is there a way to declare a ranged based array in c++ arduino?

Question

is there a way to declare a range based array in c++ arduino for example instad of writing

const int array[] = {2,3,4,5,6};

why isn't it possible to declare an array like this?

const int array[] = {2:6};

Answer 1

I assume that you are not using the Arduino STL, so you could create a simple array wrapping class template, similar to std::array , that takes two template parameters: The type, T , and the size, N .

Example:

template<class T, size_t N>
struct array {
    // misc typedef's:
    using value_type = T;
    using const_pointer = const value_type*;
    using pointer = value_type*;
    using const_iterator = const value_type*;
    using iterator = value_type*;

    size_t size() const { return N; } // the fixed size of the array

    // subscripting:
    const T& operator[](size_t idx) const { return data[idx]; }
    T& operator[](size_t idx) { return data[idx]; }

    // implicit conversions when passed to functions:
    operator const_pointer () const { return data; }
    operator pointer () { return data; }

    // iterator support:   
    const_iterator cbegin() const { return data; }
    const_iterator cend() const { return data + N; }
    const_iterator begin() const { return cbegin(); }
    const_iterator end() const { return cend(); }
    iterator begin() { return data; }
    iterator end() { return data + N; }

    T data[N]; // the actual array
};

You could then create a small helper function to create arrays and fill them with a range of values like in your question:

template<class T, T min, T max>
array<T, max - min + 1> make_array_min_max() {
    array<T, max - min + 1> rv;
    for(T i = min; i <= max; ++i) rv[i - min] = i;
    return rv;
}

The creation would just be slightly different, but you could then use it pretty much like you use a normal array.

void func(const int* a, size_t s) {                   // C-style interface
    for(size_t i = 0; i < s; ++i)
        std::cout << a[i] << ' ';
    std::cout << '\n';
}

int main() {
    const auto arr = make_array_min_max<int, 2, 6>(); // create the range you want

    func(arr, arr.size());         // implicit conversion to `const int*` for `arr`
    
    for(auto v : arr)                                 // range-based for loop
        std::cout << v << ' ';
    std::cout << '\n';

    for(size_t i = 0; i < arr.size(); ++i)            // classing loop
        std::cout << arr[i] << ' ';
    std::cout << '\n';
}

Output:

2 3 4 5 6 
2 3 4 5 6 
2 3 4 5 6