Get an X window ID

[eberrocal at laurel.datsi.fi.upm.es]

My problem is that I need to know the ID of an X window.

I have a program that lunch other program with the typical fork() and
after execl().

I have the ID of the process but I need the ID of the window because I
need to send X events to this window.

There are any form to get the window ID of a program (of what I have his
process ID) ??:

Thanks for your time.

Edu.