Warning C6386 (with array, not fstream)

I was developing a Binary Class that uses three-state booleans to create an array with a clear delimiter (I didn’t want to use vector because I’m stuborn and the code I am using will be transported to an Arduino, which I do not know whether or not it has the std library). Here is the enumeration I used:

enum tribool { DELIM = -1, FALSE, TRUE };

I was developing the Copy Constructor (or Move Constructor, I forgot the difference) of the Binary Class and on "triboolList[i] = (const tribool)copyBinary.triboolList[i];" I was getting Warning C6386.

I looked at Microsoft Learn and I still didn’t understand the problem. I also looked at a stack overflow of this same issue; except the other person was having issues with this warning and std::fstream.

Image of the code because I was having issues with text formatting (Sorry in advance)

Edit: I should clarify that I haven’t found any runtime issues with the Copy Constructor yet, it’s just that the warning is concerning me a little bit

Edit 2: Nevermind, I found some issues. Here is a snippet of the error window: Error snippet

Binary::Binary(Binary& copyBinary, bool alias) { //I had to send a snippet because text formatting wasn't working
    if (alias) {
        triboolList = copyBinary.triboolList; //tribool List is defined as "tribool* triboolList;"
    }
    else {
        triboolList = new tribool[triLength(copyBinary.triboolList)];
        for (int i = 0; i < triLength(copyBinary.triboolList); i++) {
            triboolList[i] = (const tribool)copyBinary.triboolList[i];
        }
        triboolList[triLength(copyBinary.triboolList)] = DELIM;
    }
}

>Solution :

Replace the expression triLength(copyBinary.triboolList) by X:

triboolList = new tribool[X];
for (int i = 0; i < X; i++) {
    triboolList[i] = (const tribool)copyBinary.triboolList[i];
}
triboolList[X] = DELIM;

You can now plainly see the error: it is illegal to access an array of size X at index X, since the last valid index is X-1.