sizeof() equivalent for reference types?
I\'m looking for a way to get the size of an instance of a reference type. sizeof is only for value types. Is this possible?
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I had a similar question recently and wanted to know the size of Object and LinkedListNode in C#. To solve the problem, I developed a program that would:
- Measure the program's "Working Set"
- Allocate a lot of objects.
- Measure the "Working Set" again.
- Divide the difference by the number of allocated objects.
On my computer (64-bit), I got the following data:
Measuring Object: iter working set size estimate -1 11190272 1000000 85995520 74.805248 2000000 159186944 73.998336 3000000 231473152 73.4276266666667 4000000 306401280 73.802752 5000000 379092992 73.580544 6000000 451387392 73.3661866666667 7000000 524378112 73.3125485714286 8000000 600096768 73.613312 9000000 676405248 73.9127751111111 Average size: 73.7577032239859 Measuring LinkedListNodeBased on the data, the average size of allocating millions of Objects is approximately 29.2 bytes. A LinkedListNode object is approximately 44.5 bytes. This data illustrates two things:
- It's very unlikely that the system is allocating a partial byte. The fractional measure of bytes indicates the overhead the CLR requires to allocate and track millions of reference types.
- If we simply round-down the number of bytes, we're still unlikely to have the proper byte count for reference types. This is clear from the measure of Objects. If we round down, we assume the size is 29 bytes which, while theoretically possible, is unlikely because of padding. In order to improve performance, object allocations are usually padded for alignment purposes. I would guess that CLR objects will be 4 byte aligned.
Assuming CLR overhead and 4-byte alignment, I'd estimate an Object in C# is 28 bytes and a LinkedListNode is 44 bytes.
BTW Jon Skeet had the idea for the method above before I did and stated it in this answer to a similar question.
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