Call back method for shared library

arunka · 02-24-2006, 09:54 PM

Hi All,

i wrote an application which loads shared libraries at run time.
my question : is there any way a shared libray can call a method/funtion which is defines in the application?

Can we do this ?if yes how to do it.

Can any one help me?

thanks in adavnce
Arun.

paulsm4 · 02-25-2006, 01:10 AM

Sure - just use a "callback":

1. Your library function has a parameter that's a pointer to a function.

2. You program that calls the library function defines the actual function
(which is the "callback function

.

3. When your program calls the library function, it passes the callback.

4. Your library invokes the callback.

Examples of "callbacks" are numerous:

* signal handlers (in the Linux world)
* WinProc (in "classic Windows" programming)
* GTK+ event handlers
* etc etc

Try "man signal", for example.

Hko · 02-25-2006, 11:43 AM

The code of cpufreqd is a nice real-world example about how to load shared libraries as 'plugins' and let them register several call-back functions that get called from the main program.

As it is a complete program, it may look a bit tedious to dive into, but the code is quite clean IMHO, and not too big.