Structs

Syntax

struct StructName {\n  // fields, properties, methods\n}

Examples

public struct Point
{
    public int X, Y;

    public Point(int x, int y)
    {
        X = x;
        Y = y;
    }

    public override string ToString() => $"({X}, {Y})";
}

Point p = new Point(3, 4);
Console.WriteLine(p);  // (3, 4)

public struct Point
{
    public int X, Y;
    public Point(int x, int y) { X = x; Y = y; }
}

Point original = new Point(1, 1);
Point copy = original;  // this COPIES the entire struct

copy.X = 99;

Console.WriteLine(original.X);  // 1 - unaffected by the change to copy
Console.WriteLine(copy.X);       // 99

// Compare to a class, where "copy" would just be another reference
// to the SAME object, and changing copy.X would also change original.X

public record struct Point(int X, int Y);

Point p1 = new Point(3, 4);
Point p2 = new Point(3, 4);

Console.WriteLine(p1 == p2);  // true - value equality, like a record
Console.WriteLine(p1);         // Point { X = 3, Y = 4 }

Best practices

• Use structs for small, immutable data groupings (roughly 16 bytes or less is a common guideline) where value-copy semantics make sense, like coordinates or RGB colors
• Use classes instead of structs for anything larger or that represents an entity with identity (a Customer, an Order) rather than a simple value
• Be aware that passing a large struct around by value can hurt performance due to repeated copying - pass by "in" or "ref" if a large struct must avoid copies
• Consider record struct (C# 10+) when you want both value equality and value-type copy semantics together

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation