typedef enum statement confusion.

This is a discussion on typedef enum statement confusion. within the C Programming forums, part of the General Programming Boards category; Hey all, thanks for the help. This should be fairly easy for someone who understands this syntax well. I am ...

  1. #1
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    typedef enum statement confusion.

    Hey all, thanks for the help. This should be fairly easy for someone who understands this syntax well. I am modifying some code for work, but ran into a little confusion with the statement below, cannot find what i need online. I understand typedef and enum alone, but the syntax here is throwing me off. Doesn't enum need a declaration of a variable name after it, before the list? And does typedef before enum cause each on to be an individual variable type? Either case does not make much sense. I just two statements of code with this syntax usage, but it appears much more so it is vital that I know what is going on. Thanks much.

    Code:
    typedef enum {
      CLK_PRESCALER_HSIDIV1   = (u8)0x00, /*!< High speed internal clock prescaler: 1 */
      CLK_PRESCALER_HSIDIV2   = (u8)0x08, /*!< High speed internal clock prescaler: 2 */
      CLK_PRESCALER_HSIDIV4   = (u8)0x10, /*!< High speed internal clock prescaler: 4 */
      CLK_PRESCALER_HSIDIV8   = (u8)0x18, /*!< High speed internal clock prescaler: 8 */
      CLK_PRESCALER_CPUDIV1   = (u8)0x80, /*!< CPU clock division factors 1 */
      CLK_PRESCALER_CPUDIV2   = (u8)0x81, /*!< CPU clock division factors 2 */
      CLK_PRESCALER_CPUDIV4   = (u8)0x82, /*!< CPU clock division factors 4 */
      CLK_PRESCALER_CPUDIV8   = (u8)0x83, /*!< CPU clock division factors 8 */
      CLK_PRESCALER_CPUDIV16  = (u8)0x84, /*!< CPU clock division factors 16 */
      CLK_PRESCALER_CPUDIV32  = (u8)0x85, /*!< CPU clock division factors 32 */
      CLK_PRESCALER_CPUDIV64  = (u8)0x86, /*!< CPU clock division factors 64 */
      CLK_PRESCALER_CPUDIV128 = (u8)0x87  /*!< CPU clock division factors 128 */
    } CLK_Prescaler_TypeDef;
    
    /**
       * @brief  SWIM Clock divider.
       */
    typedef enum {
      CLK_SWIMDIVIDER_2 = (u8)0x00, /*!< SWIM clock is divided by 2 */
      CLK_SWIMDIVIDER_OTHER = (u8)0x01 /*!< SWIM clock is not divided by 2 */
    }CLK_SWIMDivider_TypeDef;

  2. #2
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    Quote Originally Posted by Daniel.Blesener
    Doesn't enum need a declaration of a variable name after it, before the list?
    I think you mean the enumeration name rather than a variable name. The answer is no: the enumeration is anonymous, but...

    Quote Originally Posted by Daniel.Blesener
    does typedef before enum cause each on to be an individual variable type?
    ... the typedef gives the enumeration a name, e.g., CLK_Prescaler_TypeDef. So yes, it is a type name.
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    Quote Originally Posted by Daniel.Blesener View Post
    Hey all, thanks for the help. This should be fairly easy for someone who understands this syntax well. I am modifying some code for work, but ran into a little confusion with the statement below, cannot find what i need online. I understand typedef and enum alone, but the syntax here is throwing me off. Doesn't enum need a declaration of a variable name after it, before the list?
    That's technically referred to as a tag and is optional.
    Quote Originally Posted by Daniel.Blesener View Post
    And does typedef before enum cause each on to be an individual variable type?
    Yep!

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    Thanks for the quick replies! I still do not understand what
    Code:
    CLK_Prescaler_TypeDef;
    means though? Does it need to be there? All the statements like this have something at the end similar.
    Why does the statement have
    Code:
    CLK_Prescaler_TypeDef;
    written outside of the parenthesis? Thanks!

    Last edited by Daniel.Blesener; 06-19-2012 at 12:18 PM.

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    Quote Originally Posted by Daniel.Blesener View Post
    Thanks for the quick replies! I still do not understand what
    Code:
    CLK_Prescaler_TypeDef;
    means though?
    It's just a name for the new type you have created. Consider this:
    Code:
    typedef enum {small, medium, large} size;  /* now size is a new name for "enum {small, medium, large}" */
    size dimension;  /* makes dimension a variable of type size aka enum {small, medium, large} */
    Last edited by itCbitC; 06-19-2012 at 01:59 PM.

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