C++ union in C#

struct Foo {
    float bar;

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

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

public struct Foo
{
    float bar;
    int Kilroy;
    float Fubar;
}

struct LibrarySType {
AnotherType *anotherTypeBuff;
int oneSetOfFlags;
int anotherSetOfFlags;
union {
  struct {
    int structMember1;
    ...
  } oneUseOfThisLibraryType;
  struct {
    char *structMember2;
    ...
  } anotherUseOfThisLibraryType;
  ...
} u;
int64 *moreStuff;
... you get the idea