Aucbvax.5468
fa.unix-wizards
utzoo!decvax!ucbvax!unix-wizards
Sun Dec 13 22:53:22 1981
Perverse pointers...
>From decvax!yale-comix!hawley@Berkeley Sun Dec 13 22:52:12 1981
/* Chapter II from my new book --
 *
 *	"The last word on pointers to functions in C"
 *
 *		by mike hawley  (decvax!yale-comix!hawley)
 *
 * Pointers to functions in C can be really useful;
 * unfortunately, more people don't use them.
 * Some of you C hackers may get a charge out of this...
 */

main()
{
	int f();		/* f() returns my favorite integer.         */
	int (*fp)();		/* fp holds a pointer to a function like f  */
	int (*ret_f())();	/* ret_f() passes the pointer to "f()".     */
	long ret_f2();		/* Works like ret_f(), but must be coerced. */
	int (* (*ret_ret_f())())();   /* Horrors! */

	printf(" My favorite integer is: %d\n", f());

	fp = f;			/* The usual way to pass function pointers: */
	printf(" My favorite integer is: %d\n", (*fp)());

	fp = ret_f();		/* Another way to pass function pointers:   */
	printf(" My favorite integer is: %d\n", (*fp)());

	fp = (int(*)()) ret_f2();  /* Yet another way, using casts. */
	printf(" My favorite integer is: %d\n", (*fp)());

	fp = (*ret_ret_f())();	/* . .... Oh, come ON!! */
	printf(" My favorite integer is: %d\n", (*fp)());
}


f()		/* f() returns my favorite integer. */
{
	return (147);
}


int 
(*ret_f())() 	/* ret_f() returns f, a pointer to a function returning int. */
{
	int f();
	return (f);
}

long
ret_f2()	/* Does what ret_f() does, but requires the use of casts.    */
{
	int f();
	return ((long)f);
}

/* The following function returns a pointer to "ret_f", a function that
 *	returns a pointer to a function that returns an int.
 *	HA!  You know, the compiler even believes this!
 *	These critters are very shy; consequently, you don't see them 
 *	around too often!
 */
int
(* (*ret_ret_f())() )()
{
	int (*ret_f())();
	return (ret_f);
}

/* Why? A function like ret_f() can be used, for example, to select
 *	a command from a table of commands, and send back the pointer
 *	to the appropriate function for executing the chosen command.
 */

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 Bruce Jones, Henry Spencer, David Wiseman.