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From: scs@adam.pika.mit.edu (Steve Summit)
Newsgroups: comp.lang.c
Subject: Re: Prototyping char parameters in ANSI C
Message-ID: <10937@bloom-beacon.MIT.EDU>
Date: 29 Apr 89 03:04:28 GMT
References: <3950014@eecs.nwu.edu>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: scs@adam.pika.mit.edu (Steve Summit)
Lines: 43

In article <3950014@eecs.nwu.edu> gore@eecs.nwu.edu (Jacob Gore) writes:
>Is this valid ANSI C (or dpANS or whatever you want to call it):
>	void f(char);
>	void f(c)
>	char c;
>	{}
>
>The version of GNU cc I have complains:
>	t.c:5: argument `c' doesn't match function prototype
>	t.c:5: a formal parameter type that promotes to `int'
>	t.c:5: can match only `int' in the prototype
>Is this rule for real, or is this just a gcc bug?

Poor GNU!  They get asked this ALL THE TIME, they put in a three
line warning/explanation message, and people still don't get the
idea.

To recap, either use

	void f(int);		void f(char);
			or
	void f(c)		void f(char c)
	char c;			{}
	{}

The only difference is that the second form may allow the
argument not to be widened when passed, for those architectures
which support passing sub-word sized arguments.  (In either case,
c will act like a char within function f, being narrowed if
necessary, and having its effective address adjusted so that
something like

	f(c)
	char c;
	{
	write(1, &c, 1);
	}

works correctly on big-endian architectures.  Don't write that,
though; write(,,1) brings a machine to its knees.)

                                            Steve Summit
                                            scs@adam.pika.mit.edu