Question

I have several drivers using a resource in my code, of which only one can be defined.
eg if I have the following defines: USB_HID, USB_SERIAL, USB_STORAGE.
and I want to test that only one is defined, is there a simple way to do this?
Currently I am doing it this way:

#ifdef USB_HID
  #ifdef USB_INUSE
    #error "Can only have one USB device"
  #else
    #define USB_INUSE
  #endif
#endif

#ifdef USB_SERIAL
  #ifdef USB_INUSE
    #error "Can only have one USB device"
  #else
    #define USB_INUSE
  #endif
#endif

…
with one of these blocks for each USB_XXX driver.
Is there more elegant way of doing this?

Answer 1

#if defined(USB_HID) + defined(USB_SERIAL) + defined(USB_STORAGE) != 1
#error Define exactly one of USB_HID, USB_SERIAL, USB_STORAGE
#endif