When should I use a struct rather than a class in C#?

Question

When should you use struct and not class in C#? My conceptual model is that structs are used in times when the item is merely a collection of value types. A way to

Answer 1

I use structs for packing or unpacking any sort of binary communication format. That includes reading or writing to disk, DirectX vertex lists, network protocols, or dealing with encrypted/compressed data.

The three guidelines you list haven't been useful for me in this context. When I need to write out four hundred bytes of stuff in a Particular Order, I'm gonna define a four-hundred-byte struct, and I'm gonna fill it with whatever unrelated values it's supposed to have, and I'm going to set it up whatever way makes the most sense at the time. (Okay, four hundred bytes would be pretty strange-- but back when I was writing Excel files for a living, I was dealing with structs of up to about forty bytes all over, because that's how big some of the BIFF records ARE.)