Accessors

One very important rule: never use -> in an implementation (.c) file. (By the way, don't use the equivalent *. either.). Dereference operators should only appear in header (.h) files.

Instead, we use accessor macros to get dereference pointers (see the next section for the why). For example,


	/* This is the actual implementation */
	struct int_stack {
	  int		is_max;
	  int		is_len;
	  int *		is_vals;
	};

	#define deref_int_stack(_s)	(_s)

	#define x_max_int_stack(_s)	(deref_int_stack(_s)->is_max)
	#define x_len_int_stack(_s)	(deref_int_stack(_s)->is_len)
	#define x_vals_int_stack(_s)	(deref_int_stack(_s)->is_vals)

	#define max_int_stack(_s)	((void)0, x_max_int_stack(_s))
	#define len_int_stack(_s)	((void)0, x_len_int_stack(_s))
	#define vals_int_stack(_s)	((void)0, x_vals_int_stack(_s))

Note some syntactic idioms used:

There are several reasons for accessing fields using these multiple levels of macros.


Note:It turned out that a lot of people were under the misconception that _s was a reserved identifier. It is perfectly legal to use _s, or an identifier that begins with _[lower-case] as a macro parameter. See the standard, or the discussion on comp.lang.c


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