如何使用内存映射文件c#读写文件

Question

我在D驱动器中有一个图像，如"D: image 1.tiff"。我想读取此文件并将其写入另一个位置，例如在路径"D:Project"中。如何使用内存映射文件做到这一点?

Answer 1

我现在可以使用下面的编码实现使用内存映射文件读取和写入文件:

FileStream stream = File.OpenRead(@"D:FFv1dpx11.dpx");
byte[] fileBytes = new byte[stream.Length];
string Output = @"D:Vanthiya ThevanFFv1dpx12.dpx";
using (var fileStream = new FileStream(Output, FileMode.Create, FileAccess.ReadWrite, FileShare.ReadWrite))
using (MemoryMappedFile memoryMapped = MemoryMappedFile.CreateFromFile(fileStream, "MapName", fileBytes.Length,
MemoryMappedFileAccess.ReadWrite, new MemoryMappedFileSecurity(), HandleInheritability.Inheritable, true))
{
    var viewStream = memoryMapped.CreateViewStream();
    viewStream.Write(fileBytes, 0, fileBytes.Length); 
}

Answer 2

CreateFromFile方法从磁盘上的现有文件创建内存映射文件。下面的示例创建一个超大文件的一部分的内存映射视图，并操作其中的一部分。

using System;
using System.IO;
using System.IO.MemoryMappedFiles;
using System.Runtime.InteropServices;
class Program
{
    static void Main(string[] args)
    {
        long offset = 0x10000000; // 256 megabytes 
        long length = 0x20000000; // 512 megabytes 
        // Create the memory-mapped file. 
        using (var mmf = MemoryMappedFile.CreateFromFile(@"c:ExtremelyLargeImage.data", FileMode.Open,"ImgA"))
        {
            // Create a random access view, from the 256th megabyte (the offset) 
            // to the 768th megabyte (the offset plus length). 
            using (var accessor = mmf.CreateViewAccessor(offset, length))
            {
                int colorSize = Marshal.SizeOf<MyColor>();
                MyColor color;
                // Make changes to the view. 
                for (long i = 0; i < length; i += colorSize)
                {
                    accessor.Read(i, out color);
                    color.Brighten(10);
                    accessor.Write(i, ref color);
                }
            }
        }
    }
}
public struct MyColor
{
    public short Red;
    public short Green;
    public short Blue;
    public short Alpha;
    // Make the view brighter. 
    public void Brighten(short value)
    {
        Red = (short)Math.Min(short.MaxValue, (int)Red + value);
        Green = (short)Math.Min(short.MaxValue, (int)Green + value);
        Blue = (short)Math.Min(short.MaxValue, (int)Blue + value);
        Alpha = (short)Math.Min(short.MaxValue, (int)Alpha + value);
    }
}

下面的示例为另一个进程打开相同的内存映射文件。

using System;
using System.IO.MemoryMappedFiles;
using System.Runtime.InteropServices;

class Program
{
    static void Main(string[] args)
    {
        // Assumes another process has created the memory-mapped file. 
        using (var mmf = MemoryMappedFile.OpenExisting("ImgA"))
        {
            using (var accessor = mmf.CreateViewAccessor(4000000, 2000000))
            {
                int colorSize = Marshal.SizeOf<MyColor>();
                MyColor color;
                // Make changes to the view. 
                for (long i = 0; i < 1500000; i += colorSize)
                {
                    accessor.Read(i, out color);
                    color.Brighten(20);
                    accessor.Write(i, ref color);
                }
            }
        }
    }
}
public struct MyColor
{
    public short Red;
    public short Green;
    public short Blue;
    public short Alpha;
    // Make the view brigher. 
    public void Brighten(short value)
    {
        Red = (short)Math.Min(short.MaxValue, (int)Red + value);
        Green = (short)Math.Min(short.MaxValue, (int)Green + value);
        Blue = (short)Math.Min(short.MaxValue, (int)Blue + value);
        Alpha = (short)Math.Min(short.MaxValue, (int)Alpha + value);
    }
}

您也可以在:http://www.codeproject.com/Articles/138290/Programming-Memory-Mapped-Files-with-the-NET-Frame