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C#: sizeof

Handbook C# · Practical Guide

Returns the size of the unmanaged type in bytes. No unsafe context is required for certain primitives.

Simple example (Example.cs)

Save this example separately as Example.cs. Run it independently of the other examples on this page.

Example.cs:

// PROJECT-EXAMPLE
System.Console.WriteLine(sizeof(int));

Result:

4

Syntax

sizeof(Type)

In .csproj, set true. For managed data, it's usually easier to work through Span without raw pointers.

Example 1: simple form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        unsafe { int* values = stackalloc int[2]; values[0] = 3; values[1] = 7; Console.WriteLine(values[0] + values[1]); Console.WriteLine(sizeof(int)); }
    }
}

Example 2: another practical form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        int[] values = [2, 4, 6];
        unsafe { fixed (int* pointer = values) { pointer[1] = 9; Console.WriteLine(*(pointer + 1)); Console.WriteLine(sizeof(long)); } }
        Console.WriteLine(values[1]);
    }
}

Official source: Microsoft Learn.