Callback function?

[Pradeep]

Hi all,
Can any one explain me what is callback function....
I have written some code after reading some tutorials from internet...
But I am not sure is it a right way to write a call back function...
I have mentioned my doubts in code comments.
My code is...

void myfun_callback(void(*fp)(char*)) //is this function is a call
back?
{
(*fp)("Pradeep Kumar");
}

void A(char *msg) //function A,called by myfun_callback
{
cout<<"Function A: "<<msg<<endl;
}

void B(char *msg) //function A,called by myfun_callback
{
cout<<"Function B: "<<msg<<endl;
}

int main()
{
void(*fp)(char*); //function pointer
fp=A; //giving address of function A
myfun(fp); //right way to call the callback function?
fp=B; //giving address of function B
myfun(fp); //right way to call the callback function?
return 0;
}

ur help will be appreciated..
Thank u in advance

Regards
Pradeep Kumar Basrani

[Victor Bazarov]

Pradeep wrote:

Can any one explain me what is callback function....

A callback function is a function pointer to which is supplied to (and
stored by) the system (whatever the system is) to be called at some
indetermined time, generally speaking. Sometimes the time at which the
callback is called is a bit clearer defined, but it doesn't mean the
path to the callback is (or can be) determined.

I have written some code after reading some tutorials from internet...
But I am not sure is it a right way to write a call back function...
I have mentioned my doubts in code comments.
My code is...

void myfun_callback(void(*fp)(char*)) //is this function is a call
back?

No. This function is not a callback _unless_ you give it to some
other function to be called.

{
(*fp)("Pradeep Kumar");
}

void A(char *msg) //function A,called by myfun_callback

This function is most likely a callback.

{
cout<<"Function A: "<<msg<<endl;
}

void B(char *msg) //function A,called by myfun_callback

This is another function that is likely a callback.

{
cout<<"Function B: "<<msg<<endl;
}

int main()
{
void(*fp)(char*); //function pointer
fp=A; //giving address of function A
myfun(fp); //right way to call the callback function?

It's a way to call a function that will *in turn* call the
callback you supply to it.

fp=B; //giving address of function B
myfun(fp); //right way to call the callback function?
return 0;
}

ur help will be appreciated..
Thank u in advance

Try to use English here and avoid chatroomisms.

V
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[Ehud Shapira]

A callback function is a function in your code that is called by
something outside of your control; it could be the operating system,
or it could be a 3rd party library you are using.

This typically means you first give out a pointer to that function to
the external caller.

Other than that, it's a function like any other, but of course, it
should work according to what the external caller expects.