Access Fpp constant array in cpp

[zimri-leisher]

You can access numeric FPP constants in CPP like so:

module Test {
constant X = 123
}

in cpp:

Test::X

However, I can't seem to find any code generated for a constant like this:

constant ARR = [1, 2, 3]

Am I missing something? Or is it not possible to access Fpp constant arrays in CPP?

[bocchino]

It's currently not possible. This was a design decision from the early days of FPP, when we didn't have direct C++ code generation for arrays and structs. Now it seems we could support array and struct constants in C++.

[Kronos3]

It's still a bit tricky since we'd need to codegen C++ definitions for anonymous array/struct types. There might be an easier way if we somehow type constants with a concrete FPP type.

[bocchino]

Yes, we might have to generate a C++ array or struct type with a synthetic name (say some code gen prefix plus the name of the constant) to represent the type of the constant. I added this feature request to nasa/fpp#269.

[bocchino]

Yes, we might have to generate a C++ array or struct type with a synthetic name

Actually I think it's better to use a C++ template, and let the compiler manage the code gen. That way we avoid what we were doing before with strings, where n constants with the same anonymous array or struct type would cause n different classes to be generated.

[zimri-leisher]

yes, an FppArrayConstant<int size, typename E> type would probably suffice. Maybe you could even use one of those fancy new data types you added?

[bocchino]

Yes, that's a good idea for arrays. For structs, maybe we could use a constexpr C-style struct. Something like this:

#include <cstdint>

using Type_of_s = struct { uint32_t x; float y; };

extern const Type_of_s s;

constexpr Type_of_s s = { 1, 2.0 };