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| From | James Kuyper <jameskuyper@verizon.net> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Function factories |
| Date | 2012-08-22 13:01 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <50351056.10908@verizon.net> (permalink) |
| References | <k10rgf$oep$1@speranza.aioe.org> <pan.2012.08.21.20.55.41.481000@nowhere.com> <k131pp$8gi$1@speranza.aioe.org> |
On 08/22/2012 12:36 PM, Edward Rutherford wrote:
> Nobody wrote:
>> On Tue, 21 Aug 2012 20:36:31 +0000, Edward Rutherford wrote:
...
>>> The idea is that adder_factor(42) should be a function that adds 42 to
>>> whatever it gets passed.
>>>
>>> What's the right way of doing this in C? How can I get closures or
>>> something similar in C?
>>
>> typedef struct foo {
>> int (*func)(const struct foo *, int); int param;
>> } *foo;
>>
>> static int adder(const struct foo *closure, int x) {
>> return closure->param + x;
>> }
>>
>> foo adder_factory(int x)
>> {
>> foo p = malloc(sizeof(*p));
>> p->func = adder;
>> p->param = x;
>> return p;
>> }
>>
>> #define call_foo(f, x) ((f)->func((f), (x))
>
> Thanks for the suggestion. Unfortunately I need an actual function, not a
> macro, to be able to pass as a comparator function to qsort.
>
> Guess I just have to communicate what I need through a global variable?
That's one alternative. However, you can avoid creating a global, with
all of the attendant problems. When used correctly, qsort() never calls
the comparison function with null pointers. You can take advantage of
that fact by making x a static variable local to the comparison
function, and if the first argument to that function is a null pointer,
interpret the second argument as a pointer to a new value for x.
> It would be nice if qsort took an extra "void *data" parameter, like
> functions in Glib (where it's called a gpointer of course)...
Yes. It's a well-known problem with all of the original C standard
library's callback functions. I think C11 has introduced some new
callbacks, but I haven't had time to learn much about them.
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Function factories Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2012-08-21 20:36 +0000
Re: Function factories Nobody <nobody@nowhere.com> - 2012-08-21 21:55 +0100
Re: Function factories Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2012-08-22 16:36 +0000
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-22 13:01 -0400
Re: Function factories Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2012-08-22 18:33 +0000
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-22 22:26 -0400
Re: Function factories David Brown <david@westcontrol.removethisbit.com> - 2012-08-22 08:34 +0200
Re: Function factories Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-08-22 01:52 -0700
Re: Function factories David Brown <david@westcontrol.removethisbit.com> - 2012-08-22 11:34 +0200
Re: Function factories Gareth Owen <gwowen@gmail.com> - 2012-08-24 17:30 +0100
Re: Function factories Gareth Owen <gwowen@gmail.com> - 2012-08-24 17:29 +0100
Re: Function factories jacob navia <jacob@spamsink.net> - 2012-08-22 12:32 +0200
Re: Function factories tom st denis <tom@iahu.ca> - 2012-08-22 07:40 -0700
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-22 11:05 -0400
Re: Function factories jacob navia <jacob@spamsink.net> - 2012-08-23 11:08 +0200
Re: Function factories Chicken McNuggets <chicken@mcnuggets.com> - 2012-08-23 13:27 +0100
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-23 11:13 -0400
Re: Function factories "Heinrich Wolf" <invalid@invalid.invalid> - 2012-08-23 18:18 +0200
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-23 12:40 -0400
Re: Function factories Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2012-08-23 09:29 -0700
Re: Function factories jacob navia <jacob@spamsink.net> - 2012-08-23 18:44 +0200
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-23 12:46 -0400
Re: Function factories Chicken McNuggets <chicken@mcnuggets.com> - 2012-08-23 18:02 +0100
Re: Function factories jacob navia <jacob@spamsink.net> - 2012-08-23 19:24 +0200
Re: Function factories eq mail <eq.mail.id@gmail.com> - 2012-08-23 18:07 -0700
Re: Function factories Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-23 21:30 -0400
Re: Function factories eq mail <eq.mail.id@gmail.com> - 2012-08-23 21:46 -0700
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-23 13:35 -0400
Re: Function factories jacob navia <jacob@spamsink.net> - 2012-08-23 20:13 +0200
Re: Function factories eq mail <eq.mail.id@gmail.com> - 2012-08-23 17:57 -0700
Re: Function factories Andrew Cooper <amc96@cam.ac.uk> - 2012-08-25 02:35 +0100
Re: Function factories Melzzzzz <mel@zzzzz.invalid> - 2012-08-23 21:21 +0200
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-23 15:36 -0400
Re: Function factories Melzzzzz <mel@zzzzz.invalid> - 2012-08-23 22:09 +0200
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-23 16:20 -0400
Re: Function factories Melzzzzz <mel@zzzzz.com> - 2012-08-23 22:33 +0200
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-23 17:07 -0400
Re: Function factories Keith Thompson <kst-u@mib.org> - 2012-08-23 14:51 -0700
Re: Function factories Melzzzzz <mel@zzzzz.com> - 2012-08-24 00:09 +0200
Re: Function factories James Kuyper <jameskuyper@verizon.net> - 2012-08-23 19:01 -0400
Re: Function factories Keith Thompson <kst-u@mib.org> - 2012-08-23 16:31 -0700
Re: Function factories Melzzzzz <mel@zzzzz.com> - 2012-08-24 18:31 +0200
Re: Function factories Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-08-24 02:37 -0700
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