#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <stdlib.h>
#include <stdio.h>

int main() {
    Display *display;
    Window window;
    XTextProperty text_prop_return;

    int revert;
    char *window_name;
    
  

    display = XOpenDisplay(NULL);
    if (display == NULL) {
        fprintf(stderr, "Cannot connect to X server %s\n", "simey:0");
        exit (-1);
    }

    XGetInputFocus(display, &window, &revert);
    int windowId = (unsigned)window;
    printf("id: %d\n", windowId);

    XGetWMName(display, window, &text_prop_return);
    printf("XGetWMName: %s, res_name:\n", text_prop_return.value);
    
    XFetchName(display, window, &window_name);
    printf("XFetchName: %s, res_name:\n", window_name);

    
    return 0;
}

sudo gcc -O w.c -o w -lX11