Viktor Elofsson Viktor Elofsson - 2 months ago 38
C++ Question

C++ union in C#

I'm translating a library written in C++ to C#, and the keyword 'union' exists once. In a struct.

What's the correct way of translating it into C#? And what does it do? It looks something like this;

struct Foo {
float bar;

union {
int killroy;
float fubar;
} as;
}

Answer

You can use explicit field layouts for that:

[StructLayout(LayoutKind.Explicit)] 
public struct SampleUnion
{
    [FieldOffset(0)] public float bar;
    [FieldOffset(4)] public int killroy;
    [FieldOffset(4)] public float fubar;
}

Untested. The idea is that two variables have the same position in your struct. You can of course only use one of them.

More informations about unions in struct tutorial