-expanded.

You could also modify your GCC to perform macro expansion on the error line.  That may be more effort than writing your own pre-pre-processor (unless you are already familiar with GCC internals).  And you'd have a custom one-off pre-processor in your GCC.

Pre-processor info here <http://www.delorie.com/gnu/docs/gcc/cpp_62.html>.

HTH,
--Eljay