您可以使用MemoryStream.WriteTo或Stream.CopyTo（框架版本4.5.2、4.5.1、4.5、4支持）方法将内存流的内容写入另一个流。

memoryStream.WriteTo(fileStream);

更新：

fileStream.CopyTo(memoryStream);
memoryStream.CopyTo(fileStream);

假设内存流名称为ms。
此代码将MemoryStream写入文件：

using (FileStream file = new FileStream("file.bin", FileMode.Create, System.IO.FileAccess.Write)) {
   byte[] bytes = new byte[ms.Length];
   ms.Read(bytes, 0, (int)ms.Length);
   file.Write(bytes, 0, bytes.Length);
   ms.Close();
}

这个函数将一个文件读入内存流：

using (MemoryStream ms = new MemoryStream())
using (FileStream file = new FileStream("file.bin", FileMode.Open, FileAccess.Read)) {
   byte[] bytes = new byte[file.Length];
   file.Read(bytes, 0, (int)file.Length);
   ms.Write(bytes, 0, (int)file.Length);
}

在.Net Framework 4+中，您可以简单地将FileStream复制到MemoryStream，然后进行反向操作，就像这样简单：

MemoryStream ms = new MemoryStream();
using (FileStream file = new FileStream("file.bin", FileMode.Open, FileAccess.Read))
    file.CopyTo(ms);

反之亦然（内存流到文件流）：

using (FileStream file = new FileStream("file.bin", FileMode.Create, System.IO.FileAccess.Write))
    ms.CopyTo(file);

即使出现异常（很可能是文件I/O），数据流也应该被处理掉--使用子句是我最喜欢的方法，所以在编写MemoryStream时，可以用途：

using (FileStream file = new FileStream("file.bin", FileMode.Create, FileAccess.Write)) {
    memoryStream.WriteTo(file);
}

为了让你重温：

using (FileStream file = new FileStream("file.bin", FileMode.Open, FileAccess.Read)) {
    byte[] bytes = new byte[file.Length];
    file.Read(bytes, 0, (int)file.Length);
    ms.Write(bytes, 0, (int)file.Length);
}

如果文件很大，那么值得注意的是，阅读操作将使用两倍于文件总大小的内存。一个解决方案是从字节数组创建MemoryStream-以下代码假设您不会写入该流。

MemoryStream ms = new MemoryStream(bytes, writable: false);

我的研究（下面）表明，内部缓冲区与您传递的字节数组相同，因此它应该可以保存内存。

byte[] testData = new byte[] { 104, 105, 121, 97 };
var ms = new MemoryStream(testData, 0, 4, false, true);
Assert.AreSame(testData, ms.GetBuffer());

对于任何寻找简短版本的人：

var memoryStream = new MemoryStream(File.ReadAllBytes("1.dat"));

File.WriteAllBytes("1.dat", memoryStream.ToArray());

写入文件的组合答案可以是;

MemoryStream ms = new MemoryStream();    
FileStream file = new FileStream("file.bin", FileMode.Create, FileAccess.Write);
ms.WriteTo(file);
file.Close();
ms.Close();

对于加载文件，我更喜欢这个

MemoryStream ms = new MemoryStream();
using (FileStream fs = File.OpenRead(file))
{
    fs.CopyTo(ms);
}

保存到文件中

Car car = new Car();
car.Name = "Some fancy car";
MemoryStream stream = Serializer.SerializeToStream(car);
System.IO.File.WriteAllBytes(fileName, stream.ToArray());

从文件加载

using (var stream = new MemoryStream(System.IO.File.ReadAllBytes(fileName)))
{
    Car car = (Car)Serializer.DeserializeFromStream(stream);
}

其中

using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

namespace Serialization
{
    public class Serializer
    {
        public static MemoryStream SerializeToStream(object o)
        {
            MemoryStream stream = new MemoryStream();
            IFormatter formatter = new BinaryFormatter();
            formatter.Serialize(stream, o);
            return stream;
        }

        public static object DeserializeFromStream(MemoryStream stream)
        {
            IFormatter formatter = new BinaryFormatter();
            stream.Seek(0, SeekOrigin.Begin);
            object o = formatter.Deserialize(stream);
            return o;
        }
    }
}

最初这个类的实现已经发布here
以及

[Serializable]
public class Car
{
    public string Name;
}

我使用面板控件来添加图像，甚至是流视频，但是你可以在SQL Server上将图像保存为Image，或者在MySQL上将图像保存为largeblob。这段代码对我来说很有用。看看吧。
在此保存图像

MemoryStream ms = new MemoryStream();
Bitmap bmp = new Bitmap(panel1.Width, panel1.Height);
panel1.DrawToBitmap(bmp, panel1.Bounds);
bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg); // here you can change the Image format
byte[] Pic_arr = new byte[ms.Length];
ms.Position = 0;
ms.Read(Pic_arr, 0, Pic_arr.Length);
ms.Close();

在这里你可以加载，但我用了一个PictureBox控件。

MemoryStream ms = new MemoryStream(picarr);
ms.Seek(0, SeekOrigin.Begin);
fotos.pictureBox1.Image = System.Drawing.Image.FromStream(ms);

希望能帮上忙。

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Text;

namespace ImageWriterUtil
{
    public class ImageWaterMarkBuilder
    {
        //private ImageWaterMarkBuilder()
        //{
        //}
        Stream imageStream;
        string watermarkText = "©8Bytes.Technology";
        Font font = new System.Drawing.Font("Brush Script MT", 30, FontStyle.Bold, GraphicsUnit.Pixel);
        Brush brush = new SolidBrush(Color.Black);
        Point position;
        public ImageWaterMarkBuilder AddStream(Stream imageStream)
        {
            this.imageStream = imageStream;
            return this;
        }
        public ImageWaterMarkBuilder AddWaterMark(string watermarkText)
        {
            this.watermarkText = watermarkText;
            return this;
        }
        public ImageWaterMarkBuilder AddFont(Font font)
        {
            this.font = font;
            return this;
        }

        public ImageWaterMarkBuilder AddFontColour(Color color)
        {
            this.brush = new SolidBrush(color);
            return this;
        }
        public ImageWaterMarkBuilder AddPosition(Point position)
        {
            this.position = position;
            return this;
        }

        public void CompileAndSave(string filePath)
        {

            //Read the File into a Bitmap.
            using (Bitmap bmp = new Bitmap(this.imageStream, false))
            {
                using (Graphics grp = Graphics.FromImage(bmp))
                {

                    //Determine the size of the Watermark text.
                    SizeF textSize = new SizeF();
                    textSize = grp.MeasureString(watermarkText, font);

                    //Position the text and draw it on the image.
                    if (position == null)
                        position = new Point((bmp.Width - ((int)textSize.Width + 10)), (bmp.Height - ((int)textSize.Height + 10)));
                    grp.DrawString(watermarkText, font, brush, position);

                    using (MemoryStream memoryStream = new MemoryStream())
                    {
                        //Save the Watermarked image to the MemoryStream.
                        bmp.Save(memoryStream, ImageFormat.Png);
                        memoryStream.Position = 0;
                       // string fileName = Path.GetFileNameWithoutExtension(filePath);
                        // outPuthFilePath = Path.Combine(Path.GetDirectoryName(filePath), fileName + "_outputh.png");
                        using (FileStream file = new FileStream(filePath, FileMode.Create, System.IO.FileAccess.Write))
                        {
                            byte[] bytes = new byte[memoryStream.Length];
                            memoryStream.Read(bytes, 0, (int)memoryStream.Length);
                            file.Write(bytes, 0, bytes.Length);
                            memoryStream.Close();
                        }
                    }
                }
            }

        }
    }
}

用法：-

ImageWaterMarkBuilder.AddStream(stream).AddWaterMark("").CompileAndSave(filePath);