Thread: Be confused with one function prototype

Here the function prototype manual goes,
Xlib Programming Manual: XSetErrorHandler

Code:

int (*XSetErrorHandler(handler))()
      int (*handler)(Display *, XErrorEvent *)

I'm confused with the first line

Code:

int (*XSetErrorHandler(handler))()

Most people use the function like that

Code:

int (*handler)(Display *, XErrorEvent *) = NULL;
int old(Display *d, XErrorEvent *e){...}
handler = XSetErrorHandler(old);
XSetErrorHandler(handler);

Others direct invoke the function

Code:

XSetErrorHandler(old);

I have no idea how the hell XSetErrorHandler works.

As I understood for XSetErrorHandler()
At first it in the bracket returns one function which returned pf integer value,and then invoke the function.
But it conflicts with

Code:

handler = XSetErrorHandler(old);

which obvisouly return function pointer.


what's the theory of the function?
how hell does function works?



I'm looking forware to the explanation.

Ching.