我可以在.NET 4.5下创建的最大数组是什么？

Question

I'm experimenting with memory limits on my x64 machine (Windows7) under .NET 4.5. Based on this documentation (as referred to in this answer ) it seems like I should be able to create an array with up to UInt32.MaxValue elements. So I enabled gcAllowVeryLargeObjects and tried to create the following array:

int[] arr = new int[UInt32.MaxValue]; //2^32

However, this generates an OverflowException: ("Arithmetic operation resulted in an overflow.")

So I tried this instead,

int[] arr = new int[UInt32.MaxValue/2];   //2^31  (i.e., 2 * 1024 * 1024 * 1024)

and it throws a 'System.OutOfMemoryException'.

What am I missing here, and what in fact is the largest integer array that I can create?

---

UPDATE: So, as it turns out, the largest array I can create is:

int[] arr = new int[(long)(1.999 * 1024 * 1024 * 1024)]; //just shy of 2^31

So why can't I reach the limit that the documentation leads me to expect?

Answer 1

From your link:

The maximum index in any single dimension is 2,147,483,591 (0x7FFFFFC7) for byte arrays and arrays of single-byte structures, and 2,146,435,071 (0X7FEFFFFF) for other types.

You're exceeding that limit, still.

This should give a darn big array, though:

int[,] arr = new int[UInt32.MaxValue/3,3];
//                 comes out even ^^^

The total size of that array, which contains the maximum number of elements, should be (16 GB - 4 bytes + metadata) Use an even larger value type to really put the hurt on your PC.