Replacements for the C preprocessor [closed]

Answer 1

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 2

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?

Answer 3

You can use PHP as a C preprocessor. The advantages are:

• very similiar syntax, so syntax highlighting works.
• <? and ?> are not used in standard C (with non-standard C, the only thing that gets broken is old GCC extension operator that returns min/max)
• it's rich in libraries.
• it's turing complete.
• usage of macros is very explicit. (compared to sneaky C preprocessor macros)

For serious use though, making PHP print the #line directives is needed for debugging preprocessed code.

<?php include_once "stdio.h"; ?>

int main()
{
    <?php
        for($i = 0; $i < 20; $i++)
            echo 'printf("%d\n", '.$i.');';
    ?>
}

Answer 4

I see a 2001 paper introducing a python-like pre-processor http://ray.cg.tuwien.ac.at/rft/Papers/PYM/pym.html. It's not clear that anyone is using it..

Answer 5

The idea that you run code, the result of which is then spliced in is called quasiquotation. The code you run is antiquoted.

I know how to solve this problem using Lua. I've used string.gsub with an antiquotation function I wrote myself. I've used shell syntax for the antiquotation. As in the shell the antiquoted code returns a string which is then spliced into the code.

Below prog is the C code with antiquoted text, and antiquote is the antiquotation function. I've used Lua's special string quoting double square brackets to full advantage. In practice you wouldn't do this; you'd put prog in a separate file.

names = { 'John', 'Paul', 'George', 'Ringo' }

local prog = [===[
#include <stdio.h>

main() {
  $(local out = { }
    for _, n in ipairs(names) do
      table.insert(out, string.format([[  printf("The name is %%s\n", %q);]], n))
    end
    return table.concat(out, '\n  ')
   )
}
]===]


local function antiquote(s)
  local body = s:match '^%$%((.*)%)$'
  return assert(loadstring(body))()
end

prog = prog:gsub('%$%b()', antiquote)
io.stdout:write(prog)

In use, the program looks like this:

: nr@curlycoat 1181 ; lua /home/nr/tmp/emit-c.lua
#include <stdio.h>

main() {
    printf("The name is %s\n", "John");
    printf("The name is %s\n", "Paul");
    printf("The name is %s\n", "George");
    printf("The name is %s\n", "Ringo");
}

Answer 6

If you abstract your problem a bit, then you are in fact looking for a templating engine for your code. Just as most websites inserts dynamically generated content in static templates, you want to insert dynamically generated code into your program.

I currently use Jinja2 (Python) for most templating work - I've found it to be very configurable in every way.