MappedFileTest.cs

// Tested with .NET Core 2.2, will likely work with the rest of the runtimes
using System;
using System.Diagnostics;
using System.IO.MemoryMappedFiles;
using System.Linq;
using System.Runtime.InteropServices;

namespace MappedFileTest
{
	static class Program
	{
		const int fileLength = 1024;

		static IntPtr getRawPointer( this MemoryMappedViewAccessor acc )
		{
			return acc.SafeMemoryMappedViewHandle.DangerousGetHandle();
		}

		static MemoryMappedFile createTest( string name, int length )
		{
			long size = length * 4;
			MemoryMappedFile mmf = MemoryMappedFile.CreateNew( name, size );
			int[] data = Enumerable.Range( 0, length ).ToArray();
			using( var mma = mmf.CreateViewAccessor( 0, size ) )
				mma.WriteArray( 0, data, 0, length );
			return mmf;
		}

		static void Main( string[] args )
		{
			// Create a memory mapped file with a unique name
			string name = Guid.NewGuid().ToString( "D" ).ToLowerInvariant();
			using( var file = createTest( name, fileLength ) )
			{
				// Open that file by name
				using( var openned = MemoryMappedFile.OpenExisting( name, MemoryMappedFileRights.Read ) )
				using( var acc = openned.CreateViewAccessor( 0, fileLength * 4, MemoryMappedFileAccess.Read ) )
				{
					// Get raw pointer
					IntPtr rawPointer = acc.getRawPointer();
					// Read a single int from unmanaged memory at that pointer
					int i42 = Marshal.ReadInt32( rawPointer + 42 * 4 );
					Debug.Assert( 42 == i42 );
					Console.WriteLine( "{0}", i42 );
				}
			}
		}
	}
}