callback functions

[prashant.khade1623@gmail.com]

What are callback function ?

how are they implemented and where they are useful ?

what are the advantages of function pointer ?

[Ian Collins]

Re: callback functions

prashant.khade1 623@gmail.com wrote:

What are callback function ?
>
how are they implemented and where they are useful ?
>
what are the advantages of function pointer ?

Have you looked for the answers?

--
Ian Collins.

[prashant.khade1623@gmail.com]

Re: callback functions

On Apr 11, 1:41 pm, Ian Collins <ian-n...@hotmail.co mwrote:

prashant.khade1 ...@gmail.com wrote:

What are callback function ?

>

how are they implemented and where they are useful ?

>

what are the advantages of function pointer ?

>
Have you looked for the answers?
>
--
Ian Collins.

I have googled.. but I couldnt find something which I can understand

[Chris Thomasson]

Re: callback functions

<prashant.khade 1623@gmail.comw rote in message
news:faf90c22-c153-4367-849b-d1610dc6606f@w4 g2000prd.google groups.com...
On Apr 11, 1:41 pm, Ian Collins <ian-n...@hotmail.co mwrote:

prashant.khade1 ...@gmail.com wrote:

What are callback function ?

how are they implemented and where they are useful ?

what are the advantages of function pointer ?

Have you looked for the answers?

--
Ian Collins.

I have googled.. but I couldnt find something which I can understand

Inform your professor immediately. Give him an example that you don't
understand... See what his reaction is... Who knows, she/he may try to help
you understand...

[Ian Collins]

Re: callback functions

Richard Heathfield wrote:

prashant.khade1 623@gmail.com said:
>

>What are callback function ?

>
Functions that you tell other functions about.
>

Doing homework now are we?

--
Ian Collins.

[Richard Heathfield]

Re: callback functions

Ian Collins said:

Richard Heathfield wrote:

>prashant.khade1 623@gmail.com said:
>>

>>What are callback function ?

>>
>Functions that you tell other functions about.
>>

Doing homework now are we?

Hmmm? Oh, er, maybe. Good point.




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[Jack Klein]

Re: callback functions

On Fri, 11 Apr 2008 08:49:31 +0000, Richard Heathfield
<rjh@see.sig.in validwrote in comp.lang.c:

prashant.khade1 623@gmail.com said:
>

What are callback function ?

>
Functions that you tell other functions about.
>

how are they implemented

>
The function is implemented in the usual way - i.e. it's a function. The
callback bit is done via a pointer to the function - you pass such a
function pointer to the function that you want to call you back.

What you describe above is the most common usage of callback
functions, I suppose, but not the only one.

In some cases the overhead of passing an extra function pointer object
to every call is excessively burdensome. In other cases, it is not
even always possible, for example in a kernel, although that takes us
somewhat outside the realm of standard, portable code.

In some cases I have provided packages which contain an external
declaration like this:

extern void (*Fatal_Error_H andler)(void);

....with the user documentation indicating that their program must
define such a pointer and assign either NULL or a real function to put
the system into a fail safe state and not actually return.

This usage can save quite a bit of overhead if there are only one or a
few specific callbacks needed, and they are only for extreme cases.

--
Jack Klein
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[Richard Heathfield]

Re: callback functions

Jack Klein said:

<snip>

>
In some cases the overhead of passing an extra function pointer object
to every call is excessively burdensome. In other cases, it is not
even always possible, for example in a kernel, although that takes us
somewhat outside the realm of standard, portable code.
>
In some cases I have provided packages which contain an external
declaration like this:
>
extern void (*Fatal_Error_H andler)(void);
>
...with the user documentation indicating that their program must
define such a pointer and assign either NULL or a real function to put
the system into a fail safe state and not actually return.

Where every object in a container is likely to use the same callback (e.g.
linked-list- or tree-walking), I have a pointer in the container itself
rather than in any of its nodes, and set that up with a call to something
like:

int list_set_iterat or(list *lst, iterator *fn);

Of course, the effect is the same.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999