#include <X11/Xlib.h>
#include <cstdio>

int main()
{
    Display *display;
    Window rootwin;

    display = XOpenDisplay( NULL );
    if (!display) {
    	fprintf (stderr, "Cannot open display.\n");
    	return 1;
    }
    rootwin = DefaultRootWindow( display );
    XSelectInput( display, rootwin, SubstructureNotifyMask );

    XEvent event;

    while ( 1 ) {
        XNextEvent( display, &event );
        if ( event.type == CreateNotify ) {
            XCreateWindowEvent *createevent = (XCreateWindowEvent *)&event;
            printf( "%x\n", (unsigned int)(createevent->window) );
            fflush(stdout);
        }
    }

    return 0;
}