X11 Shift + Tab keysym? - c

Question

How to detect Shift + Tab in Xlib? I'm able to match KeySym with XK_Tab, but it's not matching while holding shift to then check for ev->state & ShiftMask, so I'm kind of lost.
SOLUTION:
Thanks to Erdal Küçük's answer I was able to come up with the following function that detects Shift + Tab:
int detectShiftTab(XKeyEvent *xkey) {
return XLookupKeysym(xkey, 0) == XK_Tab && xkey->state & ShiftMask;
}

Answer 1

With a simple test, i realized that the ShiftMask is not reported on a KeyPress of the Shift key. Other than that, the ShiftMask is always set.
int main()
{
Display *dpy = XOpenDisplay(NULL);
Window win = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), 0, 0, 640, 480, 0, 0, 0);
XSetWindowAttributes attr = { .event_mask = (KeyPressMask | KeyReleaseMask) };
XChangeWindowAttributes(dpy, win, CWEventMask, &attr);
XMapWindow(dpy, win);
while (1) {
XEvent evt;
XNextEvent(dpy, &evt);
switch (evt.type) {
case KeyPress:
printf(
"key press: %s shiftmask: %d\n",
XKeysymToString(XLookupKeysym(&evt.xkey, 0)),
(evt.xkey.state & ShiftMask) == ShiftMask
);
break;
case KeyRelease:
printf(
"key release: %s shiftmask: %d\n",
XKeysymToString(XLookupKeysym(&evt.xkey, 0)),
(evt.xkey.state & ShiftMask) == ShiftMask
);
break;
}
}
return 0;
}
I get the following output (typing Shift + Tab):
key press: Shift_L shiftmask: 0
key press: Tab shiftmask: 1
key release: Tab shiftmask: 1
key release: Shift_L shiftmask: 1