Re: Pointer to undeclared structure-type considered ok?

["Kevin P. Fleming" <kpfleming at starnetworks dot us>]

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.