Nick Patavalis wrote:
In what sense is the "struct bar" type defined? Because if "struct bar" is not defined, then how can "struct bar *" be defined? Is it ok to to have pointer-type whose base type is not (or incompletely) defined?
This technique is used rather often to hide structure definitions from consumers of that structure. For example:
-- file foo.h --
struct foo;
extern struct foo *make_foo(void); extern void destroy_foo(struct foo *);
-- file foo.c --
struct foo {
int bar;
int baz;
char *bat;
struct foo *next;
}-- file foouser.c --
#include "foo.h"
static int do_the_work(void)
{
struct foo *here_it_is;here_it_is = make_foo(); ... destroy_foo(here_it_is); }
Simple, and works very well. All users of foo.h know that "struct foo" exists, and can store/retrieve pointers to one, and have functions to manipulate one. They just can't peek inside one.
