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Re: How to transmit the value of an enumeration

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Il 24/10/2018 19:48, Joe Chisolm ha scritto:
 > On Wed, 24 Oct 2018 13:18:15 +0200, pozz wrote:
 >
 >> enum type_t {
 >>     TYPE_1,
 >>     TYPE_2,
 >>     ...
 >>     TYPE_100,
 >> }
 >>
 >> void tx_byte(unsigned char c);
 >>
 >> enum type_t t;
 >> ...
 >> tx_byte((unsigned char)t);
 >>
 >>
 >> If the maximum value in the enumeration is lower than 256, you can cast
 >> to (unsigned char) and transmit it as a byte.
 >>
 >>
 >> However the receiver must have the same enumeration.  The transmitter
 >> and the receiver must agreed on *the exact values* of the enumeration.
 >>
 >> What happens if the developer of the transmitter thinks that it is
 >> better to swap some values during a future release?  The enumeration
 >> isn't used only for transmission, it is also used for general logic of
 >> the software.
 >>
 >> Until now I didn't found a good solution.  I only write some comments
 >> before the enumeration declaration:
 >>
 >> /* WARNING!! DON'T CHANGE THE ORDER OF THE VALUES INSIDE ENUMERATION
 >>    * They are also used in the transmission */
 >>
 >> I sometimes prefer explicit the value transmitted:
 >>
 >> if (t == TYPE_1) tx_byte(0);
 >> if (t == TYPE_2) tx_byte(1);
 >> ...
 >>
 >>
 >> What is your strategy?
 >
 > Your protocol document defines what is sent on the communications 
channel.
 > In your code you may have:
 >   enum type_t {
 >      TYPE_2,
 >      TYPE_1,
 >      ...
 >      TYPE_100
 >   }
 >
 > But in your protocol handler you have
 >   enum protocol_type_t {
 >      PTYPE_1,
 >      PTYPE_2,
 >      ...
 >      PTYPE_100
 >   }
 > switch(t) {
 > case TYPE_1:
 >    tx_byte(PTYPE_1);
 >
 > .....
 >
 > You convert your internal type_t to the external protocol protocol_type_t
 > and protocol_type_t always (well should always) matches the spec.

Yes, it seems *THE* best solution in order to avoid problems.  Even if 
it is tedious, because you have two enumerations instead of one and you 
have a long piece of translation code that is silly.

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Thread

How to transmit the value of an enumeration pozz <pozzugno@gmail.com> - 2018-10-24 13:18 +0200
  Re: How to transmit the value of an enumeration Jack <jack4747@gmail.com> - 2018-10-24 04:45 -0700
    Re: How to transmit the value of an enumeration pozz <pozzugno@gmail.com> - 2018-10-24 15:18 +0200
      Re: How to transmit the value of an enumeration David Brown <david.brown@hesbynett.no> - 2018-10-24 17:05 +0200
  Re: How to transmit the value of an enumeration David Brown <david.brown@hesbynett.no> - 2018-10-24 15:10 +0200
    Re: How to transmit the value of an enumeration pozz <pozzugno@gmail.com> - 2018-10-24 15:27 +0200
      Re: How to transmit the value of an enumeration David Brown <david.brown@hesbynett.no> - 2018-10-24 16:59 +0200
      Re: How to transmit the value of an enumeration Clifford Heath <no.spam@please.net> - 2018-10-25 08:57 +1100
  Re: How to transmit the value of an enumeration Joe Chisolm <jchisolm6@earthlink.net> - 2018-10-24 12:48 -0500
    Re: How to transmit the value of an enumeration pozz <pozzugno@gmail.com> - 2018-10-24 23:20 +0200
      Re: How to transmit the value of an enumeration Joe Chisolm <jchisolm6@earthlink.net> - 2018-10-24 22:21 -0500
    Re: How to transmit the value of an enumeration David Brown <david.brown@hesbynett.no> - 2018-10-25 09:31 +0200
      Re: How to transmit the value of an enumeration Rob Gaddi <rgaddi@highlandtechnology.invalid> - 2018-10-25 09:58 -0700
      Re: How to transmit the value of an enumeration Joe Chisolm <jchisolm6@earthlink.net> - 2018-10-25 18:38 -0500
        Re: How to transmit the value of an enumeration David Brown <david.brown@hesbynett.no> - 2018-10-26 09:24 +0200
  Re: How to transmit the value of an enumeration George Neuner <gneuner2@comcast.net> - 2018-10-24 15:19 -0400
  Re: How to transmit the value of an enumeration Les Cargill <lcargill99@comcast.com> - 2018-10-26 20:30 -0500

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