pset4/filter: What is being instantiated with RGBTRIPLE(*image)[width]

Question

I'm struggling to get my head around what is being instantiated here with (*image) (and what to do with it) in this line:

RGBTRIPLE(*image)[width] = calloc(height, width * sizeof(RGBTRIPLE));

I understand what is being assigned - a chunk of memory as an array of RGBTRIPLEs of width width*sizeof(RGBTRIPLE), but what is (*image) doing and how do I use it? I think it's a pointer to the array; in which case am I using it correctly when I pass it to further functions:

void avg(RGBTRIPLE image[])
{
    printf("b image: %p\n", image);
}

// Blur image
void blur(int height, int width, RGBTRIPLE image[height][width])
{
    printf("a image: %p\n", image);

    avg(*image); // defereference image

    return;
}

>> a image: 0x7f4450729010
>> b image: 0x7f4450729010

Is this the correct way to use *image (I was to pass a reference to the original image array to my function avg(), not a copy of the array)?

Answer 1

You are right in saying that image points to the array. However:

void avg(RGBTRIPLE image[])

is the same as:

void avg(RGBTRIPLE *image)

so, you're only printing the address pointed to by image[0][0] with:

printf("b image: %p\n", image);

I'm not sure of what you're trying to do by passing the image array to the avg function though.