Append two or more byte arrays in C#

Question

Is there a best (see below) way to append two byte arrays in C#?

Pretending I have complete control, I can make the first byte array sufficiently large to hold the second byte array at the end and use the Array.CopyTo function. Or I can loop over individual bytes and make an assignment.

Are there better ways? I can't imagine doing something like converting the byte arrays to string and joining them and converting them back would be better than either method above.

In terms of best/better (in order):

1. Fastest
2. Least RAM consumption

A constraint is that I must work in the .NET 2.0 framework.

The two choices recommended are MemoryStream and BlockCopy. I have run a simple speed test of 10,000,000 loops 3 times and got the following results:

Average of 3 runs of 10,000,000 loops in milliseconds:

• BlockCopy Time: 1154, with a range of 13 milliseconds
• MemoryStream GetBuffer Time: 1470, with a range of 14 milliseconds
• MemoryStream ToArray Time: 1895, with a range of 3 milliseconds
• CopyTo Time: 2079, with a range of 19 milliseconds
• Byte-by-byte Time: 2203, with a range of 10 milliseconds

Results of List<byte> AddRange over 10 million loops: List<byte> Time: 16694

Relative RAM Consumption (1 is baseline, higher is worse):

• Byte-by-byte: 1
• BlockCopy: 1
• Copy To: 1
• MemoryStream GetBuffer: 2.3
• MemoryStream ToArray: 3.3
• List<byte>: 4.2

The test shows that in general, unless you are doing a lot of byte copies [which I am], looking at byte copies is not worth a focus [e.g. 10 million runs yielding a difference of as much as 1.1 seconds].

Answer 1

You want BlockCopy

According to this blog post it is faster than Array.CopyTo.

Answer 2

You could also use an approach with a MemoryStream. Suppose b1 and b2 are two byte arrays, you can get a new one, b3, by using the MemoryStream in the following fashion:

var s = new MemoryStream(); s.Write(b1, 0, b1.Length); s.Write(b2, 0, b2.Length); var b3 = s.ToArray(); 

This should work without LINQ and is in fact quite a bit faster.