Does C have a NULL constant function?

[Thomas L.]

Hi all,
Does a "NULL constant function" exist in C? I mean:
I am searching for a C language constant which would be something like
a function but which would be translated by a compiler into "nothing":
no argument push in the stack pointer, no execution of the function
instructions, no cleaning up, nothing, nada, rien, vide...

I could then initialize a function pointer f to that constant function
and ask
(*f)(any_argume nt_list)
and the compiler would translate it and write in the text section:

*NOTHING*

I apologize if it seems "pathetical ly useless" but actually I would
find it the right tool to perform, for example,
(*MyVector->methods->NormalizeVecto r)(MyVector->info) if I know
MyVector is unit-length (so that it would not be modified by the
NormalizeVector function).
To perform the normalization is useless, time consuming and I am
exposed to rounding errors.

Any input appreciated
Thomas

[Dan Pop]

In <7d************ *************@p osting.google.c om> th************* @jrc.it (Thomas L.) writes:

Does a "NULL constant function" exist in C? I mean:
I am searching for a C language constant which would be something like
a function but which would be translated by a compiler into "nothing":
no argument push in the stack pointer, no execution of the function
instructions , no cleaning up, nothing, nada, rien, vide...

I could then initialize a function pointer f to that constant function
and ask
(*f)(any_argum ent_list)
and the compiler would translate it and write in the text section:

*NOTHING*

There is no such thing and you can't even use something like

void null(void) {}

for this purpose, because calling this function with a non-empty argument
list invokes undefined behaviour.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Ben Pfaff]

th************* @jrc.it (Thomas L.) writes:

Does a "NULL constant function" exist in C? I mean:
There's the null pointer constant. It's expressed as "0".
I am searching for a C language constant which would be something like
a function but which would be translated by a compiler into "nothing":
no argument push in the stack pointer, no execution of the function
instructions, no cleaning up, nothing, nada, rien, vide...

I could then initialize a function pointer f to that constant function
and ask
(*f)(any_argume nt_list)
and the compiler would translate it and write in the text section:

*NOTHING*

That's not what a null function pointer does. Instead,
invoking it yields undefined behavior. But you could get similar
behavior by testing whether the pointer is non-null:
if (f)
f(args);

--
"Welcome to the wonderful world of undefined behavior, where the demons
are nasal and the DeathStation users are nervous." --Daniel Fox

[Dave]

"Dan Pop" <Da*****@cern.c h> wrote in message
news:cd******** **@sunnews.cern .ch...

There is no such thing and you can't even use something like

void null(void) {}

What about
void null(...) { }

Is that valid C?

Dave

[Ben Pfaff]

"Dave" <vd*****@freema il.hu> writes:

void null(...) { }

Is that valid C?

No, varargs functions must have at least one fixed argument.
Otherwise what would you specify as the second argument to
va_start()?

Besides that, varargs functions are not compatible with
non-varargs functions.
--
Ben Pfaff
email: bl*@cs.stanford .edu
web: http://benpfaff.org

[Thomas L.]

Ben Pfaff <bl*@cs.stanfor d.edu> wrote in message news:<87******* *****@benpfaff. org>...

That's not what a null function pointer does. Instead,
invoking it yields undefined behavior. But you could get similar
behavior by testing whether the pointer is non-null:
if (f)
f(args);

Yes, sure.
But it's perhaps even less costy to point my pointer function with a
void *f(argument_lis t){}? (Perhaps some compilers can optimize this to
*noting*) There is compile-time type-checking, at run-time the passing
of argument on the stack is there, and I find it more "clean".

[Dan Weber]

Dave wrote:

"Dan Pop" <Da*****@cern.c h> wrote in message
news:cd******** **@sunnews.cern .ch...

There is no such thing and you can't even use something like

void null(void) {}

What about
void null(...) { }

Is that valid C?

Dave

Don't think so. What about void null(void) { NULL; } ?

Dan

[Jarno A Wuolijoki]

On Fri, 23 Jul 2004, Dan Weber wrote:

void null(void) {}

What about
void null(...) { }

Is that valid C?

Don't think so. What about void null(void) { NULL; } ?

This is an IAQ: http://www.plethora.net/~seebs/faqs/...html#section-4
;)