Incorrect Array Copy (IAC)

Description:

IAC checks the semantics of the array copy library method (System.Array.Copy()). The audit detects for the possibility of incorrectly swapping argument positions. The order of copying array method arguments (source and destination) is unnatural (especially for C programmers who are familiar with the memcpy() function): unlike assignment operations, the source is specified before the destination. Usually, the copy array method is used to copy data from an existing array to a newly-created one. Generally, it does not make sense to copy data from an array that has just been created. This audit detects situations when the source argument refers to the array that was created just before the array copy.

Incorrect:

class Buffer {
    private int[] buf;
    private int   used;

    private void Extend(int size) { 
        if (used + size > buf.Length) {
            int newSize = used + size > used * 2 ? used + size : used * 2;
            int[] newBuf = new int[newSize];
            System.Array.Copy(newBuf, buf, used);
            buf = newBuf;
        }
        used += size;
    }
}

Correct:

class Buffer {
    private int[] buf;
    private int   used;

    private void Extend(int size) { 
        if (used + size > buf.Length) {
            int newSize = used + size > used * 2 ? used + size : used * 2; 
            int[] newBuf = new int[newSize];
            System.Array.Copy(buf, newBuf, used);
            buf = newBuf;
        }
        used += size;
    }
}