C and xlib: Crash in XPending() in a very simple program

I'm a beginner with xlib. I tried to program an Xwindow application using select() based on this example: how to quit the blocking of xlib's XNextEvent.

But the code mentioned above crashes in the XPending function. So I tried to isolate the problem and on my system even this from my point of view very simple example crashes on line 28. Due to several tests I assume is crashes internally by calling XFlush(). At the line marked with "// <- CRASH" I think XPending should return 0. Is that correct?

#include <stdio.h>#include <stdlib.h>#include <X11/Xlib.h>#include <X11/Xutil.h>Display *dis;Window win;int x11_fd;fd_set in_fds;struct timeval tv;XKeyEvent ev;int main() {    dis = XOpenDisplay(NULL);    win = XCreateSimpleWindow(dis, RootWindow(dis, 0), 1, 1, 256, 256, \        0, BlackPixel (dis, 0), BlackPixel(dis, 0));    XSelectInput(dis, win,         KeyPressMask | KeyReleaseMask );    XMapWindow(dis, win);    XFlush(dis);    printf("Xpending: %d\n",XPending(dis));      printf("Xpending: %d\n",XPending(dis));      XPeekEvent(dis, (XEvent*) &ev);    printf("type: %d button: 0x%X state: 0x%x\n",ev.type, ev.keycode, ev.state);      int j = XPending(dis); // <- CRASH    printf("XPending: %d\n",j);      return 0;}

Is this a bug or have I mistaken a major concept in xlib?