using System.IO.MemoryMappedFiles;

var mmf = MemoryMappedFile.CreateFromFile(
    filePath, FileMode.OpenOrCreate, null, fileSize);

long fileSize = 1024 *  // = 1 KB
                1024 *  // = 1 MB
                100;    // = 100 MB

using var accessor = mmf.CreateViewAccessor();
string dataToWrite = "Hello, Memory-Mapped Files!";
byte[] dataBytes = Encoding.UTF8.GetBytes(dataToWrite);
accessor.WriteArray(30, dataBytes, 0, dataBytes.Length);

byte[] readData = new byte[2];
accessor.ReadArray(34, readData, 0, 2);
string readDataString = Encoding.UTF8.GetString(readData);