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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: Function prototypes versus open()
Message-ID: <20119@sun.uucp>
Date: Mon, 1-Jun-87 15:49:44 EDT
Article-I.D.: sun.20119
Posted: Mon Jun  1 15:49:44 1987
Date-Received: Wed, 3-Jun-87 01:40:03 EDT
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> How about functions called with function pointers?  I am not that familiar
> with the details of function prototyping in the standard, but will it be
> possible to invoke functions with variable arguments with function pointers?

From the October 1, 1986 draft:

	3.5.3.3 Function declarators (including prototypes)

	...

	   Here are two more intricate examples:

		int (*apfi[3])(int *x, int *y);

	declares an array "apfi" of three pointers to functions returning
	"int".  Each of these functions has two parameters that are
	pointers to "int"....

which implies that the type of a function pointer, just like the type
of a function, includes the types of its arguments as well as the
type of its result.  As such, you can declare

	int (*pintvarargs)(int i, ...);

which is a pointer to a function whose first argument is an "int" and
which may have 0 or more optional arguments after that.  A function
pointed to by "pintvarargs" can be called with a variable-length list
of arguments, as long as that list has at least one argument and the
first argument is of a type that can be coerced to "int".  The
declaration

	int (*pintarg)(int i);

declares a pointer to a function whose *only* argument is an "int".
A function pointed to by "pintarg" may only be called with one
argument, which must be of a type that can be coerced to "int".

The deprecated old-style declaration

	int (*pwhoknows)();

is, I infer, equivalent to

	int (*pwhoknows)(...);

which declares a pointer to a function which may have 0 or more
optional arguments.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com