incorrect warning?

[Duncan Muirhead]

When I compile the program below "Program start" with
gcc -std=c99 -pedantic -o bgcc bgcc.c
(where gcc --version gives
gcc (GCC) 3.4.5 20051201 (Red Hat 3.4.5-2)
Copyright (C) 2004 Free Software Foundation, Inc.
)
I get the warning
bgcc.c:3: warning: "struct thingTag" declared inside parameter list
bgcc.c:3: warning: its scope is only this definition or declaration, which
is probably not what you want

Should the code generate a warning? Is there a way to avoid it other than
adding
typedef struct thingTag * thingP;
and replacing line 3 with
typedef void (*show)( thingP);
(which does shut gcc up)?

TIA
Duncan

Program start
#include <stdio.h>

typedef void (*show)( struct thingTag *);

typedef struct thingTag
{ show f;
double v;
} thing;

void show_metres( thing* p)
{ printf( "%f m\n", p->v);
}

int main( int argc, char** argv)
{
thing T;
T.v = 1.7;
T.f = show_metres;
T.f( &T);
return 1;
}

[Chris Torek]

In article <pa************ *************** *@this.address>
Duncan Muirhead <no***@this.add ress> wrote:

If I understand [Keith Thompson] correctly, there is a special rule
for declarations of function (pointer) types ...
Not exactly. See the article I already referred you to elsewhere in
this thread.
As for typedefs for struct types, I suspect your right, but would say:
I, and indeed the people I've worked with, only ever use the typedef'd
names in code and so having the two names is limited to the type
declaration.

In that case, use the method I outlined in that same article.

Note that you can use the *same* name for the typedef-name and
the structure tag:

struct Foo;
typedef struct Foo Foo;

Note also that you can write "struct Foo;" (at file scope) as many
times as you like, while you can only have the typedef line once.
Hence, in some (relatively rare) situations, you *must* use only
the tag. For instance, if zog.h declares a prototype for a function
zog() that operates on a "Zog", while glik.h declares a prototype
for a function glik() that happens to take a "Zog" as an argument
but -- for whatever reason -- glik.h cannot #include "zog.h" nor
require that those who include glik.h also include zog.h first,
then glik.h must use "struct Zog" instead of "Zog:

/* glik.h */
struct Zog;
void glik(struct Zog *);

/* zog.h */
struct Zog;
typedef struct Zog Zog;

void zog(Zog *);

struct Zog {
Zog *next;
... other fields ...
};

(Of course, everything becomes much simpler if you just throw away
the typedef, and type out the word "struct". Then you no longer
need some sort of typographic gimmick -- in this case, the initial
capital letter -- to distinguish typedef-identifiers from other
ordinary identifiers. Not that a *compiler* needs such a gimmick,
but if you do not use one, programmers will make more mistakes.)
--
In-Real-Life: Chris Torek, Wind River Systems
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) [phone]
email: forget about it http://web.torek.net/torek/index.html
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