Arrays, memory

Arrays are memory-efficient. Lists are built on top of arrays. Because of this, Lists use more memory to store the same data.

We provide a detailed comparison of array and List memory usage. A simple benchmark can be used to measure the memory of lists and arrays.

We focus on how the 2 data structures perform. The 2 code examples contrast how you can use an array with more complex logic, and a List with simpler logic.

Here The List collection is built up at runtime. It may have to allocate or change the positions in memory during garbage collection.

Note The int array is declared and created in one statement. Thus it will store all values in neighboring memory.

using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Compare time to build up a List.
        List<int> list = new List<int>();
        for (int i = 0; i < 60000; i++)
        {
            list.Add(i);
        }
    }
}using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Compare time to allocate an array and assign to it.
        int[] array = new int[60000];
        for (int i = 0; i < 60000; i++)
        {
            array[i] = i;
        }
    }
}List generic:  6.172 MB
Integer array: 5.554 MBList generic:  1043.4 ms
Integer array:  980.2 ms

Discussion

Arrays and Lists can change performance and memory usage. The benchmarks were taken from a more complex program, but they show the pattern of arrays being more efficient.

And Arrays were about 7% faster, even when other code is involved. The usage was with a data structure that looks up items.

Further For memory usage, the int array was more compact than the List generic. Arrays can lead to memory reductions over generics.

Notes, generics

You might be able to convert from generics to arrays. You could store the size of the array and use it when initializing later. That way you don't have to resize anything.

Tip These findings are only useful as a hint of how you can influence performance by changing from a List to an array.

Summary

We saw a comparison of List and array memory usage in the C# language. For speed it is sometimes worthwhile to prefer regular arrays. The performance benefit is significant.