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From: michael@stb.UUCP
Newsgroups: comp.lang.c
Subject: Re: Function prototypes versus open()
Message-ID: <1569@stb.UUCP>
Date: Fri, 5-Jun-87 00:51:42 EDT
Article-I.D.: stb.1569
Posted: Fri Jun  5 00:51:42 1987
Date-Received: Sun, 7-Jun-87 01:04:47 EDT
References: <18346@ucbvax.BERKELEY.EDU> <8042@utzoo.UUCP> <2210@hoptoad.uucp> <931@wjvax.wjvax.UUCP> <20119@sun.uucp>
Reply-To: michael@stb.UUCP (Michael)
Organization: STB BBS, La, Ca, USA, 90402, 213-459-7231
Lines: 66

In article <20119@sun.uucp> guy%gorodish@Sun.COM (Guy Harris) writes:
>> 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


Wait a sec. Would you please explain how the following can be done:

I have a dispatcher routine, that takes a pointer to a function, some args,
does some munching on the args, and calls the pointed to routine with 3,
4, or 5 args. Each routine called is expecting a known, fixed # of args,
yet the pointer used is with variable args. So, according to the above,
I have to declare the function pointer as variable args, which activates
one calling convention, yet the routines are fixed args, and expecting
another calling convention.
-- 
: Michael Gersten		seismo!scgvaxd!stb!michael
: The above is the result of being educated at a school that discriminates
: against roosters.