c++ - structure defined inside of class -

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• what weird colon-member (“ : ”) syntax in constructor? 12 answers

i'm newbie in c++, consider following snippet:

class myclass {   ...   struct entrykeybase   {      void setoperation(optype oper)      {         operation = oper;      }      optype getoperation() const      {         return operation;      }      virtual void serialize(std::ostream& os) const = 0;      protected:         optype operation;     };    struct protoentrykey: entrykeybase   {      // methods here       protoentrykey(uint8_t l4proto) : proto(l4proto)  // ???      {         operation = inserted;      }       protected:         uint8_t proto;   };    // here more structs defined...     public:     ...  }; 

what line marked ??? do? understand declare structure inheriting entrykeybase, whatever follows ':' don't understand, syntax mean? thanks!

it initialization list. assigns value of l4proto proto variable in struct protoentrykey.