Emacs has a "c-macro-expand" function which is quite hackish but extremely useful, IMO: it attempts to macro expand the region.

For instance running it on the following code in the middle of a C source file:

    #define BOGO_MAX(a, b) a > b ? a : b

    int test()
    {
      return BOGO_MAX(3 + 4, 5);
    }

Creates a new buffer containing:

    int test()
    {
      return 3 + 4 > 5 ? 3 + 4: 5;
    }