Arduino C++ Dereference a #define or const int?

Question

I'm very rusty on my C++ so forgive me if this isn't a question about dereferencing at all. But I think that's the right terminology.

I'm putting together an Arduino sketch to send out raw infrared signals to emulate IR controllers.

To achieve this I'm sending a JSON string that references the signal defined in a header file that I'm including. I'm thinking of having a separate file for each controller and I want to use a #define statement in each header to ensure that I get good separation of each signal name. Sort of a roll my own namespace if you will.

So in the header I have this signal for the power button on a remote:

#include <stdint.h>
#include <Arduino.h>

#define AKB73575431_DATA_LEN 69
String AKB73575431_mfr = "LG";
uint16_t AKB73575431_power [AKB73575431_DATA_LEN] = {
  4400,4600,550,600,500,600,550,1650,550,1700,
  550,600,500,1700,550,600,550,600,500,600,
  550,550,550,1700,550,1650,550,600,550,1700,
  500,650,500,600,500,600,550,1700,550,1650,
  600,1650,550,1700,550,600,500,600,550,600,
  500,1700,550,600,550,550,550,600,500,600,
  500,1700,600,1650,550,1700,550,1000
};

Some of you might recognise this data format as cribbed straight from the tutorials on IRLib2.

I want to send a JSON string:

{"cmd": "txIRraw", "key": "AKB73575431_power"}

My question is can I parse the string in the "key" value and use the substring:

AKB73575431

to construct a reference to the define:

#define AKB73575431_DATA_LEN 69

Failing that, is it possible to change the define to a global int and dereference it instead?

I've been Googling dereferencing variables in C++ but keep getting pages on pointers. What I want to do is construct the variable or #define name from a string and then use that.

Is this possible and if so, can someone give me an example?

Many thanks

Kali

Answer 1

If I'm understanding your question correctly, you are trying to see if you can use the string "AKB73575431" , to create a variable with the same name AKB73575431 , and assign the value of AKB_LEN to it.

The quick answer would be no. You can't create a variable name based on values from another string.

There are two different approach you could use to get to similar effect(I guess).

---

First you can utilize macros.

You could do something the other way around. Say if you want to create multiple variable with prefix AKB_ , such as AKB_len , AKB_power , AKB_mfr . You can do that with macro:

#define create(NAME, VALUE) decltype(VALUE) AKB_##NAME{VALUE}

So you can use it like:

create(LEN, 10); // create a variable called `AKB_LEN`, and has the value of 10

or:

string s = "abc";
create(S, s); // create a variable called `AKB_S`, and has the type string and value "abc"

However, I would not recommend this. It's hard to get the variable name you created, as they are hidden under macros. And if you have another remote, with a different name, you would need to create a whole new macro function, to get them to work.

---

The second way is through OOP. You would create a Remote class, and the Remote might have different members such as name, mfr, and power:

struct Remote
{
    std::string name;
    std::string mfr;
    std::vector<int> power;
}

And then you can create Remote like:

Remote AKB{"AKB", AKB_mfr, {std::being(AKB_power}, std::end(AKB_power)};

Then you can access data of it with things like AKB.mfr , AKB.power

---

Furthermore, you could also make the Remote class without the name member, and store remotes in a map container:

struct Remote
{
    std::string mfr;
    std::vector<int> power;
}

Then you can create a map like:

std::map<std::string, Remote> Remotes;

And add new remotes to the map like:

Remotes.emplace("AKB", Remote{AKB_mfr, {std::begin(AKB_power), std::end(AKB_power)}});

Now if you want to access a remote called "AKB" from the map, you can do things like:

Remotes["AKB"].mfr