The "E" switch of gcc tells it to do only pre-processing and then stop. Output is to standard output, so you will want to capture that in a file.

However, the pre-processor goes all the way and resolves all macros, leaving no trace of them anymore. Its output is:

void main()
{
 int a, b, c;
 float d,e,f;

  c = a+b;

   f = e*d;
}

[download]
Actually it is much longer, related to the stdio.h and stdlib.h files.

And that is exactly where your problems will be: you will have to write a dedicated pre-processor which goes to all the included files to see which macros are and remain undefined (macros can be anywhere, not just in your header files) and then parse all files to see which code is to be deleted, leaving all other macro references in place.

Of course your example is trivial, but once you have many #if and #ifdef tests deeply nested, parsing the .c files will become more and more complicated. It will no longer be a straight search-and-delete thing, but you will actually have to parse what you are handling.

Anyhow, have a look at Text::EP3. It is an extensible pre-processor written in Perl, so you may be able to adapt it to your needs.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

My blog: Imperial Deltronics

In reply to Re: C macro pre processing by CountZero
in thread C macro pre processing by prassi

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.