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## 6 Representation of #define and #undef

This section describes the stabs support for macro define and undefine information, supported on some systems. (e.g., with `-g3` `-gstabs` when using GCC).

A `#define macro-name macro-body` is represented with an `N_MAC_DEFINE` stab with a string field of `macro-name macro-body`.

An `#undef macro-name` is represented with an `N_MAC_UNDEF` stabs with a string field of simply `macro-name`.

For both `N_MAC_DEFINE` and `N_MAC_UNDEF`, the desc field is the line number within the file where the corresponding `#define` or `#undef` occurred.

For example, the following C code:

        #define NONE	42
        #define TWO(a, b)	(a + (a) + 2 * b)
        #define ONE(c)	(c + 19)

        main(int argc, char *argv[])
        {
          func(NONE, TWO(10, 11));
          func(NONE, ONE(23));

        #undef ONE
        #define ONE(c)	(c + 23)

          func(NONE, ONE(-23));

          return (0);
        }

        int global;

        func(int arg1, int arg2)
        {
          global = arg1 + arg2;
        }

produces the following stabs (as well as many others):

        .stabs	"NONE 42",54,0,1,0
        .stabs	"TWO(a,b) (a + (a) + 2 * b)",54,0,2,0
        .stabs	"ONE(c) (c + 19)",54,0,3,0
        .stabs	"ONE",58,0,10,0
        .stabs	"ONE(c) (c + 23)",54,0,11,0

NOTE: In the above example, `54` is `N_MAC_DEFINE` and `58` is `N_MAC_UNDEF`.