`ArraySegment`

Often we need to track ranges in C# arrays. For example, part of an array might be used for a different purpose than other parts.

ArraySegment is a generic struct that stores information about an array range. We can create ArraySegments and pass them to methods to operate on parts of arrays.

An example

ArraySegment must have a type parameter—this must match the array type. Once you construct the ArraySegment, you can read the Array, Offset, and Count to retrieve its fields.

Info We use the original array, the Offset and Count properties, and loop through the elements specified in the ArraySegment.

Argument 1 The first argument to ArraySegment is the array—this must have the same type of elements as the ArraySegment.

Argument 2 This is the offset into the array—to start at the second element, pass the index 1.

Argument 3 This is the count of elements (not the end index) that is being referred to by the ArraySegment.

using System;

// Create an ArraySegment from this array.
int[] array = { 10, 20, 30 };
ArraySegment<int> segment = new ArraySegment<int>(array, 1, 2);

// Write the array.
Console.WriteLine("-- Array --");
int[] original = segment.Array;
foreach (int value in original)
{
    Console.WriteLine(value);
}

// Write the offset.
Console.WriteLine("-- Offset --");
Console.WriteLine(segment.Offset);

// Write the count.
Console.WriteLine("-- Count --");
Console.WriteLine(segment.Count);

// Write the elements in the range specified in the ArraySegment.
Console.WriteLine("-- Range --");
for (int i = segment.Offset; i <= segment.Count; i++)
{
    Console.WriteLine(segment.Array[i]);
}-- Array --
10
20
30
-- Offset --
1
-- Count --
2
-- Range --
20
30

Discussion

Let's say you have a large data array, and want to call methods that act upon different parts of this large array. Copying these parts would cause increased memory usage.

So Pass an ArraySegment to these methods as an argument. In these methods, use the ArraySegment to access the large array.

A summary

ArraySegment allows you to specify a range inside a specific array. You can access properties of the ArraySegment to access the original data and also the positional data.