XSendEvent not working - c++

Question

I am trying to send an X event based on this example and the comments that followed it:
#include <X11/Xlib.h>
#include <X11/keysym.h>
#include <cstdio>
#include <iostream>
#include <string>
#include <unistd.h>
// #include <X11/extensions/XTest.h> // Uncomment to use XTestFakeKeyEvent()
// The key code to be sent.
// A full list of available codes can be found in /usr/include/X11/keysymdef.h
#define KEYCODE XK_Down
// Function to create an X11 keyboard event
// http://www.doctort.org/adam/nerd-notes/x11-fake-keypress-event.html
XKeyEvent createKeyEvent(Display *display, Window &win, Window &winRoot,
bool press, int keycode, int modifiers) {
XKeyEvent event;
event.display = display;
event.window = win;
event.root = winRoot;
event.subwindow = None;
event.time = CurrentTime;
event.x = 1;
event.y = 1;
event.x_root = 1;
event.y_root = 1;
event.same_screen = True;
event.keycode = XKeysymToKeycode(display, keycode);
event.state = modifiers;
if (press)
event.type = KeyPress;
else
event.type = KeyRelease;
return event;
}
int main() {
// Obtain the X11 display.
Display *display = XOpenDisplay(0);
if (display == NULL) return -1;
// Get the root window for the current display.
Window winRoot = XDefaultRootWindow(display);
// Find the window which has the current keyboard focus.
Window winFocus;
int revert;
XGetInputFocus(display, &winFocus, &revert);
// Send a fake key press event to the window.
XKeyEvent event =
createKeyEvent(display, winFocus, winRoot, true, KEYCODE, 0);
int res = XSendEvent(event.display, event.window, True, KeyPressMask,
(XEvent *)&event);
// int res =
// XTestFakeKeyEvent(event.display, event.keycode, True, CurrentTime);
std::cout << ((res != 0) ? std::string("Sent successfully")
: std::string("Sending failed")) << std::endl;
sleep(1);
if (XPending(display))
std::cout << "Got it!" << std::endl;
else
std::cout << "It's lost..." << std::endl;
// Done.
XCloseDisplay(display);
return 0;
}
Based on the output, the event gets sent OK and then gets lost, whether I use XSendEvent or XTestFakeKeyEvent (the commented out code). I am compiling the code with gcc 4.8.2 under Ubuntu 14.04. What is missing?

Answer 1

In order to receive events, an X11 application generally need to register an interest in them. This is done with the XSelectInput function:
XSelectInput(display, winFocus, KeyPressMask|KeyReleaseMask);
tells X11 that this client wants to receive key-press and key-release events associated with winFocus.