How to remove data from a MemoryStream

c# .net memorystream
LEM picture LEM · Apr 20, 2011 · Viewed 23.5k times · Source

I cannot get this to work. I have a MemoryStream object. This class has a Position property that tells you how many bytes you have read.

What I want to do is to delete all the bytes between 0 and Position-1

I tried this:

MemoryStream ms = ...
ms.SetLength(ms.Length - ms.Position);

but at some point my data gets corrupted.

So I ended up doing this

MemoryStream ms = ...
byte[] rest = new byte[ms.Length - ms.Position];
ms.Read(rest, 0, (int)(ms.Length - ms.Position));
ms.Dispose();
ms = new MemoryStream();
ms.Write(rest, 0, rest.Length);

which works but is not really efficient.

Any ideas how I can get this to work?

Thanks

Answer

eselk picture eselk · May 10, 2013

This should work and be much more efficient than creating a new buffer:

byte[] buf = ms.GetBuffer();            
Buffer.BlockCopy(buf, numberOfBytesToRemove, buf, 0, (int)ms.Length - numberOfBytesToRemove);
ms.SetLength(ms.Length - numberOfBytesToRemove);

MemoryStream.GetBuffer() gives you access to the existing buffer, so you can move bytes around without creating a new buffer.

Of course you'll need to be careful about out-of-bounds issues.

Related questions

How to get a MemoryStream from a Stream in .NET?

I have the following constructor method which opens a MemoryStream from a file path: MemoryStream _ms; public MyClass(string filePath) { byte[] docBytes = File.ReadAllBytes(filePath); _ms = new MemoryStream(); _ms.Write(docBytes, 0, docBytes.Length); } I need to change this to accept …

Read More
Is a memory leak created if a MemoryStream in .NET is not closed?

I have the following code: MemoryStream foo(){ MemoryStream ms = new MemoryStream(); // write stuff to ms return ms; } void bar(){ MemoryStream ms2 = foo(); // do stuff with ms2 return; } Is there any chance that the MemoryStream that I've allocated will somehow fail …

Read More
StreamWriter writing to MemoryStream

I was under the impression that when you called Flush() in a StreamWriter object it writes to the underlying stream, but apparently this isn't the case with my code. Instead of writing to my file it will just write nothing. …

Read More