Internal working of List in c# [duplicate]

Question

Can anyone explain how List<T> works internally in C#?

 public List<ConvData> pdetails = new List<ConvData>();

How is it stored? What exactly happens when we call pdetails.Add();

Answer 1

List is implemented the same way C++'s vector, meaning the implementation allocate an array of a predefined size, fills that array, and when you want to add an element and the array is full the implementation allocate a new array, bigger, copies all values to the new array, and then adds the new value. This results with an AVERAGE performance of O(1) when adding, but not always.

Answer 2

Just take a look at the reference source from Microsoft and see how it works in detail.

Right now, the Add method looks like this:

// Adds the given object to the end of this list. The size of the list is
// increased by one. If required, the capacity of the list is doubled
// before adding the new element.
//
public void Add(T item) {
    if (_size == _items.Length) EnsureCapacity(_size + 1);
    _items[_size++] = item;
    _version++;
}