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C# Fixed Array

This article covers declaring a C++ style fixed-size structure was difficult in earlier versions of C#. But with advanced versions of C# fixed size array are possible. We are not discussing here about the array length or static or dynamic array which deals with an array capacity.

In .NET normally arrays are reference types and an array declared as part of a structure doesn’t physically exist inside the struct.

Only a reference to the array is placed inside the structure, which points to the original location of the array on the heap. Lets look in detail on C# fixed size array in struct.

Fixed Size Buffer In C#

In C# 2.0, it’s now possible to declare arrays in structure as fixed-sized inside unsafe code blocks. Fixed arrays will typically be part of a structure that’s passed to a native API.

public unsafe struct CharArray

Buffers with a set size. The fixed statement in C# allows you to create a data structure buffer with a fixed size array. All that’s required is for the array type to be of short, int, long, sbyte, ushort, uint,  ulong, float, double, char, bool or byte.

When writing methods that interact with data sources from other programming languages or platforms, fixed size buffers come in handy.

C# Fixed Size Buffer Sample

Lets see how we can define fixed size array in C# to have them in struct

public unsafe struct DataStructSample
{
     public int aNumber;
     public fixed float aArray[5];
}

Benefits Of Fixed Size Buffer In C#

As in C++, the size of the built-in arrays must be maintained. The same is true for fixed size buffers in C#. This data type is similar to inline array in functionality.

Fixed size buffers in C# will someway  benefits like static code checking. Because they aren’t a standard part of C#, they’re a pain to use. As a result, it’s probably best to keep struct’s size as part of it. Either that or use a collection such as Array in C#. Fixing the buffer and then making it part of other structures with other data could be an alternative solution.

C# Fixed Buffer Attribute sample

We can use the FixedBufferAttribute to create a fixed-size buffer in C#. This FixedBuffer attribute can be applied to fields of a class or a struct.

See an example showing how to use FixedBuffer attribute in C#

struct FixedSizeBuffer
{
    [FixedBuffer(typeof(int), 4)]
    public Buffer bufferStruct;

    public struct Buffer
    {
        public int i;
        public int j;
        public int k;
        public int l;
    }
}

Here above, struct Buffer is a fixed-size buffer of 4 integers.

You can access the elements of the struct using the field names as shown below

FixedSizeBuffer fixedSizeBuffer;

fixedSizeBuffer.bufferStruct.i = 2;
fixedSizeBuffer.bufferStruct.j = 3;
fixedSizeBuffer.bufferStruct.k = 4;
fixedSizeBuffer.bufferStruct.l = 5;

Console.WriteLine(fixedSizeBuffer.bufferStruct.i); 
console.WriteLine(fixedSizeBuffer.bufferStruct.j);
console.WriteLine(fixedSizeBuffer.bufferStruct.k); 
console.WriteLine(fixedSizeBuffer.bufferStruct.l); 

FixedBufferAttribute is only a feature available in the .NET Framework. Mono & .NET Core won’t have FixedBuffer attribute.

FAQ on C# Fixed Arrays

How to Declare Fixed-size array of struct type in C#?

In C# we can have fixed size buffer of the types
long, int, short, ushort, uint, ulong, bool, byte, char,sbyte, float or double.

Example,

unsafe struct FixedSizeArraySample 
{ 
   public int intNumber;
   public fixed Byte abyte[15];
   fixed float fixedArray[4]; 
}

Summary

This article covered C# Fixed Size Buffer. When writing methods that interact with data sources from other programming languages or platforms, fixed size buffers come in handy. Any attributes or modifiers allowed for regular struct members can be applied to the fixed array. Hope you found this article helpful. Share your thought on C# fixed arrays in the comment section below.

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