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For a project, I need to store an array of structures in PROGMEM. Array MessageTable[] will be composed of about ten struct InMessage elements. InMessage looks sort of like this:

struct AvcInMessage {
  MessageHandler  msgHandler;
  byte            dataSize;
  byte            data[8];
  char            description[20];
};

MessageHandler is not a data type... yet. I'm not really sure what data type to use. I want to be able to pick a message from the table and then call MessageTable[x].msgHandler() if that makes sense. I'm almost positive that this involves a pointer. Does someone here have an idea about what I'm looking for?

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  • It might be I'm misunderstanding, but it looks like you want to store in PROGMEM an array of structs containing a reference to an object... That looks a little overkill: do you need to have different message handlers for each item in the array? – Roberto Lo Giacco Dec 10 '18 at 2:04
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typedef void (*MessageHandler)(void);   // def messagehandler as pointer to func

struct AvcInMessage {
  MessageHandler  msgHandler;
  byte            dataSize;
  byte            data[8];
  char            description[20];
} InMessage[] = {
   {
      function1, <datasize>, {<byte0>, <byte1>, ..., }, "DescriptionHere"
   },
   // etc, for however many elements InMessage[] has.
};

The typedef defines a "pointer to function of void returning void" - fix up the argument count and types, and the return type to your needs. We're assuming each element's function has the same kind of arglist and return type. (Update: Sorry for the bug in my first iteration).

The next statement both defines the array of struct and initializes N of them. Provide an element count in the [] if you don't have a full set of initializers at compile time.

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  • I think I understand what you mean, but it doesn't compile. I get expected unqualified-id before ')' token. – Bo Thompson Dec 10 '18 at 2:24
  • 2
    should that be typedef void (*MessageHandler)(void); – Jaromanda X Dec 10 '18 at 4:26
  • @JaromandaX has it (thank you!). I've updated my answer. – JRobert Dec 10 '18 at 13:06
  • Confirming that the revised code works. Thank you very much, both. – Bo Thompson Dec 13 '18 at 18:20

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