Pointer to array - initialize element

Question

I have a class Pixel and a class Image with a function used to update a pixel line. I want to initialize the pixel line. My problem is to initialize the array. Actually I have this :

bool UpdateLine(Pixel line[], int nb)
{
    bool noError = true;
    line = new Pixel[nb];
    for (int r = 0; r < nb; r++)
    {
        line[r] = new Pixel(); // -> line causing troubles

        // do some stuff with my pixel
        [...]
    }
    return noError;
}

When I try this I have :

no viable overloaded '='

How can I initialize each elements for my array ?

Answer 1

You actually have two problems.

The first, regarding your error, is because new Pixel() results in a pointer to a Pixel object. In C++ you don't need new to create objects (do you come from a Java or C# background perhaps?). The initial allocation of the array creates the objects for you.

The second problem is that you assign to the pointer variable line, but line is a local variable inside the function. All modification to it will be lost once the function returns, and you will have a memory leak. You need to pass line by reference.

---

In the future when dealing with collections of a single type of data, I suggest you use std::vector instead. You still need to pass the vector by reference though, if you want to add elements to it.

Answer 2

    line[r] = new Pixel(); // -> line causing troubles

line[r] is a Pixel object, not a pointer, so you can't assign a pointer to it.

Why aren't you using a std::vector?