Set window focus on desired window ID.

raisefocus.c

/* Set window focus on desired window ID.
   gcc -Wall -lX11 raisefocus.c
*/
#include <X11/Xlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <libgen.h>

// This routine is taken directly from wmctr:main.c
static int client_msg(Display *disp, Window win, char *msg, /* {{{ */
		      unsigned long data0, unsigned long data1,
		      unsigned long data2, unsigned long data3,
		      unsigned long data4) {
	XEvent event;
	long mask = SubstructureRedirectMask | SubstructureNotifyMask;

	event.xclient.type = ClientMessage;
	event.xclient.serial = 0;
	event.xclient.send_event = True;
	event.xclient.message_type = XInternAtom(disp, msg, False);
	event.xclient.window = win;
	event.xclient.format = 32;
	event.xclient.data.l[0] = data0;
	event.xclient.data.l[1] = data1;
	event.xclient.data.l[2] = data2;
	event.xclient.data.l[3] = data3;
	event.xclient.data.l[4] = data4;

	if (XSendEvent(disp, DefaultRootWindow(disp), False, mask, &event)) {
		return EXIT_SUCCESS;
	}
	else {
		fprintf(stderr, "Cannot send %s event.\n", msg);
		return EXIT_FAILURE;
	}
}/*}}}*/

int main(int argc, char *argv[]) {

	if(argc < 2) {
		fprintf(stderr, "Usage: %s <window id>\n",
			basename(argv[0]));
		return(EXIT_SUCCESS);
	}

	Window winid = strtol(argv[1], NULL, 0);

	printf("Window id: 0x%lx\n", winid);

	Display *disp = XOpenDisplay(NULL);

	if (! disp) {
		fputs("Cannot open display.\n", stderr);
		return(EXIT_FAILURE);
	}

	int r = client_msg(disp, 
			   winid, 
			   "_NET_ACTIVE_WINDOW",
			   0, 0, 0, 0, 0);

	XCloseDisplay(disp);

	return(r);
}