About the concept of the callback function

[mr924352@cs.nthu.edu.tw]

Hello everybody:

I trace the gdb source code now.

In the gdb source code,there use many callback function.

I don't understand why it uses callback.

Now, i know how to implement the callback function.

But, i still don't know why it must use the callback. 

Anyone can tell me where is the document about the concept of the callback

function that i can get.

                          Thank a lot!!!