Datatypes for MemoryStream.Capacity vs MemoryStream.Length

Question

Today I noticed something strange with the MemoryStream class. The .Length property is a long, but the .Capacity property, which should presumably always be >= .Length is only an int.

I know that it would take a stream of over a GB to for Length to exceed possible Capacity, but this seems very strange to me. Length can't be changed, because it's inherited from Stream, but why not make Capacity a long as well? What happens to the capacity if you do have a MemoryStream that exceeds int.MaxValue in length?

Answer 1

No, MemoryStream.Capacity can't exceed the int.MaxValue because memory stream is backed by a byte[] and arrays maximum length is int.MaxValue.

However, Stream.Length is long, that makes sense because stream can be anything, For example FileStream.Length can be greater than int.MaxValue undoubtedly.

Answer 2

A fundamental limitation in .NET, unfortunately, is that objects cannot exceed 2GB in size. The Stream class needs the long for its Length property, because a Stream can represent a resource outside of .NET (e.g. a file), but since MemoryStream is known to always be an in-memory, managed object, it is guaranteed to always be able to fit its Capacity in an int.

Answer 3

The Length property is inherited from Stream, while the Capacity property is declared for MemoryStream. Streams in general may be larger than 2GB, but this particular kind of stream never will be -- hence, the Capacity that is specific to MemoryStream is just an int.