How do you write to a file using memory-mapped I/O?

Question

ICSM Computer · Answer

Writing to a file using memory-mapped I/O in C# is done with the
MemoryMappedFile class. This technique allows you to treat a file as if it's in memory, which can offer performance benefits for large files or for inter-process communication.
Basic Example: Write using Memory-Mapped File
using System;
using System.IO;
using System.IO.MemoryMappedFiles;
using System.Text;
class Program
{
    static void Main()
    {
        string path = "example.dat";
        string text = "Hello from memory-mapped file!";
        byte[] data = Encoding.UTF8.GetBytes(text);
        // Create or overwrite the file and ensure it's large enough
        using (var file = new FileStream(path, FileMode.Create, FileAccess.ReadWrite, FileShare.None))
        {
            file.SetLength(data.Length); // Set file size
        }
        // Open the file as a memory-mapped file
        using (var mmf = MemoryMappedFile.CreateFromFile(path, FileMode.Open))
        {
            using (var accessor = mmf.CreateViewAccessor(0, data.Length, MemoryMappedFileAccess.Write))
            {
                accessor.WriteArray(0, data, 0, data.Length);
            }
        }
        Console.WriteLine("Data written to file using memory-mapped I/O.");
    }
}
Breakdown:
MemoryMappedFile.CreateFromFile(...): Maps a file to memory.CreateViewAccessor(...): Gets a memory-accessible view of the file.accessor.WriteArray(...): Writes bytes directly into the mapped memory.
Notes:
Ideal for large files or random access patterns.Can also be used for inter-process communication (IPC).You must pre-size the file using SetLength() to avoid IOException.
Gotchas:
You need to manage memory ranges carefully — writing beyond allocated size causes exceptions.Not suitable for simple small file writes (overhead not worth it).
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How do you write to a file using memory-mapped I/O?

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Basic Example: Write using Memory-Mapped File

Breakdown:

Notes:

Gotchas:

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