Device detection C++

[statesman]

Hi,
I wanted to know something about callback functions.
Glut provides default function for identifying mouse movement

void glutMotionFunc(void (*func) (int x,int y));
void glutPassiveMotionFunc(void (*func) (int x, int y));

How is it created?There must be some code for creating this.
I mean how can I make such function for any device(moving device)?

I tried to find the definition of these functions but could not find.

Thanks.