I've been a C programmer, with some C++ exposure...I guess I don't understand whats wrong with :

keyx.akeyf = new (void (*[keyx.numf])());

Shouldn't that return:
(english parsing logic: (from my C memory))

start innermost : an array, size keyx.numf
go left to parens: of pointers
hit parens: to functions
hit parens: that return void?

Michael

"Heinz Saathoff" <hsaat@bre.ipnet.de> wrote in message news:MPG.1773b308bc716a039896a1@news.digitalmars.com...
> E. Trelmar schrieb...
> > keyx.akeyf = new (void (*[keyx.numf])());
> > Using a constant in place of keyx.numf removes the error, however, I
can't use a
> > constant in this case, I need a variable.
> > If anyone can point out the proper syntax I'd appreciate it.
>
> Seems DMC has a problem here. But there is a workaround! I assume that akeyf is declared like this:
>
>   struct {
>      //... something else
>      void (**akeyf)();
>   } keyx;
>
> Instead of
>
>    keyx.akeyf = new (void (*[keyx.numf])());
>
> that should be correct you can introduce a typedef:
>
>   typedef void (*FUNC_PTR)();
>   keyx.akeyf = new FUNC_PTR[keyx.numf];
>
> Now DMC compiles!
>
>
> Regards,
> Heinz

"Heinz Saathoff" <hsaat@bre.ipnet.de> wrote in message news:MPG.1773f18cf61e8a219896a3@news.digitalmars.com...
>    new-expression:
>        new new-placement_opt  new-type-id  new-initializer_opt
>        new new-placement_opt  ( new-type-id ) new-initializer_opt
>
> Note the second form with explicit parenthesis. Without the optional new-initializer the new expression ends at the closing ')'. The usual higher prceeding of [] does not apply because it can only by applied to an object in a new expression. The opject is what new returns.

Right, thanks!  What fooled me is that when you write "new unsigned int[100]", you get what you'd expect...

> > But that's indeed a good proof that just if
> > you *can* do something, it doesn't mean it's also a good idea to do
it...
> > such code is almost unreadable!  I also think the typedef solution is
clean
> > and easy to understand, and it should be always used in such cases.
>
> > About BCC: it complains it cannot assign a void(*)() to a void(**)()
without
> > cast.  No comment!
>
> BCC is right here!

Yes, it seems so, I tried today with Comeau, and it says the same.  And it
also compiles the original syntax:
new (void(*[100])()), just as gcc.  So, it seems like another bug in DMC?

> > > New expressions with complicated types are a bit tricky and not so
easy
> > > to understand.
> >
> > That's right!  After all, there's a good reason why typedef exists in
the
> > language, and probably ISO-C++ comittee will also add templatized
typedefs -
> > so it shouldn't be considered an obsolete feature.  :)
>
> What do you mean with templatized typedefs?

Something like:
template<typename T>
typedef vector<T> vt;

vt<int> vec_int;  // stupid example, and illegal for now...

With current standard, you have to do:

template<typename T>
struct X
{
  typedef vector<T> vt;
};

X<int>::vt vec_int;

Stuff like this seems to be used a lot in Loki library (Andrei Alexandrescu), and I read in CUJ they are serious about adding templatized typedefs to standard.

Best regards,
  Laurentiu

So in other words, if he wants to have an array of function pointers...

new ( ( void * ) () ) [ size ];
Might actually work...
However this probably will not work with other compilers...

Because of the 'confusion' about this among the different compilers I prefer to use a typedef anyways.

Consider this:

typedef char *  pchar;

new char [ size ];
new pchar [ size ];
new ( pchar ) [ size ];
new ( char * ) [ size ];

I have no idea why the 'commitee' or who ever is was got such a simple thing
wrong...
new TYPE [ SIZE ];
How much easier could it have been?
I mean, what makes more sense: new ( char * ) [ size ]; or new ( char * [ size ]
);??? <g>

I guess one more reason to go with D!

Jan



Jan Knepper wrote:

> He wasn't very clear in his example... No typedefs or anything.
> In basic the 'new' when wrong because he used different syntax as I tried to
> explain:
> new ( type* ) [ size ]; instead of new ( type * [ size ] );
> I think the latter will not work with DMC++
>
> Jan
>
> Heinz Saathoff wrote:
>
> > Jan Knepper schrieb...
> > > > keyx.akeyf = new (void (*[keyx.numf])());
> > >
> > > Try:
> > > keyx.akeyf = new ( void * ) [ keyx.numf ];
> >
> > Hi Jan, that's not the same! E. Trelmars new expression should result in
> > a array of pointer to function returning void.
> > Your Expression would result in ONE void pointer-pointer that is
> > immediatly indexed with keyx.numf resulting in an uninitialized void
> > pointer.
> >
> > Regards,
> >         Heinz

> Yes, it seems so, I tried today with Comeau, and it says the same.  And it
> also compiles the original syntax:
> new (void(*[100])()), just as gcc.  So, it seems like another bug in DMC?

DMC++ has been known to be different on this (more sensible I would call it!)
for years!
I questioned this years ago in the Symantec newsgroups and Walter himself
replied with something like:
"We have been known to be different at times"

Jan

DigitalMars schrieb...
> 
> keyx.akeyf = new (void (*[keyx.numf])());
> 
> Shouldn't that return:
> (english parsing logic: (from my C memory))
> 
> start innermost : an array, size keyx.numf
> go left to parens: of pointers
> hit parens: to functions
> hit parens: that return void?

absolute correct! That's what the new expressoin should return, only that the array is converted to a pointer to the first element of the allocated array.

Regards,
	Heinz

Jan Knepper schrieb...
> > Yes, it seems so, I tried today with Comeau, and it says the same.  And it
> > also compiles the original syntax:
> > new (void(*[100])()), just as gcc.  So, it seems like another bug in DMC?
> 
> DMC++ has been known to be different on this (more sensible I would call it!)
> for years!

Nice said :-)

> I questioned this years ago in the Symantec newsgroups and Walter himself
> replied with something like:
> "We have been known to be different at times"

So what's the difference between different and bug?


Regards,
	Heinz

Jan Knepper schrieb...
> So in other words, if he wants to have an array of function pointers...

That's what I expected from his original statement.

> new ( ( void * ) () ) [ size ];
> Might actually work...
> However this probably will not work with other compilers...

... more standard conforming compilers


> Because of the 'confusion' about this among the different compilers I prefer to use a typedef anyways.

This can be helpfull in complex declarations


> Consider this:
> 
> typedef char *  pchar;
> 
> new char [ size ];
> new pchar [ size ];
> new ( pchar ) [ size ];
> new ( char * ) [ size ];
> 
> I have no idea why the 'commitee' or who ever is was got such a simple thing
> wrong...
> new TYPE [ SIZE ];
> How much easier could it have been?
> I mean, what makes more sense: new ( char * ) [ size ]; or new ( char * [ size ]
> );??? <g>

I also don't know why the second form of new with new ( type ) is
neccessary and beaving different. Originally I also expected both
declarations the same as you normally can add parenthesis to make things
clearer.
But not everywhere, as in

   func(int);        // 1
   func(int, int);   // 2
   //...
   func(1,2);        // 2 called
   func((1,2));      // 1 called !?

So sometimes adding parenthesis results in different behaviour.


Regards,
	Heinz


> 
> I guess one more reason to go with D!

> > DMC++ has been known to be different on this (more sensible I would call it!)
> > for years!
> Nice said :-)

Thanks!

> > I questioned this years ago in the Symantec newsgroups and Walter himself
> > replied with something like:
> > "We have been known to be different at times"
> So what's the difference between different and bug?

I would not know...
different is different, a bug is a bug... <g>

Jan