Replacements for the C preprocessor [closed]

Question

I'm interested in using something other than the C preprocessor to preprocess my C and Objective-C source code. Are there good alternatives?

An example would be something that allowed one to escape out into a python or perl snippet in the middle of C code, and where the snippet spit out C that is then compiled as normal.

Answer 1

Cog isn't exactly a pre-processor, but it does go in-line in the code and generates stuff on the fly.

Answer 2

Sure, the standard C preprocessor is very limited.
I've done such a tool recently: https://github.com/d-ash/perlpp

For example this

<?
    my @types = ('char', 'int', 'long'); 
    foreach (@types) {
?>
        <?= $_ ?> read_<?= uc($_) ?>(<?= $_ ?>* v);
<?  } ?>

becomes this

char read_CHAR(char* v);
int read_INT(int* v);
long read_LONG(long* v);

Syntax is similar to PHP, but it uses Perl instead, and can capture texts into Perl stings.

Edit by cxw — With @d-ash's approval, I am also a maintainer of perlpp. If you have questions, feel free to drop me a line!

Answer 3

You can use your favourite programming language to build a script/tool to generate source files (.c/.cpp or .h, or whatever). Simply #include them or compile them into your project. It may help to have comments near the #include to identify what/where the tool is and what is generated.

This may not be as handy (or clean) as using a "real" preprocessor, but it would work. Then again, it really depends on your case.

Answer 4

I'd be interested to see what people come up with. I've tended to do small custom things with preprocessors written in Perl. It's easy to rig up a Makefile that calls the preprocessor. For example, here's a rule to call a program named 'meta' to generate 'file.c' from 'file.c.meta'.

% :: %.meta
    meta $< > $@

I'm doing fun things with 'meta' like generating custom fit C data structures. It's definitely a direction I'd suggest exploring. My hope is to eventually come up with a meta library roughly parallel to C++ templates.

Answer 5

If you're prepared to get your hands dirty with some C++, there's the Wave parser in Boost, which is built using the Spirit recursive descent parser. It's a complete C pre-processor that conforms to all the latest specs for C and C++ (and, by extension, Objective C, AFAICS).

It's highly modular so you can switch your own driver in that could do the extras you want.

http://www.boost.org/libs/wave/doc/introduction.html

Answer 6

The short answer is "no." The preprocessor is so intimately tied to the semantics of C that you can't really remove it, and in fact in some compilers isn't even a separate phase like it used to be in the old days --- compiling Objective C on a Mac just parses the Objective C syntax. So while you could certainly use another macro-processor, like m4, to process your source text before passing it to C, you wouldn't be eliminating the C preprocessor, you'd be adding another step of preprocessing.

But there's a deeper question here: what do you want to gain by eliminating the CPP phase?