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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?

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3 Answers 3

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

Nice solution. I probably would have ended up with a nasty mash of && || operators.
Really nice, +1. @Mike Weller: me too :)
Legend answer, I was awash in operators before I saw this.
0

Yes, use the define operator such as:

#if defined (USB_HID) && defined (USB_INUSE)

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Comments

0

Why not #elif ?

#if defined(USB_HID)
   #define USB_INUSE
#elif defined(USB_SERIAL)
   #define USB_INUSE
#endif
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