typedef void foo_t()

[Alex Vinokur]

How does typedef work for foo2_t?

What can one do with foo2_t?

------ bar.c ------
void foo() {}

typedef void (*foo1_t)();
typedef void foo2_t(); /* How does typedef work here? */

int main()
{
foo1_t foo1 = foo;
foo2_t foo2 = foo; /* Line 9 */
return 0;
}
-------------------

GNU gcc 4.0.1

bar.c: In function `main':
bar.c:9: error: function `foo2' is initialized like a variable


--
Alex Vinokur
email: alex DOT vinokur AT gmail DOT com

http://mathforum.org/library/view/10978.html

http://sourceforge.net/users/alexvn

[Richard Tobin]

Re: typedef void foo_t()

In article <dnbrtt$1ee$1@d omitilla.aioe.o rg>,
Alex Vinokur <alexvn@users.s ourceforge.net> wrote:
[color=blue]
>typedef void foo2_t(); /* How does typedef work here? */[/color]
....[color=blue]
>foo2_t foo2 = foo; /* Line 9 */[/color]

This would be legal:

foo2_t *foo2 = foo;

-- Richard

[Richard Heathfield]

Re: typedef void foo_t()

Alex Vinokur said:
[color=blue]
> How does typedef work for foo2_t?
>
> What can one do with foo2_t?
>
> ------ bar.c ------
> void foo() {}
>
> typedef void (*foo1_t)();[/color]

This means that

foo1_t x;

is a declaration that x is a pointer to a function taking unknown arguments
and returning void.
[color=blue]
> typedef void foo2_t(); /* How does typedef work here? */[/color]

This means that

foo2_t y;

is a declaration that y is a function taking unknown arguments and returning
void.

Because it's a function, it can't be instantiated in the same way an object
can. Nevertheless, this is a useful technique. If the topic cops can just
hold their fire for a second...

typedef LRESULT RJH_MESSAGE_HAN DLER(HWND,
UINT,
WPARAM,
LPARAM);

RJH_MESSAGE_HAN DLER DebuggerCreate;
RJH_MESSAGE_HAN DLER DebuggerDestroy ;
RJH_MESSAGE_HAN DLER DebuggerReset;
RJH_MESSAGE_HAN DLER DebuggerDisplay ;

is valid C, and (arguably) is neater than:

LRESULT DebuggerCreate( HWND, UINT, WPARAM, LPARAM);
LRESULT DebuggerDestroy (HWND, UINT, WPARAM, LPARAM);
LRESULT DebuggerReset(H WND, UINT, WPARAM, LPARAM);
LRESULT DebuggerDisplay (HWND, UINT, WPARAM, LPARAM);

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)

[Niklas Norrthon]

Re: typedef void foo_t()

Richard Heathfield <invalid@invali d.invalid> writes:
[color=blue]
> Alex Vinokur said:
>[color=green]
> > How does typedef work for foo2_t?
> >
> > What can one do with foo2_t?
> >
> > ------ bar.c ------
> > void foo() {}
> >
> > typedef void (*foo1_t)();[/color]
>
> This means that
>
> foo1_t x;
>
> is a declaration that x is a pointer to a function taking unknown arguments
> and returning void.
>[color=green]
> > typedef void foo2_t(); /* How does typedef work here? */[/color]
>
> This means that
>
> foo2_t y;
>
> is a declaration that y is a function taking unknown arguments and returning
> void.
>
> Because it's a function, it can't be instantiated in the same way an object
> can. Nevertheless, this is a useful technique. If the topic cops can just
> hold their fire for a second...[/color]

I don't see anything in what you write that could be considered off topic, so
no need to ask the topic cops to shut up... (And I haven't written one single
line of code for windows apps in more than five years).
[color=blue]
> typedef LRESULT RJH_MESSAGE_HAN DLER(HWND,
> UINT,
> WPARAM,
> LPARAM);
>
> RJH_MESSAGE_HAN DLER DebuggerCreate;
> RJH_MESSAGE_HAN DLER DebuggerDestroy ;
> RJH_MESSAGE_HAN DLER DebuggerReset;
> RJH_MESSAGE_HAN DLER DebuggerDisplay ;[/color]

Interesting. I've never used function declaration like these, and I agree that
they could be prefered in some situations...

/Niklas Norrthon

[Richard Heathfield]

Re: typedef void foo_t()

Niklas Norrthon said:
[color=blue]
> Richard Heathfield <invalid@invali d.invalid> writes:
>[color=green]
>> typedef LRESULT RJH_MESSAGE_HAN DLER(HWND,
>> UINT,
>> WPARAM,
>> LPARAM);
>>
>> RJH_MESSAGE_HAN DLER DebuggerCreate;
>> RJH_MESSAGE_HAN DLER DebuggerDestroy ;
>> RJH_MESSAGE_HAN DLER DebuggerReset;
>> RJH_MESSAGE_HAN DLER DebuggerDisplay ;[/color]
>
> Interesting. I've never used function declaration like these, and I agree
> that they could be prefered in some situations...[/color]


I forgot to say earlier that I actually prefer to typedef function types
rather than function pointer types, because:

void foo(RJH_MESSAGE _HANDLER *fptr)
{
... whatever ...
}

reminds me that I'm dealing with a pointer type. I don't like hiding
pointers with typedef. Just a style thing really.


--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)