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How do I overload functions in C?

I know that C++ lets you overload functions, but how do I overload functions in C?
Nov 13 '05
13 44219
On 2003-10-13, some one <fr********@yah oo.com> wrote:
I know that C++ lets you overload functions, but how do I overload
functions in C?


You cannot do so arbitrarily, all C solutions require some form of
trickery. Several have been offered to you.

One trickery not yet suggested is to employ a polymorphic interface.

typedef struct polymorph polymorph;
struct polymorph {
void (* const foo)(polymorph *);
};

void foo(polymorph *p) { p->foo(p); }
Now, you get a form of function overloading when you create instances
of polymorph.

struct A {
polymorph interface;
int a;
};

static void A_foo(polymorph *p) {
struct A *me = (void *)p;
printf("a:%d\n" , a++);
}

static const polymorph A_interface = { A_foo };

polymorph * create_A(void) {
struct A *i = malloc(sizeof(s truct A));
i->interface = A_interface;
i->a = 0;
}

struct B {
polymorph interface;
int b;
};

static void B_foo(polymorph *p) {
struct B *me = (void *)p;
printf("b:%d\n" , b--);
}

static const polymorph B_interface = { B_foo };

polymorph * create_B(void) {
struct B *i = malloc(sizeof(s truct B));
i->interface = B_interface;
i->b = 0;
}

Now, you can get a form of overloading with the foo() function.

polymorph *a = create_A(); /* a points to a struct A */
polymorph *b = create_B(); /* b points to a struct B */

foo(a); /* will output "a:0" */
foo(b); /* will output "b:0" */
foo(a); /* will output "a:1" */
foo(b); /* will output "b:-1" */

-- James
Nov 13 '05 #11
jacob navia wrote:
With lcc-win32 you write:

[stuff that isn't C and isn't topical in comp.lang.c]

--
Martin Ambuhl

Nov 13 '05 #12

"Arthur J. O'Dwyer" <aj*@nospam.and rew.cmu.edu> wrote in message
news:Pi******** *************** ************@un ix46.andrew.cmu .edu...

On Mon, 13 Oct 2003, jacob navia wrote:

"some one" <fr********@yah oo.com> wrote [...]
I know that C++ lets you overload functions, but how do
I overload functions in C?


With lcc-win32 you write:
int overloaded fn(struct a*arg);
int overloaded fn(struct b *arg);

and when you pass to fn an "a" it will call the first, and when you
pass it the second it will call the second.

http://www.cs.virginia.edu/~lcc-win32


That's very interesting, Jacob, but the OP did ask about
the C language, not about lcc-win32.

Oh, and *please* don't top-post.

-Arthur

OK OK True, this is an lcc-win32 evil extension...
Sorry, I couldn't resist :-)
If this question arises it is because people need that isn't it?
Nov 13 '05 #13
"jacob navia" <ja*********@ja cob.remcomp.fr> wrote in message news:<bm******* ***@news-reader4.wanadoo .fr>...
"Arthur J. O'Dwyer" <aj*@nospam.and rew.cmu.edu> wrote in message
news:Pi******** *************** ************@un ix46.andrew.cmu .edu...

That's very interesting, Jacob, but the OP did ask about
the C language, not about lcc-win32.

Oh, and *please* don't top-post.

-Arthur
OK OK True, this is an lcc-win32 evil extension...


Not evil, just off-topic. It isn't polite to post things outside of
the topic in a newsgroup, especially a technical one.
If this question arises it is because people need that isn't it?


I've never needed it, and if I did I'd probably change languages.
(Although the idea of a variadic with the first argument declaring
type is neat...) But needs aren't really here or there when it comes
to topicality on this newsgroup. The topic is Standard C and/or
pre-Standard K&R C, and neither languages has any concept of function
overloading or polymorphism or inheritance or anything else of the
sort.

And, good job with curing yourself of top-posting! It's appreciated,
and makes people more likely to regard you as clueful.
Nov 13 '05 #14

This thread has been closed and replies have been disabled. Please start a new discussion.

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