#include <stdio.h>
#include <string.h>
#include <locale.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/Xatom.h>

Display *dpy;
int screen;
Window root;
static Atom NetActiveWindow;

void 
focus(Window w){
    XEvent ev;
    ev.type = ClientMessage;
    ev.xclient.window = w;
    ev.xclient.message_type = NetActiveWindow;
    ev.xclient.format = 32;
    ev.xclient.data.l[0] = 0;
    ev.xclient.data.l[1] = CurrentTime;
    XSendEvent(dpy, root, False, (SubstructureNotifyMask|SubstructureRedirectMask), &ev);
}

int
main(int argc, char *argv[]) {
	dpy = XOpenDisplay(0);
	Window win;
	if(!dpy) {
		fprintf(stderr, "cannot open display\n");
		return 1;
	}
	screen = DefaultScreen(dpy);
	root = RootWindow(dpy, screen);
	NetActiveWindow = XInternAtom(dpy, "_NET_ACTIVE_WINDOW", False);
	sscanf(argv[1], "0x%x", &win);
	focus(win);

	XCloseDisplay(dpy);
	return 0;
}