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So I have this enum in a header file:

enum class ServoPort {PORT1 = 1, PORT2, PORT3, PORT4, PORT5, PORT6};

The trouble is that when I try to use it in the primary file (by doing MyClass::ServoPort::PORT1) I get a compile error:

exit status 1
expected unqualified-id before numeric constant

However, if I change the enum to be like so:

enum class ServoPort {PORT8 = 1, PORT9, PORT10, PORT11, PORT12, PORT13};

Then I do not get a compile error. What the heck? Can someone please shine some light on why this is happening?


  • Board: UNO R3
  • IDE: v1.8.5
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  • Please add which Arduino board and IDE version. Feb 12, 2019 at 20:54
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    @MikaelPatel done Feb 12, 2019 at 20:55
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    @MikaelPatel hmm, ok yeah I could see that being a problem if I was trying to do a #define PORT2 or something, but in this case I'm creating an enum that has a a member of that name. It seems to me that shouldn't cause a conflict? I'm from a Java background so maybe I don't know what I'm talking about... Feb 12, 2019 at 21:00
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    The defines are pre-processed symbols before compiling. Your definition gives an illegal syntax when replaced. PORT1 = 1, PORT2, becomes, 1 = 1, 2. Feb 12, 2019 at 21:03
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    @MikaelPatel I see, but shouldn't the preprocessor be smart enough to not do that? Feb 12, 2019 at 21:04

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