C pre-preprocessor or preprocessor replacement

Tischbein · 02-08-2007, 04:09 PM

Hello All,

Do any of you use either a non-standard C preprocessor or a pre-preprocessor? If so, could I take a show of hands of how many do and what kind of setup you use?

To clarify, this is an imaginary example in which bash is used as the pre-processing language:

Code:

#!/bin/generic_pre /bin/bash /usr/lib/generic_pre/bash_defs
#
#for i in alpha beta gamma
#do
#  DEFINE FUNCTION ${i}
#  DEFINE STRING \"${i}\"

   printf ("The function I am about to run is called " STRING "\n");
   FUNCTION;

#done

I know that the gcc preprocessor can do all sorts of clever tricks but there have on several occasions been times when I've not only wanted but I think, after careful consideration, NEEDED a better preprocessor. Making one is no big deal, but interoperability with other people doing the same thing seems a worthwhile goal.

I have a pretty good idea of what I think I want, but I don't know what's out there. There might even already be a generic way of using scripting languages for C preprocessing for all I know.

Regards, Hasenbein

gnashley · 02-09-2007, 08:59 AM

When you compile gcc there is an option for 'with-cpp' that will create a bash script which substitutes cpp -If I remember correctly.

grumpf · 02-10-2007, 09:20 AM

actualy it depends what you exspect. CPP is more or less and search/replace
that can easly be extended using bash/perl/awk; you name it.

When you expect help for a given problem maybe you should explain the
problem.

Tischbein · 02-11-2007, 11:38 AM

Here's a (second) toy problem:

Suppose I have a large program with lots of C files.

I have debugging code in all the files. Debug code is prefixed by DB and perhaps some ids, e.g.:

Code:

DB  printf(stderr, "Started on this file");
DB(3) printf(stderr, "doingstuff");
DB(anchor) printf(stderr, "doingotherstuff");
DB(3,anchor) printf(stderr, "never done this before!")

I have a .h file which controls debug output. Debugging can be switched on & off for each file, for each id, or for a combination of both:

Code:

DB_ON shluck.c 3  # db code in the indicated file at level 3.
DB_ON anchor      # db code with the anchor keyword

Finally, the code has to run fast, so the debug code really does have to be taken out by the preprocessor, not replaced by a C runtime check.

What tools does the C preprocessor have to help with this? Well, it has keywords for the current file name and it has concatenating ability. So it's pretty easy to make a runtime check for filenames:

#define DB if ( debug_##__FILE )

(or whatever it is - my trusty preprocessor manual is out of reach)
A couple of us put our heads together a few months ago (when I asked this one) and worked out how to deal with the keywords as well, and the result was really ugly. Also, it yet again involved runtime checks, so ran dog slow.

So, how do I do it using purely the pre-processor?

If I could use bash or perl as a preprocessing language I'd be happy.

I'll check the with-cpp option, thanks gnashley.
grumpfs: You mention that it's not only possible but easy to extend the pre-processor with other scripting languages. That sounds interesting. Can you show me some examples, or a page with a mini-essay on how to do this?

Regards, Hakenbein