Re: trying to understand: "warning: function declaration isn't a prototype"

[Ingo Krabbe <ikrabbe.ask@web.de>]

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Am Donnerstag, 6. Juli 2006 11:21 schrieb Jay Vaughan:
> >Well, I explained why the warning is being emitted.
>
> Yes, because I haven't suppressed it with a switch .. but what I want
> to know is what the warning means.
>
> >Perhaps you could rephrase your question.  Or perhaps you could
> >provide the exact error message and the line in the source code to
> >which it refers.
>
> ../../common/Headers/msExtern.h:60: warning: function declaration
> isn't a prototype
>
> ------------------------------------
> msTypes.h (#included by msDefs.h):
> #define FAR
> #define FarPtr(type)  type FAR *
>
>
> ------------------------------------
> msDefs.h (#included by msExtern.h)
>
> typedef FarPtr(void)                TApplContextPtr;
>
>
> ------------------------------------
> msExtern.h:60:
>
> TApplContextPtr CreateApplContext ();
>
>
> ------------------------------------
> msLinux.c:
>
> TApplContextPtr CreateApplContext()
> {
>      LinuxContextPtr ptr =
>          (LinuxContextPtr) kmalloc(sizeof(LinuxContext), GFP_KERNEL);
>    //.. etc ..
>      return ptr;
> }
>
>
>
> The way I interpret this warning, its telling me that "FarPtr(void)
> CreatApplContext();" resolves to " * CreateApplContext();" .. clearly
> not a friendly prototype .. but which I suppose should probably be
> something more like (void) *CreateApplContext(); .. meaning I should
> fix the "#define FAR" to be "#define FAR void" instead ..

You might look at the results of the prototyping you can choose gcc -E 
some_file.c and see the result:

I attached xy.c.  The result of 

gcc -E xy.c | grep "typedef.*AbcPtr"             is
typedef void * AbcPtr;

which seems to be ok.

You should lookup if the definitions above are somehow hidden by conditionals, 
which you also can control via gcc -E.

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#include <stdio.h>

#define FAR
#define FarType(x) x FAR *
typedef FarType(void) AbcPtr;

extern AbcPtr func();

AbcPtr func()
{
	printf( "hello far ptr\n" );
	return (AbcPtr)NULL;
}

int main(int argc, char** argv)
{
	func();
	return 0;
}