在C ++中存储对数组的引用

Question

I have an array:

const int neoPixelCount = 40;
CRGB neoPixels[neoPixelCount];

And I have a Dancer , that needs to hold onto a reference of that array. It has an init method that looks like this:

// .h
class Dancer {
  public:
    CRGB neoPixels[];
    void init(CRGB neoPixels[]);
}

// .cpp
void Dancer::init(CRGB _neoPixels[]) {
  neoPixels = _neoPixels;
}

But when I call this, the compiler won't let me pass the reference to array.

dancer->init(neoPixels);

Which yields:

discobot/Dancer.cpp: In member function 'void Dancer::init(CRGB*)':

discobot/Dancer.cpp:14: error: incompatible types in assignment of 'CRGB*' to 'CRGB [0]'

What's the right syntax magic to make this work, and why?

Answer 1

You just need to change CRGB neoPixels[]; to CRGB* neoPixels; in the class member declaration, because you want to store a pointer (to the array) rather than a zero/unknown-length array.

Answer 2

If you want a reference to an array as a class member your should have something like that

class Dancer 
{
public:
    int (&neoPixels)[40]; // reference to an array of 40 elements
    Dancer(int (&neoPixels)[40]) : neoPixels(neoPixels) { }
};

The member neoPixels is a reference to an array of 40 elements (pardon the change to int , it was to do the checks in my machine).

Now since that's a reference it should be initialized in the constructor's initializer list.

To generalize the above idea, your class could be a template holding references to arrays of compile time known sizes.

template<size_t N>
class Dancer
{
    public:
    int (&neoPixels)[N]; // reference to an array of N elements
    Dancer(int (&neoPixels)[N]) : neoPixels(neoPixels) { }
};

Answer 3

I would suggest changing Dancer to:

class Dancer {
  public:
    CRGB* neoPixels;
    void init(CRGB neoPixels[]);
}