XtGetDisplays - retrieve a list of displays associated with an application
  context
#include <X11/Intrinsic.h>
void XtGetDisplays(XtAppContext app_context, Display
    ***dpy_return, Cardinal* num_dpy_return);
  - app_context
- Specifies the application context.
- dpy_return
- Returns a list of open X display connections in the specified application
      context.
- num_dpy_return
- Returns the count of open X display connections in dpy_return.
To free the list of displays, use XtFree.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface