Determine number of input devices
#include <X11/extensions/dmxext.h>
Bool DMXGetInputCount(Display *dpy, int *input_count);
DMXGetInputCount() returns the number of input devices connected to the Xdmx(1) server in input_count. This number is the same as that returned by XListInputDevices(3), but is available even when the XInput extension is not supported.
DMXGetInputCount() returns True unless there is a protocol error.