c# MemoryStream vs Byte Array

57
votes

I have a function, which generates and returns a MemoryStream. After generation the size of the MemoryStream is fixed, I dont need to write to it anymore only output is required. Write to MailAttachment or write to database for example.

What is the best way to hand the object around? MemoryStream or Byte Array? If I use MemoryStream I have to reset the position after read.

3
c#asp.net.net
How often do you need to re-read the data? – Oded
It depends. Sometimes only once, sometimes 2-3 times. – LuckyStrike
If you pass a Byte array then are you creating a new MemoryStream everywhere you use it? – Dan Puzey
At the moment I use MemoryStream. I have a wrapper around MemoryStream and a method that convert MemoryStream to byte array. – LuckyStrike
How big are the results? That's the thing that matters most. – Henk Holterman

3 Answers

69
votes

If you have to hold all the data in memory, then in many ways the choice is arbitrary. If you have existing code that operates on Stream, then MemoryStream may be more convenient, but if you return a byte[] you can always just wrap that in a new MemoryStream(blob) anyway.

It might also depend on how big it is and how long you are holding it for; MemoryStream can be oversized, which has advantages and disadvantages. Forcing it to a byte[] may be useful if you are holding the data for a while, since it will trim off any excess; however, if you are only keeping it briefly, it may be counter-productive, since it will force you to duplicate most (at an absolute minimum: half) of the data while you create the new copy.

So; it depends a lot on context, usage and intent. In most scenarios, "whichever works, and is clear and simple" may suffice. If the data is particularly large or held for a prolonged period, you may want to deliberately tweak it a bit.

One additional advantage of the byte[] approach: if needed, multiple threads can access it safely at once (as long as they are reading) - this is not true of MemoryStream. However, that may be a false advantage: most code won't need to access the byte[] from multiple threads.

6
votes

The MemoryStream class is used to add elements to a stream. There is a file pointer; It simulates random access, it depends on how it is implemented. Therefore, a MemoryStream is not designed to access any item at any time.

The byte array allows random access of any element at any time until it is unassigned.

Next to the byte [], MemoryStream lives in memory (depending on the name of the class). Then the maximum allocation size is 4 GB.

Finally, use a byte [] if you need to access the data at any index number. Otherwise, MemoryStream is designed to work with something else that requires a stream as input while you just have a string.

1
votes

Use a byte[] because it's a fixed sized object making it easier for memory allocation and cleanup and holds relatively no overhead - especially since you don't need to use the functions of the MemoryStream. Further you want to get that stream disposed of ASAP so it can release the possible unmanaged resources it may be using.