Assigning an element of a multidimensional array to a second array

Question

I have two arrays. The first array is a multidimensional array holding color values.

The 2nd array stores an active color from the 1st array. How can I assign an element from the multidimensional colors array to the 2nd EXCLUSIVE_COLOR array?

int colors[][3] = {
 { 255, 0, 0 }, 
 { 0, 255, 0 }, 
 { 0, 0, 255 }, 
 { 253, 7, 210 } 
};
int EXCLUSIVE_COLOR[3] = {0};

I tried the following but neither seemed to work:

 EXCLUSIVE_COLOR = { 
 colors[0][0], 
 colors[0][1], 
 colors[0][2]
 };
 // error: assigning to an array from an initializer list
 EXCLUSIVE_COLOR = colors[0];
 // error: invalid array assignment

• Juraj: what is the type of EXCLUSIVE_COLOR. you want a pointer to the array or a copy of the array?
• VerySeriousSoftwareEndeavours: Either one would work. EXCLUSIVE_COLOR is a 3 element int array.
• Juraj: int* EXCLUSIVE_COLOR = colors[0];. and then you can use EXCLUSIVE_COLOR[i]
• DataFiddler: Why do you use a two-dimensional array, if you have a one-dimensional array of Color elements in reality?

Answer 1

You can copy the array:

EXCLUSIVE_COLOR[0] = colors[0][0];
EXCLUSIVE_COLOR[1] = colors[0][1];
EXCLUSIVE_COLOR[2] = colors[0][2];

but this doesn't work in an initialization.

Alternatively, you can declare EXCLUSIVE_COLOR as a pointer to an array of 3 integers:

int (*EXCLUSIVE_COLOR)[3]; // pointer to array 3 of int

Then you can have this point to a row of the 2D array, either by assigning the pointer or in the initialization:

int (*EXCLUSIVE_COLOR)[3] = &colors[0]; // initialization
// Later in the program:
EXCLUSIVE_COLOR = &colors[1];

Note that when using this pointer, you will have to explicitly dereference it:

for (int i = 0; i < 3; i++)
 Serial.println((*EXCLUSIVE_COLOR)[i]);

Edit: As pointed out by Juraj in a comment, you can instead make EXCLUSIVE_COLOR a pointer to int. In this case you will make it point to the first element in the row you want:

int* EXCLUSIVE_COLOR = &colors[0][0];

One nice thing of this approach is that you can use the "decay to pointer" feature of the language to simplify the syntax:

int* EXCLUSIVE_COLOR = colors[0];
// Later
Serial.println(EXCLUSIVE_COLOR[i]);

• Juraj: a pointer to pointer? it doesn't look right
• Edgar Bonet: @Juraj: It's not a pointer to pointer, it's a pointer to an array.

Answer 2

Use arrays only where appropriate:

struct Color {byte r, g, b;};
const Color colors[] = {
 {0,255,0},
 {255,0,0}
};
const Color red = colors[1];

This works without const as well. But you should consider using const wherever possible.